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Discussion Starter #1
Ok, I have been reading magazines, several forums and various how-tos for months now on the proper way to tune carbs.

I am confused on a particular symptom and how it relates to the mixture being rich or lean, however, because I have seen this symptom described as both.

I am at approx. 2500 ft. and I have Sarachu slip-ons installed.

Say I am cruising along at 4,000RPM and I go WOT (that's wide open throttle, we use it on car boards, haven't really seen it used on motorcycle boards, hence the explanation). The engine will do what I call bogging - it will basically just stop, the exhaust sound stops, for just a quick second or so, and then it will start accelerating up the RPM range.

Now same situation but instead of WOT I open the throttle slowly and smoothly. The bike just accelerates smoothly.

And now my confusion - depending on where I have been reading, I have seen descriptions that such a thing means that when I go WOT the carbs are getting filled faster than the the airstream can handle and they basically drown for a second (IE too much fuel, rich). Or that when I go WOT the air comes faster than the fuel can keep up with and they starve for a second (IE too little fuel, lean).

Now I know for SURE that it can't be both situations. It's a little trying to go ride around for a while, stop, mess with the pilot screws, get back on and go ride some more, basically not having a clue if I'm even tuning in the right direction.

Can someone please set me straight on what this means? Thanks!!

EDIT
Let me add also that I started tuning at 2.5 turns out, I am at 3.25 turns out, the bogging is still present, which makes me think it's too rich, but the symptoms still go away as the engine warms up, which I have heard is a lean issue. And this happened right away with the change to the Sarachus so I know it's related to them and not something else happening, unless there was an extraordinary cosmic coincidence. ARGH!!
 

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EDIT
"Let me add also that I started tuning at 2.5 turns out, I am at 3.25 turns out, the bogging is still present, which makes me think it's too rich, but the symptoms still go away as the engine warms up, which I have heard is a lean issue. And this happened right away with the change to the Sarachus so I know it's related to them and not something else happening, unless there was an extraordinary cosmic coincidence. ARGH!!"

If I'm reading the above correctly you don't have a problem. You must always tune with a fully warmed engine. To do otherwise is foolish. The fuel cannot vaporize completely in a cold intake passage and you'll get lean Symptoms. Your description in your first paragraph sound like a rich condition. But all bets are off until the engine is fully warm.

FOG
 

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Discussion Starter #3
Ok so let me ask this then - do I just have to accept that the engine will not run very well until it is fully warmed up? I'm not whining, just curious. :)
 

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Discussion Starter #4
Lucky#13 said:
Well you can put it on a DYNO or take off those loud aftermarket pipes and go back to stock . And if you want it to get worse throw on a K&N filter and let the real fun begin. ;D
Also DYNO-JET has a 1-800# and will be more than happy to help if you tell the it has one of their kits in it. ;)
Har har. I have not jetted, nor do I intend to jet, the bike. I also don't intend to swap the intake. And due to my altitude and desire to trade up to a ZX-6R later this year I haven't done the FOG's Dyno Proven Airbox mod. I don't care how much power my EX is making. I was just looking for a change in scenery with the pipes. Honestly I am this *holds thumb and index finger really close together* close to swapping back to the stockers and offering my Sarachus up for sale. They haven't even got 100mi on them. Because the bike with the stockers ran fine when super cold for whatever reason (or it ran as well as could be perceived with the stock exhaust).

I guess it just comes down to my lack of experience with carburetors as this is the first (and very likely last) carbed anything I've ever owned. I plug my car into a computer to tune it - quite a big difference.
 
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About the whole "warming up" thing, my bike never really exceeds ~1/8 of the way up the temp gauge. So is my bike never really warming up, or is that temperature at which I should think about tuning?
 

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Discussion Starter #6
smithmax said:
About the whole "warming up" thing, my bike never really exceeds ~1/8 of the way up the temp gauge. So is my bike never really warming up, or is that temperature at which I should think about tuning?
My bike when fully warmed up sits very close to the middle of the temp gauge. In the summer this happens really quickly but in the winter it seems to take a lifetime.

Does your fan never come on then?
 

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Dumping it wide open out of the power band will tend to go lean. It's part of the reason automobile carburetors have accellerator pumps that add a squirt of fuel on rapid throttle opening at low RPM.

The venturi isn't at its max efficiency when throttled back due to the lower than ideal volume going through it, an inherent function/flaw of a device required to function over a BROAD range. The manifold volume further dampens the pulse that will draw the fuel (or more accurately allow the atmospheric pressure to push) the fuel into the air stream. On a bike with a short runner intake, you can get away without accellerator pumps because the volume dampening the pulse is not so dramatic as an automobile with a big common manifold. The effect on a short individual intake runner isn't entirely eliminated but is tolerable because a smooth roll on, still fairly quick, will not cause the bog.

NOW, if it's STILL intolerable after doing all of the suggestions made here, a shimming of the needles to raise them could help, BUT...... almost ALL experience with these particular bikes suggests that's not necessary. It does help on some bikes, just not these, based on experience. If you're sure that all else is covered, float height, clean jets, etc. AND you're not being ultra finicky about dumping it open violently and expecting a good response, then you could shim the needles up, no more than .020", and see if that fixes it. I only suggest the option because it's easy to do and is just as easily reversed if it doesn't work. Again, experience says that all else being good, it's not necessary on these.

Quick check. Have you had the carbs off? If so, is it possible you've got an intake leak? It's easy to get the carbs in without the manifold rubbers well seated and age can also deteriorate the rubber effecting a leak.
 

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This info is courtesy of Factory Pro Tuning guide
"2. Midrange (full throttle /5k-7k)
Step 1 (Best Main Jet) must be selected before starting step 2!
Select best needle clip position
To get the best power at full throttle / 5k-7k rpm, adjust the needle height, after you have already selected the best main jet.
If the engine pulls better or is smoother at full throttle/5k-7k in a full throttle roll-on starting at <3k when cool but soft and/or rough when at full operating temperature, it is too rich in the midrange and the needle should be lowered. If the engine pulls better when fully warmed up but still not great between 5k-7k, try raising the needle to richen 5k-7k.
If the engine pulls equally well between 5k-7k when cooler as compared to fully warmed up, the needle height is probably properly set.
Do not pay too much attention to the low-end richness when you are changing needle clip positions - you still need to be using the clip position that produces the best full throttle / 5k-7k power in conjunction with the main jets (Step 1) that produce the best power at high rpm. You will deal with the low-end / cruise next.

You are lean which just make sense you add pipes that flow very slightly better than stock so you should need slightly more fuel than stock get some small washers around .020 thick and raise your needles about .020 at a time until the problems goes away probably 2 washers under each needle
 

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Wow... great thread.
 

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I can't let this one go just yet, The flow has nothing to do with the problem. Anthing that flows out , got in through the carbs, and therefore should have the same mixture as the (fictitious ) larger flow. The problem is the backpressure that's missing now has effectively changed the cam timing. This is the name of the game , and where the claimed gains in HP come from. Noe the jetting (re-jetting) to smother the flat spot (created by moving the power up the rev range) they just pour more fuel on that point until is fires well enough. But this is not "More" power. just replacing what was already there. Internal combustion engines are capable of running on a wide mixture range with 16 to 1 being Ideal. they will tolerate a little leaner to about 20 to 1. before miss fire, but happily run with ratios as rich as 9 to 1. Jet kits exploit this fact, and simply pour fuel on a missfire till it runs.

However My biggest complaint of Jet kits is the quality of them. I have seen several engines returned to me that had needles worn out and c clips that cut right through the stems of the needles Jet themselves that were marked the same but were diffrent size.
I'll say this thought there is one thing of value in there ... it's the paper with the tuning instruction. Go look in your buddies shi. can and fish out that paper (he threw it away with out reading it) and save you self the 80 bucks.

I'll throw this out, The engine I built and tuned Made a consistant 54 HP on a Dyno Jet. Dyno. Box stock with standard carb&jets and exhaust. The best pipeandajetkit bike I've seen made 55. 400 bucks for one lousy hp don't seem like much of a bargin.
And finally, Anecdotal stories of wheelies and such can be disregarded as fallacy.

FOG
 

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Air flow is exactly what we are talking about all an internal combustion is is an air pump why do people port heads, install high lift long durations cam, high performance exhaust, bigger valves on and on, it's all about getting more air through the engine, if you read what was written in the original post and the Factory Pro info I posted the bike is lean period. Back pressure correct there is less back pressure, well genius have you ever heard of Bernoulli's therm as pressure decreases velocity increase, and thats exactly whats happening here he installed a less restrictive exhaust there by decreasing pressure more air is coming through the carbs because the pressure is lower on the back side so you need more fuel, it has nothing to do with cam timing, it's simple physics if you want to argue it argue it with Bernoulli, If you don't think factory pro or dynojet know what they are talking about call them and tell them because I could care less about your problem with jet kits or jetting. Dude you been leading these people in the wrong direction for a long time, and frankly I'm tired of listening to your BS, let me sell yourself to you, you don't know crap from Crisco. You guys just keep following this clown, and some day when you move to bigger bike and go to that forum you'll see just how little the FOG had to offer, I'll scan and post my dyno sheet when I'm done, but I think a side from that I'm about done here. Good Luck to all, if I can help anyone with anything I'll be happy to just shoot me an email, I've got a couple good ideas off here for that I thank you. Hopefully I've help someone or given an idea to someone on here because that's what's important. FOG this forum is all yours, keep up those winning ways. You are the god of the EX500 world!!
 

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Can the verbal competition & down-talking be canned? It serves only to divide.
Experiences & priorities differ, & I have a lot to learn, & so selfishly benefit from all you guys.

The "air-pump" model of the internal combustion engine has a long history. And the combustion-chemistry portion that's smack-dab between the gasses IN and gasses OUT is huge.

Part of the trick with this engine, near as I can tell from what I've read on-line, is that the engine's STOCK in/out ports are maximized for a wide torque curve, not maximum hp, yes?

Being a twin there's only so much that can be done using a header for scavenging (helping the next exhaust pulse out, at some rpms anyway). Porting, polishing may help some at the top... but...

Consider the new Ninja 650- Fuel injected, ultra-modern parallel twin: 150 ccs bigger than our 500 (30%) but rated only 20-25% more hp. (Wish I knew more about the torque curves.) Certainly the 650 is running cleaner (pollutant-wise) and doesn't require a thumb choke... but if it's the latest & greatest design, and bigger... why isn't it at least proportionately more powerful?

A couple of articles on the Ninja 650 suggested that there is more potential for power, but at what price to a wide/flat torque curve? Apparently that'll get determined this racing season?

My bias is towards the flexibility of widely available torque, but my skills are medeocre at best & like the safety margin of that kind of engine.

But if the 500 can be set-up to crank higher rpms, taking advantage of PNP with properly set-up carbs, it seems that it should be able to crank out more total power. I don't know if the expense of the piston/rods/crank/cams/would be worth the power pay-back...

Has such been done?
 

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"Has such been done?".

Yep done , re done, and done again. everything form the easy stuff to $5000. billet cranks. New cylinders and pistons . you name it it's been done. You know what. None of it worked, Not for very long at least. The EX puts out 50 HP From 500 cc. that a 100 hp per liter. until about 10 years ago that was Formula 1 class stuff.
This engine is at it's very structural limits. That it is simply cannot contain any more power, without bursting.
The cam drive (chain) in the middle splits the engine in two and causes the crank to be two bearings too long. then they hang that monster flywheel out on one end. this causes whipping that'll snap it if rev ed much over the 10.5K on the dial. the rods are so weak they will open and spin bearings is rev ed.
The route to power is not through external junk like pipes and carbs. (These thing are only to facilitate the best action of the internal mods.) but from seriously altering the engines internals to raise the BMEP. That's Brake effective mean pressure. Do that and you'll blow through the gas seal at the head gasket.

Even the cases aren't strong enough to hold the transmission in. I thew away 6 set of cases in 10 years of racing because the main transmission bearings had pull the cases out of shape so bad oil would leak around the bearings and the seals wouldn't stay in.

As I have said many times, this is a fairly balanced combination of parts that make a decent beginners bike. Any at temps to make it do otherwise will ( as the sheriff in Blazing Saddles said about Mungo ) only make it mad.
 

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Discussion Starter #15
Well I have some bad news (sorta) and some good news (sorta).

I tried tuning some more and still could not eliminate the huge flat spot. It bugs me to no end as its right in the middle of a range I find myself in constantly as I have a lot of stop and going in my town on my way to work which is my primary use for my bike.

Anyway I decided today while I was at work that this evening I would put the carbs back to 2.5 turns, throw the stock pipes back on, and see what would happen. So I did.

And it worked just as I remembered. Tons of power, no flat spot, just as I remembered. And so...

...my Sarachus are going up for sale. I'll post in the For Sale section later on (they are going to go up on EBay so I will put the auction number in).

Plenty of people have made these things work, and maybe I'm expecting too much, and maybe my lack of experience with carbs it the problem, I don't really know, but I know that someone else will be happier with my Sarachus than I am.
 

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Art1989 said:
.... Back pressure correct there is less back pressure, well genius have you ever heard of Bernoulli's therm as pressure decreases velocity increase, and thats exactly whats happening here he installed a less restrictive exhaust there by decreasing pressure more air is coming through the carbs because the pressure is lower on the back side so you need more fuel, it has nothing to do with cam timing, it's simple physics if you want to argue it argue it with Bernoulli....
And you have just run loose and free with Bernoulli's law and abused it by using it as the beginning and end of the discussion and in so doing, have made some simplistic and wrong statements. I could accurately make some pretty disparaging remarks about your post in its abuse and simplistic approach to the actual science. You say that, "... he installed a less restrictive exhaust there by decreasing pressure more air is coming through the carbs because the pressure is lower on the back side so you need more fuel...". Do you mean he needs more fuel?... Or he needs more air/fuel mixture? If you are saying more fuel, you're wrong. If he needs more air fuel mixture, you're theoretically right and it's just the simple fact in theory , that he ACTUALLY decreased back pressure sufficient to realize the advantage of greater efficiency in the spent fuel exchange. Right there, I'm not sure that your case holds any water in this instance. The theory's right, just not proven that in this case you actually DID reduce back pressure. Does the stock muffler flow the volume the engine produces at any greater restriction than aftermarket? That's NOT been proven and performance changes will prove it's only marginally better if at all, and that's at ABSOLUTE best!

NOW, with that bit of simplicity brought into question, let's get to the REAL problem.... how a carburetor works. Yup, how a carburetor works. Analyze that, and show me how ANY THEORY you can find changes the fact that it mixes fuel in direct relation to the volume of air coming through it, REGARDLESS of how that air flow was originated. Reduced back pressure on an engine, or connected to the vacuum cleaner of your choice, it will deliver fuel in direct relation to the volume of air flowing through it, NOT how it happens to BE that air is drawn through it. SOOO, how does Bernoulli's law or ANY logic justify THAT little tidbit of simplicity. (Time saving hint: It doesn't.)

Soooo, why does an engine, any engine, sometimes encounter problems that jet changes DO help? Experience DOES say that's true..... sometimes. And THAT'S where the discussion could be, not attacking an individual while abusing a few scientific principles.

And last but not least, why did FOG use the analogy that it's like changing cam timing.... not that it DOES change it.... but it's LIKE it changes it. Your own in depth knowledge should be able to see the logic behind that statement when described as LIKE changing it and the demonstrative value of that as an instructing tool to someone still grasping for the idea of the whole picture. It's true. A more detailed explanation might help but that's FOG. ;) If it's not clear, ask and he'll probably embellish. I happen to understand his point and it's true. Once again, he's right... not smoooooth, but right nonetheless.

And finally, could FOG be more diplomatic in his manner? Sure, oftentimes. And he has had occasion to spoof himself over just that. Could he better explain himself? I'm sure, at times. Is his info wrong? I'm yet to find it. Do I agree with EVERYTHING he ever posted in its ENTIRETY? No, not exactly. But it's almost always a difference of degree, perceptions of acceptablilty of something, not fundamental rights and wrongs. His practical experience with these things is apparent, underscored with my OWN growing experience with them, and ANYTHING he has posted or has to say as it applies SPECIFICALLY to one of these, I'm going to listen to. And it WILL have merit. It WON'T be fundamentally wrong. If you can get past his sometimes abrasive style, he CAN help you out with an EX.

And FINALLY!... what ONE statement has FOG often repeated in regard to jet kits? That the only thing of value in it, as it applies to EX's, is THE INSTRUCTION SHEET! The information is useful. That's possibly a little abrasive by style BUT... experience says that the EX is already jetted near optimum WITHOUT the changes of hardware and that what it can benefit from is the turning of the pilot screws. The instruction sheet will help with the explanations of function and for the rare occasion that something more might help, it could be a good guide to that end, help with identifying that.

It's unfortunate that this happened. I've always professed that my love for machinery is based in the fact that it doesn't operate based on mood or opinion. When it's right, it works. When not, it doesn't. I still believe that. :)
 

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Thanks Dad, Hey you want a job as my PR guy? My shortness is a long holdover from when my kids were small. They often spoke incorrectlly, and hardly listened at all. I would often speak to them in Loaded sentences, full of double meaning and lots of information, forcing them to think. I like to think I made them better people for the exercise.
This forum is much the same as the Fog's dinner table of the sixties. I'm glad to see another adult joining me.

FOG
 

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How come no one has mentioned port design? Cam profiles? Squish shape? Air velocity at the venturi? exhaust scavaging? Exhaust port shape? Shrouded valve pockets? Guides obstucting the ports?

"Does the stock muffler flow the volume the engine produces at any greater restriction than aftermarket?"
Yes, and yes it has been proved.
"Analyze that, and show me how ANY THEORY you can find changes the fact that it mixes fuel in direct relation to the volume of air coming through it,...."
Direct relation; NO. My carburetors are attached to a device called a throttle, which can change the relationship of the volume of air to the volume of fuel. It can change the volume of air by way of the butterfly valve and it changes the volume of fuel by way of jets and circuits in the carbs. At higher RPMs there is more fuel in a gallon of fuel/air mix than at idle. See, the DIRECT relationship has changed.
Most Exs have CV carbs which will change the fuel/air mix with no input from the throttle. It uses throttle plate vacuum to lift the needle, enlarging the jet opening.
You CANNOT use a vacuum cleaner analogy because a vacuum cleaner delivers a constant vacuum, a motor does not. That lack of constant vacuum is a real problem in tuning.
"...why did FOG use the analogy that it's like changing cam timing.... not that it DOES change it...."
He didn't say it was "like" changing the cam timing, he said it "effectively" changed the cam timing. Not that it was similar but, for all intents and purposes, does change the cam timing. It has the same effect as installing an exhaust cam with a longer overlap.
Now...on to Jet Kits;
I, like FOG have no use for jet kits. BUT I have a decent collection/assortment of jets and needles (as I imagine FOG does). When the bike needs jetting, I have the jets I need. I also have quite a bit of experience in carb jetting, so I have no use for a "Jet Kit" per se. (OK, one of the jet kits sold has a tapered needle that I swear by IF you are running the stock CVs, but it is available elsewhere. It overcomes the lag/flat spot the original post was talking about. Doesn't fix it, just masks the symptoms).
So there are uses for Jet Kits; If you don't have a decent assortment of jets, or when you don't have any experience (or don't want any) in jetting carbs.
Just so we all know, Carbs are adjustable. The adjustment comes from jets and needles. When designing the motor in Japan one of the specs is that it has to run acceptably in Denver (about a mile above sea level) to Richmond ,BC (Below sea level). To get this level of tune there must be compromises and one of the compromises is in carb jetting. To remove this compromise you rejet to YOUR situation.
So which bikes could benefit from a rejet...99.9% of bikes. Is it worth the effort? You decide. I re-jet when the temp changes, when the air density (barometer) changes, as the valves and rings seat in, when the sun shines or doesn't...etc etc etc.
So I will say if you want perfect, learn how to tune. If you don't want to put forth the effort and have no motivation to learn, a jet kit will get you close.
As an aside; Every race bike I have ever bought came with an assortment of jets and needles in the spares kit. (HMMM, a factory "Jet Kit"?)
As FOG says a header will get you one maybe two HP. Cost ~$600 CDN. You can pick up one or two HP by degreeing the cams. Cost ~$25... a jet kit 0 HP. Cost ~$80.
 

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bitzz said:
How come no one has mentioned port design? Cam profiles? Squish shape? Air velocity at the venturi? exhaust scavaging? Exhaust port shape? Shrouded valve pockets? Guides obstucting the ports?
Because those weren't the topic. Jetting was. :)

bitzz said:
"Does the stock muffler flow the volume the engine produces at any greater restriction than aftermarket?"
Yes, and yes it has been proved.
And the resulting HP was....... If you effectively passed more air/fuel through an engine, it WILL make more HP. Emphasis on effectively.

bitzz said:
"Analyze that, and show me how ANY THEORY you can find changes the fact that it mixes fuel in direct relation to the volume of air coming through it,...."
Direct relation; NO. My carburetors are attached to a device called a throttle, which can change the relationship of the volume of air to the volume of fuel. It can change the volume of air by way of the butterfly valve and it changes the volume of fuel by way of jets and circuits in the carbs. At higher RPMs there is more fuel in a gallon of fuel/air mix than at idle. See, the DIRECT relationship has changed.
I'm confused. I said it delivers fuel in direct relation to the volume of air. You say NO?! Are you saying that there's more fuel to air at wide open than fuel to air at idle? If so, you're simply wrong. If not, then you're saying the same thing I did..... because it's right... and a VERY simple concept that fuel burns best at a specified ratio to air. And it's all of those little jets, circuits, and fancy parts that are accomplishing just that.

bitzz said:
Most Exs have CV carbs which will change the fuel/air mix with no input from the throttle. It uses throttle plate vacuum to lift the needle, enlarging the jet opening.
And it has those features, striving to keep the air fuel mixture correct at every throttle position because the venturi alone is too large to handle the full range of flows accurately through one jet. And while we're at it, if you mean it uses manifold vacuum not ported vacuum, you might want to look at that further. I haven't dwelled on this detail too much beyond the basic idea of its function because I was just trying to use it, not design it, but it's NOT manifold vacuum that's utilized.

bitzz said:
You CANNOT use a vacuum cleaner analogy because a vacuum cleaner delivers a constant vacuum, a motor does not. That lack of constant vacuum is a real problem in tuning.
And THAT'S where this discussion belonged all along and IS the source of potential for needing changes. The pulse is effected slightly, IF there's a true change in flow, and the ability of the fuel circuit to respond to those pulses is the real world side of what has the potential to create a problem that the theory doesn't need to account for. In theory it requires NO change, in practice it may. Emphasis on two words, "IF" and "MAY". Depending on the carburetor and the effective range of the change, it may or may not require a change. Experience on these suggests that they're good as is with the exceptions as noted and posted about.

You'll get into overlaps of the circuits, efficencies of the carb design, and find the real world imperfections that never fully realize theoretical perfection at every RPM. It also requires an actual change to require actual attention, also the point of the original discussion. If you've got a problem, it should be able to be tuned out. I've not encountered those problems and HAVE tried larger mains AND shimmed needles, both too fat, and it WAS subtle. I'm back at stock with the pilots out 2 1/2 turns and the 3,000 to 4,000 or so RPM flat spot GONE.

bitzz said:
"...why did FOG use the analogy that it's like changing cam timing.... not that it DOES change it...."
He didn't say it was "like" changing the cam timing, he said it "effectively" changed the cam timing. Not that it was similar but, for all intents and purposes, does change the cam timing. It has the same effect as installing an exhaust cam with a longer overlap.
It seems that you're arguing the definition of a word and in my understanding of those two words in those two examples, they are synonymous. That's the way I read it and used it. If not, I'll let you choose the one that you prefer and just agree with that. And I'd go further to say that the more accurate description is it effectively increases the exhaust lobe duration, but I'd understand the intent either way.

bitzz said:
Now...on to Jet Kits;
I, like FOG have no use for jet kits. BUT I have a decent collection/assortment of jets and needles (as I imagine FOG does). When the bike needs jetting, I have the jets I need. I also have quite a bit of experience in carb jetting, so I have no use for a "Jet Kit" per se. (OK, one of the jet kits sold has a tapered needle that I swear by IF you are running the stock CVs, but it is available elsewhere. It overcomes the lag/flat spot the original post was talking about. Doesn't fix it, just masks the symptoms).
So there are uses for Jet Kits; If you don't have a decent assortment of jets, or when you don't have any experience (or don't want any) in jetting carbs.
Just so we all know, Carbs are adjustable. The adjustment comes from jets and needles. When designing the motor in Japan one of the specs is that it has to run acceptably in Denver (about a mile above sea level) to Richmond ,BC (Below sea level). To get this level of tune there must be compromises and one of the compromises is in carb jetting. To remove this compromise you rejet to YOUR situation.
So which bikes could benefit from a rejet...99.9% of bikes. Is it worth the effort? You decide. I re-jet when the temp changes, when the air density (barometer) changes, as the valves and rings seat in, when the sun shines or doesn't...etc etc etc.
So I will say if you want perfect, learn how to tune. If you don't want to put forth the effort and have no motivation to learn, a jet kit will get you close.
As an aside; Every race bike I have ever bought came with an assortment of jets and needles in the spares kit. (HMMM, a factory "Jet Kit"?)
As FOG says a header will get you one maybe two HP. Cost ~$600 CDN. You can pick up one or two HP by degreeing the cams. Cost ~$25... a jet kit 0 HP. Cost ~$80.
And if you're changing jets for all of the subtle scenarios you outlined, then congratulations. You're chasing fractions of fractions of a problem that's more about the quality of the air you're working with, not the quantity, and you'll never get it all back. In fact, very little unless you're talking LARGE excursions from baseline. If the one of the key components of your air fuel mixture is faulty, you can't make it 100% with tuning and you won't get it all back. If you're racing, neither will your competitor, so relax. ;)

These posts are for practical use of these bikes and once it's running nicely, not stumbling, burbling, or falling flat on its ass, learning to ride it well will get the real results, not chasing a HP or two. And the factory WILL tell you to re-jet if you're continually at elevations like Denver (5,000' or so) and above. I've been there and 5,000 feet matters but 7,000 feet and above will REALLY screw with your performance and CAN benefit from a jet change. That's also a dramatic change in environment from the majority of dry land.

And yes, I DO have more than a little knowledge and experience with this stuff. At the strip, being finicky has some value. At the road track or especially on the street? VERY suspect value. "It's the rider, not the bike." I see it repeated time and again, track after track, thousands of riders, at the seventy or so track classes like I'll be teaching just this year.
 

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dad said:
bitzz said:
How come no one has mentioned port design? Cam profiles? Squish shape? Air velocity at the venturi? exhaust scavaging? Exhaust port shape? Shrouded valve pockets? Guides obstucting the ports?
Because those weren't the topic. Jetting was. :)

Actually no...the topic was buddy bought a new exhaust for his bike and found after he installed them found a hollow spot around 4500-5000rpm that he was interested in getting rid of. If you want to get rid of this flat spot, without detriment somewhere else in the rev band, you better start looking at the ports.
The original post said that he WOULD NOT BE JETTING HIS BIKE. So how the topic got to be jetting, I don't know.


bitzz said:
"Does the stock muffler flow the volume the engine produces at any greater restriction than aftermarket?"
Yes, and yes it has been proved.
And the resulting HP was....... If you effectively passed more air/fuel through an engine, it WILL make more HP. Emphasis on effectively.

Now you want to ADD the word effectively to the question. Plain and simple; every aftermarket exhaust system I have ever seen, for a motorcycle, does offer less flow restriction than stock. Not "effectively" or "like" or "similar to" or "resembling". I said an aftermarket exhaust DOES offer less restriction than stock.
Here is where you are going wrong: If you install a less restrictive exhaust on a motor it WILL take in MORE air, the problem now is the size of the jets can't keep up. Sooooo effectively, you seem to like that word, you will get 0 HP increase until you increase the amount of fuel going in. That is the carb's job.
Tuning is all about BALANCE. You must balance the carbs to the exhaust. One without the other is USELESS.
You asked about flow restriction, not HP gains.


bitzz said:
"Analyze that, and show me how ANY THEORY you can find changes the fact that it mixes fuel in direct relation to the volume of air coming through it,...."
Direct relation; NO. My carburetors are attached to a device called a throttle, which can change the relationship of the volume of air to the volume of fuel. It can change the volume of air by way of the butterfly valve and it changes the volume of fuel by way of jets and circuits in the carbs. At higher RPMs there is more fuel in a gallon of fuel/air mix than at idle. See, the DIRECT relationship has changed.
I'm confused. I said it delivers fuel in direct relation to the volume of air. You say NO?! Are you saying that there's more fuel to air at wide open than fuel to air at idle? If so, you're simply wrong. If not, then you're saying the same thing I did..... because it's right... and a VERY simple concept that fuel burns best at a specified ratio to air. And it's all of those little jets, circuits, and fancy parts that are accomplishing just that.

Try this, (I have): Install an O2 sensor on a carburated bike. Watch the readout as you go through the rev band. You will find that the motor is lean at idle and at full revs and rich in the middle. The richest at the instant the needle comes out of the primary. This has ALWAYS been a short fall with carbs, any carb. Quadra Jets and ThermoQuads have the best metering.

bitzz said:
Most Exs have CV carbs which will change the fuel/air mix with no input from the throttle. It uses throttle plate vacuum to lift the needle, enlarging the jet opening.
And it has those features, striving to keep the air fuel mixture correct at every throttle position because the venturi alone is too large to handle the full range of flows accurately through one jet. And while we're at it, if you mean it uses manifold vacuum not ported vacuum, you might want to look at that further. I haven't dwelled on this detail too much beyond the basic idea of its function because I was just trying to use it, not design it, but it's NOT manifold vacuum that's utilized.

NO NO NO NO, I said throttle plate vacuum. If you used plenum (you call it "manifold vacuum") vacuum the slider would be pegged to the top of it's travel most of the time.
Actually what a CV carb does is keep the flow through the venturi at a CONSTANT VELOCITY to make it easier to tune.
(What is "ported vacuum"? I have never heard this term before.)


bitzz said:
You CANNOT use a vacuum cleaner analogy because a vacuum cleaner delivers a constant vacuum, a motor does not. That lack of constant vacuum is a real problem in tuning.
And THAT'S where this discussion belonged all along and IS the source of potential for needing changes. The pulse is effected slightly, IF there's a true change in flow, and the ability of the fuel circuit to respond to those pulses is the real world side of what has the potential to create a problem that the theory doesn't need to account for. In theory it requires NO change, in practice it may. Emphasis on two words, "IF" and "MAY". Depending on the carburetor and the effective range of the change, it may or may not require a change. Experience on these suggests that they're good as is with the exceptions as noted and posted about.

You have to figure out what throttle plate vacuum is. Your argument would be valid if we were talking about a multi cylinder motor with a shared plenum, but we're not.

You'll get into overlaps of the circuits, efficencies of the carb design, and find the real world imperfections that never fully realize theoretical perfection at every RPM. It also requires an actual change to require actual attention, also the point of the original discussion. If you've got a problem, it should be able to be tuned out. I've not encountered those problems and HAVE tried larger mains AND shimmed needles, both too fat, and it WAS subtle. I'm back at stock with the pilots out 2 1/2 turns and the 3,000 to 4,000 or so RPM flat spot GONE.

bitzz said:
"...why did FOG use the analogy that it's like changing cam timing.... not that it DOES change it...."
He didn't say it was "like" changing the cam timing, he said it "effectively" changed the cam timing. Not that it was similar but, for all intents and purposes, does change the cam timing. It has the same effect as installing an exhaust cam with a longer overlap.
It seems that you're arguing the definition of a word and in my understanding of those two words in those two examples, they are synonymous. That's the way I read it and used it. If not, I'll let you choose the one that you prefer and just agree with that. And I'd go further to say that the more accurate description is it effectively increases the exhaust lobe duration, but I'd understand the intent either way.

Nope not synonymous.
http://dictionary.reference.com/browse/like
http://dictionary.reference.com/browse/effectively
Has the same effect as installing an exhaust cam with a longer over lap. Not "similar", "like" or "resembling". Has the SAME END RESULT. EXACTLY.

"And I'd go further to say that the more accurate description is it effectively increases the exhaust lobe duration..."
Nope, longer duration might or might not get you more over lap. I am talking about "Cam Timing Overlap", the number of degrees of crankshaft rotation that both the intake and exhaust valves are open at the same time.



bitzz said:
Now...on to Jet Kits;
I, like FOG have no use for jet kits. BUT I have a decent collection/assortment of jets and needles (as I imagine FOG does). When the bike needs jetting, I have the jets I need. I also have quite a bit of experience in carb jetting, so I have no use for a "Jet Kit" per se. (OK, one of the jet kits sold has a tapered needle that I swear by IF you are running the stock CVs, but it is available elsewhere. It overcomes the lag/flat spot the original post was talking about. Doesn't fix it, just masks the symptoms).
So there are uses for Jet Kits; If you don't have a decent assortment of jets, or when you don't have any experience (or don't want any) in jetting carbs.
Just so we all know, Carbs are adjustable. The adjustment comes from jets and needles. When designing the motor in Japan one of the specs is that it has to run acceptably in Denver (about a mile above sea level) to Richmond ,BC (Below sea level). To get this level of tune there must be compromises and one of the compromises is in carb jetting. To remove this compromise you rejet to YOUR situation.
So which bikes could benefit from a rejet...99.9% of bikes. Is it worth the effort? You decide. I re-jet when the temp changes, when the air density (barometer) changes, as the valves and rings seat in, when the sun shines or doesn't...etc etc etc.
So I will say if you want perfect, learn how to tune. If you don't want to put forth the effort and have no motivation to learn, a jet kit will get you close.
As an aside; Every race bike I have ever bought came with an assortment of jets and needles in the spares kit. (HMMM, a factory "Jet Kit"?)
As FOG says a header will get you one maybe two HP. Cost ~$600 CDN. You can pick up one or two HP by degreeing the cams. Cost ~$25... a jet kit 0 HP. Cost ~$80.
And if you're changing jets for all of the subtle scenarios you outlined, then congratulations. You're chasing fractions of fractions of a problem that's more about the quality of the air you're working with, not the quantity, and you'll never get it all back. In fact, very little unless you're talking LARGE excursions from baseline. If the one of the key components of your air fuel mixture is faulty, you can't make it 100% with tuning and you won't get it all back. If you're racing, neither will your competitor, so relax. ;)

Yes I rejet that often, but then so do my competitors, and YES at that point I am looking for that last HP.
I have a problem with "more about the quality of the air you're working with, not the quantity". I deal with quanity, as I have no idea on how to change air "quality". Maybe you could enlighten me.


These posts are for practical use of these bikes and once it's running nicely, not stumbling, burbling, or falling flat on its a$$, learning to ride it well will get the real results, not chasing a HP or two. And the factory WILL tell you to re-jet if you're continually at elevations like Denver (5,000' or so) and above. I've been there and 5,000 feet matters but 7,000 feet and above will REALLY screw with your performance and CAN benefit from a jet change. That's also a dramatic change in environment from the majority of dry land.

The Factory will tell you to rejet in those circumstances because using stock jets at that altitude will mean the motor is SO lean that it will burn the valves, resulting in a WARRANY CLAIM. The factory doesn't really give a flying **** how well your bike runs or doesn't. Always keep in mind the manufacturers mantra " Death before warranty"

And yes, I DO have more than a little knowledge and experience with this stuff. At the strip, being finicky has some value. At the road track or especially on the street? VERY suspect value. "It's the rider, not the bike." I see it repeated time and again, track after track, thousands of riders, at the seventy or so track classes like I'll be teaching just this year.

"At the strip, being finicky has some value. " Only if you put value on winning races...and that is why I enter races. I LIKE TO WIN. If I didn't I would go to track days. It is real easy to look like a hero at MOST track days...even on an EX500.
This isn't a pissing contest. I am old with prostrate issues.
I think my point was that adding stuff to the outside of an EX isn't really gonna get you anything. Jet kits, headers and the like are alot like pissing up wind. There is NO short cut to performance gains and as evidenced by the original post you can easily screw yourself without knowing what you are up against.
or
it is alot easier to lose HP than gain it.
...and I still maintain the best bang for your buck would be to degree your cams.
 
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