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Discussion Starter · #1 · (Edited)
Before I get flamed, here’s some background on my bike:

ex250 frame with a sidecar, just swapped a 500 motor after melting a piston in my 250 coming back to San Francisco from Colorado.

a few years ago I bought two 500 motors for $50, one a fresh rebuilt race motor, one a used race motor. No other background. The used one had a timing advancer that I removed. It also had one step colder plugs (that I just swapped for regular ones now).

Because the bike didn’t come with carbs, I got some from an ltd454 with pod filters on eBay. It was re-jetted for the pod filters.

The carb was fitted with:
145 main jet
40 pilot
4 thin shims under the stock needle
Pilot screwed out 5 times

my exhaust is a home made 2-1 into a 1.75” pipe to a gsxr1000 exhaust can.

So enough with the background. I basically need help getting rid of the mid throttle from leaning out. my WOT is running around 13.2, a bit leaner than I’d like, but not terrible. My lower rpm just cracked throttle is pretty rich around 10.8-11.3 coasting, and accelerating It’s 12.5. It’s just that 1/3 throttle at mid rpm where I run super lean.
My bike is slammed, and I likely don’t have room for a traditional air box. I have an AFR gauge, so I can see exactly what’s going on.

Before I ran the bike, I turned the pilot screw back from 5 turns to 2 and it still was a little rich. I’ve since leaned it out even more to around 13.8 afr. it’s even less happy around that mid rpm, so I think whoever tuned it gave up on the idle, and just ran it rich to make that mid range happy.


I just put on about 6” of hose/tube onto the end of my carb to have a makeshift intake manifold with the filter on the ends. I didn’t notice much of a difference, but I didn’t let the bike warm completely up. I currently have the carbs out, I’m going to see what the floats are set at, then put it all back together and see what It’s like at speed.

I’m thinking maybe I could get a 2-1 pod filter (k&n part rc3510 ). I ran a similar one on my ninja 250 engine for 3 years and it did good for evening out pulses and made tuning easy. I found one with the same diameter as my pipe, and I could run it with a bit of the extensions I made to hopefully reduce some turbulence

Thoughts or suggestions? I know the jetting is big, but I’m not going lean up until I can get this mid range under control.
 

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flaming heck, good luck. couple of thoughts, those carbs are smaller than the stock ex500 ones and flow at a lower rate (32cfm) than the ex 500 (37cfm) also have weaker springs and smaller slides so flow is somewhat restricted.
jets are are way too big for the carbs and the needles have a richer profile.
to my knowledge no one running pods have ever proven they eliminated the hole at the transition point from idle to mid range many have tried and failed, get one point right it then leans out somewhere else.
you have a job on your hands there for sure.
I did read once somewhere that some sort of partial success was achieved by drilling the slide holes to 3mm and using much stronger slide springs although I have no idea which springs were used, mostly any info on running pods is very scarce, if anyone did crack it they seems to avoid revealing how and mid way stopped answering questions when asked.
 

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Discussion Starter · #3 · (Edited)
I had no idea the carbs were different, I would have gotten the bigger ones had I known.

And yeah I’ve got myself a project for sure. I’m hell bent to make this work, but I’m hoping some kind of airbox or 2-1 filter will help.

the jetting is for sure big, but My WOT AFR is happy, and it totally rips. drilling out slides and changing springs sounds like a hell of a project. I may try to play with needle tapers, I have one set in a rebuild kit I bought. I’ll also look and see what slides and springs cost, do you know if EX500 slides work with en450/ltd454 carbs?

Edit:
Just took a look, and the EX500 needle that came in my kit is massively different than the ltd454. The 500 is shorter, and has more taper. I also pulled out my ex250 needles. They have a tiny bit more taper down the middle 1/3 of the needle, but at the bottom they reduce in diameter a lot.
I’m going to try to find another slide setup with spring so I can experiment with drilling it out and cutting the spring. Having an AFR gauge is going to be a lot easier than reading plugs.

I’ll post up when I have some results, either good or bad.
 

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Discussion Starter · #4 ·
Okay, I went through the carbs and set the float height. Then I installed the ex250 needles. They’re significantly different than the 500. I put them in with no washers/shims instead of the 4 that were in there before.
I only did a quick ride down the street, and again, the engine was cold, but here’s what I saw:
My idle was about the same. Just before I had messed with these I had given it half a turn more fuel at idle, bringing it from 13.8 to around 13.3. My partial throttle cruising was leaner, around 13.0, up from high 10’s to 11’s . Accelerating at low rpm was leaner around mid 13’s instead of low to mid 12’s. And for the 1/3 throttle where I normally saw 16.5ish (if the engine didn’t cut in and out from lean) I saw high 14’s to low 15’s. A huge improvement.
I’m going to throw a couple shims under the needles before I do another test tomorrow and bring it up to temp. I’ll make sure I do some full throttle runs to see if my AFR has changed up top.
 

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hi sorry for the delay (Europe time zone) I believe the carb bodies are physically the same size but the Venturi profile is different to accommodate for the lower capacity of the 454 engine, whether this will help or hinder the set up is unclear.
you seem to be getting somewhere with it just trial and error from now on.
 

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Discussion Starter · #7 · (Edited)
Some success!
I threw in 3 shims this morning just to see what happened. I also closed up my idle screws half a turn.

My idle is now right around 14, maybe a tiny bit less.
My partially cracked throttle is a little choppy, I think I’m running too rich in that area.
my lower rpm low throttle is around 10.5-11, too rich for sure.
Mid throttle where it use to bog tapers down to around 12.5 or richer
And WOT is hard to tell because I exceed the speed limit quickly, but it seems to be around 11.9-12.5

I have no lean dip at all anymore. I am running overall too rich. I may swap in a 140 main, since it’s easier than removing a needle shim. But I’ll do a freeway run after work before I decide.

Does anyone know what the stock hole on the slide is? Mine is 3mm, and I think it may have been drilled out.

I really think this ninja 250 needle has solved my mid range dip. I’m really excited that it was that easy to solve - assuming it is actually solved.
 

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Discussion Starter · #10 ·
AFA needles are concerned, I'd think 5 or 6 position "jet kit" needles would offer more options. I'd suggest to look into Dynojet or Factory Pro versions. But hey, whatever makes you happy.
I’ll check them out! I’d consider myself moderately novice when it comes to carbs, so I don’t even know what’s out there. These needles that seem to be working is purely luck.
 

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Discussion Starter · #11 · (Edited)
Okay I think I found the right compromise with jetting. I just drove it around and the only time I could get it to run lean is for about 1-1.5 seconds, when I tip into 1/3-1/2 throttle between 4-5,000 rpm. It leans to around 14.5, but quickly corrects itself. I think I maybe saw it stay there for 2 seconds while over geared/uphill, but I really had to set it up to make it do that.

Lower or higher rpm with 1/3-1/2 throttle still sees a brief lean out, but the AFR never goes leaner than 13.9, and it’s for even less time, maybe 1 second max. Giving it more than half throttle does not make it lean out.

Current running conditions are
Idle 14.0+/-
Coasting (low, med, and higher rpm) 12.5ish AFR
Accelerating low 11.8-12.2
Accelerating medium 12.5-13.2
Accelerating high rpm WOT 13.2 (richer at lower rpm WOT)

*it’s hard to look at my gauge and drive through traffic. I may update this if I see something different later.

Current jetting
140 main (down from 145)
40 pilot
1.5 screws out idle
2 shims under needles
Ex250 needle (n16i)
3mm hole drilled into slide (not by me)
Slide and spring are from an ltd454/en450

I attempted to run it with 3 shims and a 140 main, but it ran very rich still. I didn’t know one shim could make such a difference.

I’m going to run the jetting like this for a couple weeks and see how much I like it. I’m also going drag racing Wednesday, I wanna see if I can dip into the 13’s, I’m kind of a brick at speed, and have only managed to do 100mph so far.
 

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Welcome! Any description of "500 race engine"? Compression? Cams? Head work? Stock EX500 carbs are, as we find out, the best (with OEM airbox (7 liters internal capacity) and will support as much HP as the engine will ever make. They are dead simple and I cannot fathom all of the problems folks have with them.

Smallish carbs on big engines have their own tuning challenges. This fellow put a lawn mower carb on a V8 Ford Maverick and got 40+ cruising MPG.

 

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Discussion Starter · #13 · (Edited)
Welcome! Any description of "500 race engine"? Compression? Cams? Head work? Stock EX500 carbs are, as we find out, the best (with OEM airbox (7 liters internal capacity) and will support as much HP as the engine will ever make. They are dead simple and I cannot fathom all of the problems folks have with them.

Smallish carbs on big engines have their own tuning challenges. This fellow put a lawn mower carb on a V8 Ford Maverick and got 40+ cruising MPG.

I wish I could tell you more.
the race engine is a fresh rebuild, and lots of the engine is safety wired, it had a new/rebuilt flywheel with magnets, and that’s all I know. The used engine had a 5 degree ignition advance that I removed, and a few things safety wired. I’ll have to see if the plugs on the race motor are different or colder like the used motor was.
they were both $50 so I didn’t ask too many questions.

I had no idea the carbs I bought were smaller, or else I would have paid more for ex500 carbs. As far as problems with not using a stock airbox, I can’t use one, and never had one, and never will.

I am happy how it’s running now. Aside from looking at the gauge and nitpicking how the AFR changes, It drives great! I do have a random misfire at idle, but I have a feeling my 250 coils and wires that have over 100,000 miles on them might be the issue. I might also do a compression check soon too.
Now that I think about it, I never did a valve adjustment either…

Now that it’s running okay. I need to get back on my mid engine turbo Subaru drivetrain vw bug with nitrous project. There’s a couple events coming up I want to attend, and it needs a tune before I go doing 400hp burnouts.
 
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