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Discussion Starter · #1 ·
So this project bike I've made some posts on I'm near the final bits now. I also really suck at tuning carbs, and am making my best guess below at what needs done, but I'd like to make sure via some insight from those of you who are way better at this.

It came with a Yoshimura 2=>1 exhaust, so if I had the choice and a free stock exhaust...I'd go stock. But, alas, here we are.

I have:
Cleaned the carb and replaced all o-rings via Duc's kit
set mixture screws at 2.5 out
replaced the main/pilot jet from the dyno kit jets back to stock 130 and 35 main/pilot This was from a 126/35
Fog Mod on air box
I did not have a stock needle at the time, left the dyno-needle at two clips down ( Think this is the issue, quite a lot of lift, equiv of like 6-8 of those washers, lol )
checked and adjusted valve clearances
Synced at 4k RPM

This is my procedure for my stock 500 which runs fine, this one is not though..
Everything that I'm experiencing tells me too rich:

  • Bike smells crazy rich
  • Will start without choke fine
  • Full Choke will almost kill it if flipped quickly
  • Chugging response, even a slow pull doesn't have the grab that my stock one has
  • Snapping to WoT is laggy response, kind of lugs doesn't have any getup and go if you will, if im real slow onthe throttle it'll go, but not well


My guess is the clipped needle is allowing way too much fuel in, so I'm about to pull the carb and put stock needles in. However, is there anything I should look at with a setup like this?

Appreciate any insight or confirmation, I'm trying to get better at diagnosing and fixing mixture issues.

Edit:

Almost forgot to include, it seems to idle just dandy!
 

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most probably the wrong needles. it's not just the needle height but the profile if it's thinner at the top (when the slides are closed) it will idle rich also the transition from the pilots will be rich. most likely why it stinks rich. but if the lower to middle sections are also thinner it will run rich and choke up higher up the rev range. 2 and half turns out is the start point for stock needles and jets. may need to shut them way down and drop the needles to the lowest clip (until the stock ones are fitted) until you get the right needles and set it up as stock the only way to configure carburation is by experimenting and watching the results.
there is an ideal fuel to air ratio though out the whole rev range from idle to WOT but I can't remember what they are not that it matters you will have no way to read them anyway. even using stock setting and tweaked the EX tends to run a little rich at WOT. and is the reason for the airbox mod. you will have to do a final pilot screw adjustment in any case. so worth a shot moving the settings for now.
 

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Discussion Starter · #3 ·
Thanks yorkie! Just got OEM needles in, need to get everything back together and sync and test then. I'll post back with where it is after that...

However, It's a little late. Don't want the neighbors making any phone calls from me syncing the carbs at this hour so I'll have to do it tomorrow. Haha.
 

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How is your float level? Did you set the float heights in the carbs. And more importantly, did check the fuel level height with the carbs installed on the bike? This can be done via some clear plastic tubing attached tot he float bowl drains.

The height of the fuel in the bowls can cause rich or lean, and this first base measurement is critical to all other aspects of tuning the carbs.
 

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Discussion Starter · #5 ·
I did check the float heights dry when i had them out and they seemed in check at 17mm but as i go to pull it off here again i'll check it wet before i do that.

So stock needles helped a lot, but it's still pretty rich, brought the mixture screws down to about 1.75 and still seems rich, half wondering it the 126 jet was really in there for a good reason now. Lol.
Can't get the bike to response the way it should, still just a little off on the throttle response.

I'm going to check the bowl height wet, not sure if i should try the 126s or not. I didn't really think an aftermarket exhaust would need me to deviate that far away from stock, but I'm not sure.
 

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it shouldn't I have a Motad 2 into 1 aftermarket pipe on mine. completely stock settings runs fine. in fact it runs so well sometimes I can't believe it's 32yo and has 88k on the clock. yes occasionally when starting from cold it smells a little rich but a 15mins blast to warm it up has it running perfect once more.
do check the float levels wet it can effect the pilot circuits. needs to be on the float bowl join + or - 1mm mines on the low side of that. and perhaps a run to warm it through will help, once it has been run up to temp. you will have to tweak the mixture screws. and perhaps adjust the idle.

edit. the procedure for that and getting it spot on is on the forum somewhere.
 

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Discussion Starter · #7 ·
Okay, so in the middle of wet testing which I never did before..And I think I see why I should now. I've never done this so kind of a no stupid questions moment here hopefully...

Both of these look really high to me now that I see it with actual fluid. I had difficulty getting a clear image on the right side (as mounted) but the left side pic shows pretty clearly what I'm seeing.

54427
54426


These look too high right? Or should I do this off the bike too? These almost look high enough to me that they'd just about be pouring into the intake.
 

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I did check the float heights dry when i had them out and they seemed in check at 17mm but as i go to pull it off here again i'll check it wet before i do that.

So stock needles helped a lot, but it's still pretty rich, brought the mixture screws down to about 1.75 and still seems rich, half wondering it the 126 jet was really in there for a good reason now. Lol.
Can't get the bike to response the way it should, still just a little off on the throttle response.

I'm going to check the bowl height wet, not sure if i should try the 126s or not. I didn't really think an aftermarket exhaust would need me to deviate that far away from stock, but I'm not sure.
Those 126's are main jets and have zero to do with rich idling. They only come into play as throttle is 3/4 to full.

The 250 I have been tweaking lately also had a rich idle. To get the fuel height in the bowl correct I had to increase float height to 19mm, which effectively lowers the floats and reduces the amount of fuel in the bowls. Then when the fuel height was right around level with the joint between carb body and float bowl I could start using the A/F screws to get things where I wanted.
 

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Okay, so in the middle of wet testing which I never did before..And I think I see why I should now. I've never done this so kind of a no stupid questions moment here hopefully...

Both of these look really high to me now that I see it with actual fluid. I had difficulty getting a clear image on the right side (as mounted) but the left side pic shows pretty clearly what I'm seeing.

View attachment 54427 View attachment 54426

These look too high right? Or should I do this off the bike too? These almost look high enough to me that they'd just about be pouring into the intake.
They are SUPER high! Like Cheech and Chong "Up in Smoke" high.... :)
 

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Discussion Starter · #10 ·
Okay sweet, I was also kinda like "Damn, I think this is way off" I'm going to pull them and try and get this in spec, should be just at where the bowl joins right? Thanks for all the quick replies here. I think I dry checked them at 17mm.

Also any tips for wet checking off the bike, can i just tilt them to mimic it and the do a final check on bike?
 

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Here's an ex-500 thread with a picture from our very own ducatiman. See the correct fuel height in his picture.



When you take the carbs off next and adjust, do the wet test and get them right before spending all the time to refit them to the bike.
 
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Discussion Starter · #12 ·
Awesome, thanks for that link. I feel like I've been having a hell of a time finding old posts, i've only been on the new forum for awhile now after along hiatus but keep hitting dead links.
 

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did anybody tell him to junk that jet kit and replace all stock parts. Then with the FOG MOD and tuned pilot screws it will run fine. the FOG MOD was especially designed to cure top end richness

FOG
 
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Discussion Starter · #14 ·
Yep, also realized i wet tested on bike with the rear jacked up, on bench they are actually under by about 1/4". Should the floats be set wet on a bench flat or one that mimics the bikes carb position?

And @fog, I have junked all after market jettings etc, unless the needle holder wasn't OEM, I replaced the main jet and pilot jet with 130/35 respectively.

It came with 126/35, and a 2 clip down dyno needle that was shimmed with two washers. ( Washers that i also removed )
 

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just a quick point if the levels are that high (with the bike jacked up) then that is the level they are running at also jacked up. I maintain the correct levels are when the bike is upright (not on side stand) and sat with both wheels on the floor on level ground and tested on the bike. however for convenience they are best set off the bike. wet tested while level. purely because of the hassle having to remove them every time you need to do adjustments. then check the levels on the bike once set.
 

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Discussion Starter · #16 ·
Well after much fiddlin' around, got the floats back to 17mm flat from the lip and 19mm on a tilt with the valve just sealing, not sure how the manual actually measures'm but my manual says 17+-2mm so think I'm safe. Wet tested on bench to just a hair below the seal. Tried both 126 and 130 main jet, 126 was too lean as I imagined, but figured id test it after the float fix, put 130's back in let it warm all up, synced at 3k this time instead, of 4k.

I also poor man removed the pair for now (Tubes together, sealed airbox, capped the carb), gonna order a plate kit, but it sounds so much better without all the spittle backfiring from it so i refuse to put the pair back on while I wait for it.

You can listen here if you're curious. Vid goes Snap WOT, 4k, 5k, 7k, blip, done.

This is fully warm, choke off. Idles at around 1250, chokes up to 3k on full. I think it's still a bit rich, but I think I'm gonna leave it here. Scouring the forum found someone saying their ex500 smells a bit like a go-kart you'd find at Disney world. That about sums up the richness here I think...However, If anyone hears anything in the vid you think I should immediately care about let me know. I just did clearances a few days ago as well.

I have yet to try riding it, and probably still need to tune the mixture screws but I think it's at least getting somewhere now. I've had the carbs off this thing more than I'd ever like to but I think I've learned a good bit on'm along the way.

I"m gonna go throw the tank back on and try it out to see where it is.Probably actually ride it a bit see if I get ~45-50mpg or so. if so then im done screwing with it. Other than waiting for tires to come in that is.

Thanks to everyone here's input. Makes learning this stuff a hell of a lot easier with a whole group of mentors and good folk.
 

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sounds fine to me. you will find out if it's right when it's on the road. clear path. wind it on hits 6k then takes off like a rocket and screaming like a banshee. yup you fixed it.
 

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Discussion Starter · #18 ·
Thanks for all the help! I did take it for a quick spin, only around the neighborhood so I couldn't really wind it up..It also has 18 year old tires on it I don't trust at all ( They passed inspection, humorously) . Waiting for a rear to get in. None the less felt pretty good just buzzing around from 1st to 3rd, but i'll be winding it up here as soon as I get trustworthy tires on it.
 

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Exhaust changes also mess with the tuning. A lot. Look up "reversion pressure" as part of tuning. It needs some back pressure. Not as much as stock, but more than most straight through pipes. Have you re-packed the can? You could also try experimenting with a baffle slipped into the can - not to completely stuff it up, but just enough to get the reversion pressure closer to optimum. With a too-open exhaust, some of your mixture is blowing out the exhaust port during cam overlap.
 
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