I'm riding a 1990 KDX200 with PC pipe and silencer and airbox mod. In Tallahassee it's 70-80 degrees with high humidity. My mixture is 35:1 and jetting is 38 pilot, cel 2nd from top and 152 main. The question is regarding a mid throttle bog at what I would guess to be at 3 to 4 thou. rpm. I was thinking about going to the middle clip, but wonder if lowering the float from 17mm to 16mm might have an effect?? Or should I go with a bigger slide cutaway? Whan I'm on the pipe it will stand up in 4th gear. It's run running great, but I'd like a little more control at lower rpm's. Thanks, Jay
float vs jetting question
- Thread starter cicone
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If your float height was causing you problems at mid throttle, and at certain RPM's, then it would cause problems at other positions and other RPM's as well. As far as I know the float has a predesignated setting that should stay the same.
I would look at jetting or other things. I'm not an expert on the float height thing, I just never heard anyone ever mention adjusting to anything besides factory spec.
Does your bike have a KIPS valve or exhaust valve? The tension on my exhaust valve spring has a very dramatic affect on mid rpm performance. I have set it back from factory 90 degrees to 45 degrees in the past and it ran a lot flatter at lower RPM's.
The main jet on my PWK will affect lower circuits too.
Hope you find a solution!!!
Joe Chief
I would look at jetting or other things. I'm not an expert on the float height thing, I just never heard anyone ever mention adjusting to anything besides factory spec.
Does your bike have a KIPS valve or exhaust valve? The tension on my exhaust valve spring has a very dramatic affect on mid rpm performance. I have set it back from factory 90 degrees to 45 degrees in the past and it ran a lot flatter at lower RPM's.
The main jet on my PWK will affect lower circuits too.
Hope you find a solution!!!
Joe Chief
Sounds like the clip on the needle needs to be moved up one notch. Raising the clip will lower the needle which will lean your mid range a bit. Cutting the slide is not highly recommended by me, basically you are changing the entire range of the working of the carb as it relates to jetting. Not saying it won't work, but be prepared to change the pilot jet, main jet and needle jet.
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- #5
Weekend results: lowering one clip made it worse and confirmed suspicions. Went to top clip and mid range pulls beautifully--however it seems that I've now lost much of the over rev---could be psychological in that the midrange pull is so strong that when it gets on the pipe the transition isn't as abrupt. I like the smoother delivery of power anyway. Jason, to answer your question about other jets sizes---have tried bel, bek, cek, cel(the best so far). 38 pilot seems to work better than 40, 42, 45 and I believe took out the 155 main and replaced with 152??. Do you think some tinkering with main could give me some more top end? Thanks, Jay
canyncarvr
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- Oct 14, 1999
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Would you agree that the term 'flat spot' would be better applicable than 'bog'?
That would make some sense.
Float height does effect overall jetting...the further the fuel needs to be 'pushed' (lower float level), the more lean the overall mix will be. It's not generally a tuning device. I changed mine (lowered 1mm) to improve bike continence (less peeing).
re: 'could be psychological..'
Good call. Good chance.
Still, you can make a huge difference in the upper power band with a main jet change of a single size. Well.....works for me! ;)
Cutting the slide will not effect the 'entire' range of the carb. A leaner cut (the 'H' models have a 5mm oem slide...I think you might have a 6mm already?) and jetting to suit will indeed improve your bottom-end response AND the transition to the larger diameter needle you're using.
A 6mm cut slide has good reviews with the CEL. A top-clip choice on a 38.15-L1 sounds a bit unusual...but I suppose the high RH would effect that.
Sounds like you're on the right track!
That would make some sense.
Float height does effect overall jetting...the further the fuel needs to be 'pushed' (lower float level), the more lean the overall mix will be. It's not generally a tuning device. I changed mine (lowered 1mm) to improve bike continence (less peeing).
re: 'could be psychological..'
Good call. Good chance.
Still, you can make a huge difference in the upper power band with a main jet change of a single size. Well.....works for me! ;)
Cutting the slide will not effect the 'entire' range of the carb. A leaner cut (the 'H' models have a 5mm oem slide...I think you might have a 6mm already?) and jetting to suit will indeed improve your bottom-end response AND the transition to the larger diameter needle you're using.
A 6mm cut slide has good reviews with the CEL. A top-clip choice on a 38.15-L1 sounds a bit unusual...but I suppose the high RH would effect that.
Sounds like you're on the right track!
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- #7
canyoncarver, I don't think I would have called it a bog---more like four stroking until rpm high enough to light up the pipe. One thing still puzzles me. The 38 pilot seems much smaller than what people are recommending and my air screw still seems to have little effect. The carb diagrams show a spring on the a/s---but I assume it will fully seat with or without it. The carb's been cleaned countless times. Yesterday it ran great. Should I leave well enough alone or do you have any additional suggestions. Much appreciated, Jay
canyncarvr
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Under the heading of 'Words Mean Things' what we have here is a '...failure to communicate.' :think:
If it's indeed 4-stroking (a rich burble..firing every other time like it (maybe) does with the choke on after a cold-choke start?) that is of course opposite from a lean bog (falling-flat boo-wah sound).
I don't see a 4-stroking issue going on unless you're referring to a 'happy 2-stroke' skipping, 4-stroking that you'll get at most any throttle position short of WOT under no load.
But that wouldn't be a bog thing.
As chief said, it's throttle position that indicates carb circuit in use, not rpm.
So, if you're at 1/4 throttle and roll thru 1/2 throttle under load the bike stutters in the 1/2 throttle area?
The bike should not idle with the AS closed..or at least stutter and goober like it's going to die any second. Well, given that the slide is all the way down...which is where it should be to check the pilot circuit.
What does your AS do in such a case?
If it's indeed 4-stroking (a rich burble..firing every other time like it (maybe) does with the choke on after a cold-choke start?) that is of course opposite from a lean bog (falling-flat boo-wah sound).
I don't see a 4-stroking issue going on unless you're referring to a 'happy 2-stroke' skipping, 4-stroking that you'll get at most any throttle position short of WOT under no load.
But that wouldn't be a bog thing.
As chief said, it's throttle position that indicates carb circuit in use, not rpm.
So, if you're at 1/4 throttle and roll thru 1/2 throttle under load the bike stutters in the 1/2 throttle area?
The bike should not idle with the AS closed..or at least stutter and goober like it's going to die any second. Well, given that the slide is all the way down...which is where it should be to check the pilot circuit.
What does your AS do in such a case?
As to Jay and the pilot/a.s. dilemna, If my pilot is too small I can always choke it off with the a.s. which is only considered a fine tuner for the pilot, (credits to RMGUY) but it always runs nicer w/ the right pilot in there where you can set the a.s. to within recommended specs. Snappy right on the get go. I've seized pistons because of too lean pilot. Reason being you can be at 10,000 or more rpm at 1/8 throttle just maintaining speed.
Canyn,
That happy burble, I HATE IT!!! I've tried just about everything to lessen it. I know older bikes run a lot smoother. My bike is the biggest burbler I've ever been on!!! I will be installing new reeds (dual stage) this winter, and hope they will help. What are your thoughts on this please??
Joe Chief
Canyn,
That happy burble, I HATE IT!!! I've tried just about everything to lessen it. I know older bikes run a lot smoother. My bike is the biggest burbler I've ever been on!!! I will be installing new reeds (dual stage) this winter, and hope they will help. What are your thoughts on this please??
Joe Chief
canyncarvr
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'Happy' is a good thing!
IMO and all that other disclaimer junk...but if your bike doesn't ever do that, it would be too close to too lean for me!
tu-tu
Think good thoughts! It's like 'hating' the uneven idle, pressurized manifold of a 106º centerlined, 300º duration V-8 cam.
IMO and all that other disclaimer junk...but if your bike doesn't ever do that, it would be too close to too lean for me!
tu-tu
Think good thoughts! It's like 'hating' the uneven idle, pressurized manifold of a 106º centerlined, 300º duration V-8 cam.
