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Post by Fox on Mar 15, 2015 8:55:48 GMT -5
Float level set too low? Water in the gas tank? Since it's only happening occasionally I'm thinking maybe you should start looking at possible mechanical or electrical things that could cause an intermittent hiccup. Loose wire connector on the coil? (intermittent spark loss) Loose wire connection somewhere else? Spark plug cap going bad? (intermittent spark loss/spark jumping from cap to head) Bad plug wire? (intermittent spark loss/spark jumping from wire to frame) Valve clearance too small? (compression) Try larger gaps so valves open later and close sooner. Weak valve spring(s)? (compression) I tried a BBK one time and one time only. Ran great for a day and after that it gave me nothing but bogging and more bogging. After a few days of trying everything I know I finally decided the BBK was bad. Put my 50cc jug back on and rode that scooter for another trouble free year.  |
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Post by humanshield on Mar 15, 2015 9:56:34 GMT -5
albongo Ever since I installed my 50mm BBK, I've haggled with this problem. Seems sometimes I can all but eliminate it then one small adjustment and it comes back. One difference is that I never have the problem at FULL throttle (on the main jet). I have a thread on this exact same issue here.... Snorking, gasping Scooter linkRight now I can bog the engine to the point of quitting under the following circumstance.... Cruising perfectly at around 35 (on the main jet) Reduce throttle so that it JUST BARELY maintains that speed or begins to slow just a tiny bit. Engine begins to bog heavily as if the spark is gone. If I maintain that throttle position, the scooter will continue to lose speed until it finally dies. I've tried to think about what's actually happening when this occurs. As I begin to close the throttle, the VACUUM in the carburetor rises because the piston is still moving at nearly the same speed. If that was the case, the additional vacuum "should" cause extra fuel (too much) to be sucked into the stream causing a momentary over rich condition. Again, a larger carb should help with that if I'm correct. If this is true, the engine simply can't breath. But I'm not sure. Top speed ever was 41.72. Seems I should do better if everything else is good with a 50mm piston to me. Another way to check this is to "T" in a vacuum gauge with a hose long enough to be able to watch it while riding. I'm going out today to LET it die then do a plug reading. I suspect my Pilot jet may be too small since it never bogs at 3/4 throttle or more OR...I need a TRUE 20mm carb so the engine can get the volume of air it needs because I suspect the 18mm carb may be too small for the bigger piston. (I never have gained the performance difference I think the 50mm piston should have given even though at one point I thought it did but that was probably because I was used to it running so poorly). Right now I'm running a 95 main jet and a 35 pilot jet with a 50mm piston. I'm a bit surprised you're having this problem with a 72cc kit. I've tried 3 different carbs and none eliminated the problem, but it was less noticeable with one. Have re-checked the valves Changed the coil and CDI New spark plug New Plug Wire assembly Tried raising and lowering the needle (at some settings it's not as bad. Others MUCH worse). Various float level settings I'm still not exactly sure why it does this. I hope to get a better idea today after I do a plug chop (weather permitting) |
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Post by albongo on Mar 15, 2015 12:46:39 GMT -5
Ok I changed the CDI, still happens.
Changed the coil, still happens.
Light is fading and it's starting to rain so tomorrow (hopefully) I'm going to check valve clearance. Because I have to strip the body work to do this I'm going to check the wiring as well. If I can get to the shop I'll get another spark plug to eliminate that.
Humanshield it does feel like a hiccup but it only happens occasionally at WOT the rest of the range feels fine.
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Post by humanshield on Mar 15, 2015 15:06:12 GMT -5
Mine WAS doing at WOT at one time but now it's moved down the throttle range a bit.
I think as you make changes it will move. Did your kit happen to come with a new cylinder head?
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Post by albongo on Mar 15, 2015 15:34:22 GMT -5
No new head with the kit. I stuck with stock head.
I can't seem to nail down when it happens.
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Post by humanshield on Mar 15, 2015 15:35:51 GMT -5
Im sending you a PM Albongo
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Post by albongo on Mar 15, 2015 15:50:04 GMT -5
Got it, made me laugh!
Thanks it's been a trying day.
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Post by humanshield on Mar 15, 2015 16:52:40 GMT -5
Well, I had a slight suspicion that a valve might have been sticking or something like that but now I doubt it since I can reproduce the symptoms. Haven't had a change to do the plug chop yet. Still hoping to today but it's getting late.
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Post by albongo on Mar 16, 2015 16:03:54 GMT -5
I managed to get another CR7HIX NRK Iridium plug today. I stripped the rear body panels off the scoot and checked the valves. Exhaust was .004 and I tightened the in intake from .004 to .003 I changed the spark plug and up jetted back to a 90MJ. I took the scoot for a spin and the cough at WOT was gone.  It does stumble around 1/2 throttle now!  I'll adjust the needle jet and check tomorrow Night. |
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Post by humanshield on Mar 18, 2015 17:37:28 GMT -5
May not help in your situation but today I opened the misture screw another turn and a half and it seems to have resolved my last issue.
Scoots running about as good now as ever.
Have you tried adjusting the mixture? My plug seemed a bit light so I decided it needed a bit more fuel.
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Post by humanshield on Mar 20, 2015 15:02:20 GMT -5
Hey Al,
My scoots really been doing well lately. But....
Yesterday I gassed up at a off brand gas station and as soon as I left I started getting MUCH worse performance. Boggin, stalling etc. So drained ALL that gas out and refilled with Chevron.
Guess what? Smoothed out again like a charm.
I guess my point is make sure you are using a very good quality gasoline because these scoots are pretty sensitive to the fuel they're burning. At least that was my experience yesterday.
YMMV
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Post by albongo on Mar 22, 2015 11:28:43 GMT -5
Thanks for the advice humanshield. I have adjusted the a/f mix, intake valve and given the carb a deep clean using carb cleaner. I think I have fixed the main problem!  There is a very small backfire type sound when letting off from WOT but I think I can eliminate that with more carb tuning. Managed to ride the scoot to work and back everyday this week! |
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Post by niz76 on Mar 22, 2015 12:05:42 GMT -5
Sounds like u almost got it! A backfire is usually an indication of an air leak somewhere. Check the usual places and the exhaust manifold for leaks. RIDE ON!!
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Post by humanshield on Mar 22, 2015 12:56:48 GMT -5
Good Job Al !
I agree with Niz. Check for air leaks, LEAN mixture or exhaust leaks especially near the flange where the exhaust bolts to the head. May need a new gasket.
BTW.... if you try to tighten those exhaust manifold nuts....BEWARE....they break off really easily.
The studs are really fragile and don't take much to snap em off.
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Post by albongo on Mar 23, 2015 16:48:40 GMT -5
Thanks for all the support guys.  I think I've found an exhaust leak!  Top bolt definitely looks like the culprit. Any ideas on the best fix?  |
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