QuestionThanks Mark I have obtained an other carb and put a full kit through it including needle jet checked the bowl level etc and it has made no difference. I have tried three different carbys now and the symptoms do not change, do you think there is a possiblilty of an electrical problem. Another thing I have noticed is that it runs very hot' the only thing I can find in the manual about timing is the stator or timing coil could be malfunctioning.
Thank you Bruce
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Hi Mark I am hoping you can help me with an old 1989 Yamy XT250 It won't rev out sort of holds back 'labours' at mid revs if you know what I mean, it will rev out after that but under sufference and lacks power it also back fires occasionaly mainly on deaceleration. I have changed the carby and coil with good working ones and also removed the air filter incase of chocing with no change. I have checked the valve timming and adjusted the valves to specifications. It seams to me as if the ignition timing is out but according to my workshop manual it is non adjustable can you please help thank you Bruce.
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Hi Bruce,
I suspect the carburetor mid-range needs tuned to correct the air-fuel mixture. Shim (raise or lower) the jet needle, or change the jet needle & needle jet.
Reinstall the airbox with filter and keep it in place with a stock exhaust. Tune carbn with airbox installed.
When tuning carbs, make one change at a time to know what effects each tuning has on engine performance.
If you want carb tuning tech information files, reply with your email address as requested and explained in my instructions.
Respectfully,
Mark Shively
AnswerI doubt an electrical problem exists because the symptoms occur only in the mid-range. This indicates a carburetor tuning problem.
When the electronic ignition fails, it either works or it does not. If the ignition pick-up coil is defective, it will affect the entire range. A defective charging system will cause problems in all ranges.
You can try different carbs, but you'll learn more by tuning only one carb and by making only one change at a time. Carb tuning is a slow process that often requires removing the carb and changing jets numerous times beofre the air-fuel mixtures are correct.
Try restricting air intake in various incriments with throttle position in the mid-range. Does the engine performance improve? If yes, then the mid range needs to be tuned richer. If not, lean the mid-range.
Learn to read the appearance of the spark plugs. Visit NGK's website for more: www.ngk.com/sparkplug411.asp
Visit Electro Sport's website and follow their electrical "Fault Finding Chart":
www.electrosport.com/electrosport_fault_finding.html
Respectfully,
Mark Shively
