here goes- its a 1987 yfm 100 moto-4.
was running good & now it wont start.plug and spark are good,air filter clean, float is working(gas gets to the bowl -level is good). dissassembled the carb 3 times and cleaned all the jets and passages, took the tank off and cleaned ,took the petcock and filters off and cleaned,it has an inline gas filter.
it started hesitantly after i cleaned the carb each time, then ran great through all of the throttle ranges. heres were it sucks- after sitting for an hour or so it wont start again . what am i missing???
thanks in advance

 

how warm is it down there. some of them older engines were prone to vaporlocking. Try running higher octane gas (92 octane) and see if that relieves your problem.

 

That is rough. I had a Kaw Tecate that would eat the stators. It would spark and run intermittently but that was it. Check the magnets in the flywheel. They may have become dislodged, giving an erratic spark. If the carb is dialed in and you have good gas, then it has to be the spark. Good luck

 

Consider this theory: The float valve inlet needle is not seating properly and is allowing fuel to fill the engine via gravity feed during the time that the quad sits idle. Cure= replace inlet needle/seat or shut of fuel line during down time. If this is indeed the cause, the engine may be running rich and fuel mileage would be down.

 

valve sucking into the head!

 

some more info--when set idle(not running) it appears that there is NO gas reaching the cyl. plug is dry.
once i worked the throttle back and forth 30-40 times and it started. how could this be? it runs perfect once it is started, but wont restart after sitting.

 

tHOR...you know what? I think I love you!!!
That's exactly what's happening to my sled. It runs fine, but it impossible to start unless we shut the gas line, take off the plugs and crank once or twice, then it runs great.
I think you found out my problem...you saved my tomorrow ride. Be proud of your knowledge!!!

 

these are all good answers but not the one i need...
DSEATER-i dont know what a valve sucking into a head is
yesterday i went out to start it and it fired right up -then two hours later it wouldent start again.
i dont believe its vaporlock because the float bowl is full and removing the tank cap dosnt change a thing .the float needle is seating ok. i checked the level with a hose attached to the drain line.
any one got any more ideas????

 

these are all good answers but not the one i need...
DSEATER-i dont know what a valve sucking into a head is
yesterday i went out to start it and it fired right up -then two hours later it wouldent start again.
i dont believe its vaporlock because the float bowl is full and removing the tank cap dosnt change a thing .the float needle is seating ok. i checked the level with a hose attached to the drain line.
any one got any more ideas????

01'warrior
00'mohave
97'lakota
97'XR80---STOLEN
95'bayou 300--STOLEN-recovered
87'yfm100 moto-4(two)
86'trx125
97'harley flstc heritage softail classic


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When the machine doesn't start have you immedilatlely pulled the plug and checked for spark? If no spark i would ohm out the wiring looking for a intermitted broken wire. Did you check on what SteveNB1 suggested? This must be driving you crazy, alot of work and no fix. Good luck.