Engine Trouble Bike has compression and begins to turn over but conks as soon as i stop pedalling

[Spencer Ducharme]

Hi there. I'm extremely new to the motorized bike scene. My bike is behaving rather oddly and it doesnt seem to be an issue I can find documentation on. A few notes beforehand.

I've managed to get the bike to have compression when the handlebar clutch is released and the combustion chamber is working. Fuel flow from carb is excellent, spark plug is generating spark, and piston and its chamber are in healthy condition. I have used the startup procedure as per the manual. Engine is a 2 stroke 66cc. And the kit is a skyhawk-gt5a made by YuanDong gas engine factory in China. I believe the kit was originally distributed as a Grubee engine but as it is older information is hard to find.

Problem:
When I pedal up to about 15 mph and let the handlebar clutch go the engine whirs into motion very well and it runs excellent. Essentially the engine only is running so long as i am pedalling and isn't continuing to run after i stop pedalling. Shouldn't the engine run under its own weight after a few cycles? To clarify, the bike is about 6 years old and sat for 3 in a shed before i got it from its previous owner who said it ran when he put it away.

I'll try to inform on anything else i can!
Thanks!

 

[crassius]

you should do a compression test - does spark plug get wet? does muffler get warm?

my first guess is that you're not firing at all

 

[Spencer Ducharme]

Spark plug does get wet. Muffler does get warm.

 

[FurryOnTheInside]

My first three guesses:
Throttle cable not adjusted correctly.
Air filter dirty and blocked with oil and grime.
Muffler blocked by oily soot or nesting critters.

 

[Spencer Ducharme]

My first three guesses:
Throttle cable not adjusted correctly.
Air filter dirty and blocked with oil and grime.
Muffler blocked by oily soot or nesting critters.

Thanks! The air filter was checked but i didnt know the muffler being clogged was a potential hindrance! I'll try that!

 

[crassius]

just loosen it 1/8 inch or so and see - I've seen many that sat a long time that had a lot of leakage thru deteriorated case & base gaskets - I get back wheel in air to run it and spray water mist all around cases to track that

EDIT; BTW, does it smoke a whole lot? if so, old fuel may have evaporated out of cases leaving tar-like gunk inside

 

[Spencer Ducharme]

Minimal smoke. Doesnt smell bad when it creates smoke. Smells like fresh petroleum.

 

[crassius]

still lot it could be - rings stuck in piston, main bearings rusted - did you do a compression test?

 

[Spencer Ducharme]

still lot it could be - rings stuck in piston, main bearings rusted - did you do a compression test?

Just did one this morning. Motor reads 110 psi.

 

[crassius]

I once saw a slide in a carb upside down - would barely run. Have had several that sat long time and ran pretty weakly, but could still do 20mph or so (some cleared up over time, some did not). Those weak ones always reacted to water spray around case seams, but tightening all and soaking in oil didn't help as gaskets were too far gone.

Were it here, I'd lock clutch and pull plug and see if there seemed to be any drag when turning motor.