Chinese 50cc No Start

[jbreeves3]

Hi,
I got a 4 stroke 50cc dirt bike in an auction and cannot get it to start. I replaced all electronics, have spark, have 90-100 compression, and new plug smells of fuel so getting gas, no oil on plug. I removed air filter to make sure it could breathe. The only thing I can think of is there is no pipe on it for back pressure. Would this keep it from starting? Oil is good and clean. When I turn it over the chain and rear wheel move a bit so gears and trannie are not locked.
Thanks,
JB

 

[jbreeves3]

Wide open throttle compression check gets about 130.

 

[jbreeves3]

Adjusted the idle screw on the carb and it starts but will not stay running. Back pressure?

 

[my67xr]

Welcome to Minirider's.

Make sure you drop in here and say hello, Introduce Yourself thread

I would be removing the carby and taking the fuel bowl off and remove the pilot jet, the one that's toward's the intake manifold side of the carby
Check that the hole through the centre is open and not gummed up, and also check if the small hole's across the jet are open too.
Before you refit the jet look in at the bottom of the thread's where the jet screw's into, you should be able to see light through the tiny hole at the bottom where it let's fuel into the carby's bore.
This jet control's fuel to let the bike start and idle.

It might not start without an oil air filter on it too, it make's the air/fuel mixture lean
Also check where the idle mixture screw is set at, it should be somewhere between 1.75 and 2 full turn's out.

It'll still start and run without the exhaust on, but don't run it for a long time like it


Cheer's, Craig

 

[brraapp90]

Kinda a old thread but 4 strokes need back pressure but not as much as 2 strokes do thats why 2 strokes have the expansion chambers on the exhaust so im highly doubting it has to do with the exhaust pull carb and clean the hell outta it make sure carb is dialed in than new gas also make sure all ur electronics are plugged in such as ur cdi box good luck

 

[motoanth]

Have you check med the valve gaps!
I was having the same problem and found my I had no gap at all on the inlet made the adjustments it fired up on the 2nd kick


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