Baja Dirtrunner 70cc no start issue?

[Kazman]

New to the site, tried to search the issue without a right answer. So thanks in advance for any suggestions you all may have. Quick history of me. Father of two boys 13 and 10 years old. 13 has been riding for years, 10 year old just started to show interest but wanted us to build a fixer upper. I am an ex auto mechanic/service manager now in sales.

So I do know my way around engines. This is what we have. We bought this little bike knowing is didn't run and wasn't very well taken care of at all. We rebuilt the entire bike right down to every nut and bolt. New tank, seat and plastics, carb everything. The engine had spark and fuel but no compression. So we tore down the top end and went over everything. Had a stuck valve which is now free and works fine. timing is spot on yet it feels like there is no compression coming out of the plug whole, but there is a LOT of air coming out of the vent on the crank case.

Is this something somewhat common that someone has come across??

Thanks everyone!!!

 

[gottagetacheaperhobby]

Did you put new piston and rings in? Sounds like all the compression is leaking past the rings into the case.
These engines don't have much compression even in good nick, you can usually start em by pushing on the kicker by hand lol

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[motodevo]

Make sure it isn't just the clutch slipping. The kicker drives through the clutch so if its slipping (adjustment,worn out, dried out plates from storage with no oil, using an oil not designed for wet clutches)the top end will hardly move which could explain the lack of compression at the plug.

 

[Kazman]

Thanks for the ideas guys. It has fresh Royal Purple in it, I did not do the piston and rings as they seemed to seat well and still has very nice crosshatching in the cylinder head walls. When kicking it over everything turns over as it should I can see the valve moving. SO I guess my diagnoses on the piston and rings was wrong. Back to the bench with the engine.

 

[rotn50]

Sure ya got the gudgeon pin in???






That was a joke but after years working on these I have seen it lol.

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[rotn50]

[emoji109]

 

[rotn50]

Any updates?

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