Hello, I have a 50cc Chinese quad with a ATD 90-A engine on it. I don't know the history on it, but it sat for a couple of years. The engine cranks with the starter motor just fine, the battery is new as well. I have checked for spark, I actually have it! I cleaned out the carburetor made sure it delivers fuel into the combustion chamber. The engine still won't run or pop, even on starter fluid. It may need a valve adjustment on it, which is .05mm, but I can't fit my feeler gauge into the tight spot. I was looking at the questionable Chinese electronics and stumbled apon this, which may be my problem. I don't know what it is, but it is connected to the control switch on the handle bar and is connected to the horn. It may be connected to other things, but that is what i could see visually without bringing my multimeter into this. There is a black wire that looks cut, it doesn't come out of where the rest of the wires are, instead it comes out on a different side. I have included pictures of this. Any help would be great!


ATD 90-A engine


Mystery electrical box

Cut black wire

 

If you have a spark and the engine turns over "on the button," whatever that black box is, it isn't hurting anything, so leave alone. I would guess at it being a disconnected remote kill switch. The valves need some clearance or compression will be lost, so feel for play with the engine at TDC on the compression stroke, no play = no clearance. If that is OK, check compression anyway, under 90psi and the top end is going to need work, though I had a Honda 70 with less than 30psi and it still ran (very badly). Check valve timing, and that the piston is on TDC when the mark on the flywheel says it is.

 

Thanks for the reply! When I get some free time, I will check the valves, I had a similar problem with a different Chinese quad and a valve adjustment solved it.