I have a 150cc Chinese ATV with a Gy6 engine. I usually have issues with the carbuarator and I am good at cleaning them out. I have cleaned this one many times but cannot get the bike to run. It has strong spark but will not run by shooting starting fluid into the carb or into the spark plug hole. Good compression too. My local mechanic said he thinks it is a timing issue but does not know how to set the timing on a chinese atv since he has no specs on it. I have no idea of how to check or adjust the timing. Any help would be greatly appreciated.

 

Welcome to the forum Kenyaman66!

If you hadnt said its got good compression, Id say adjust the valves...With good compression, timing is about all thats left..The timing marks are on the flywheel...under the plastic fan shroud on the right side of the engine while sitting on the quad. If you turn the flywheel clockwise while looking at the side...there are 2 lines on the side of the flywheel...1 has a F and the other 1 has a T...spark should happen at the F...T is top dead center.

 

The timing is not adjustable (it doesn't hurt to check it though). The ignition timing is set by the pickup coil location near the flywheel, and the keyway in the flywheel (which sets the magnet position in the flywheel).

Are you sure you have good compression? Did you measure it?

 

Thanks for the feedback. Yes, I did measure the compression and it was over 90 psi so I am guessing the valves are ok. The guy I had work on the bike said maybe the timing chain jumped a link???? Seems impractical to me but I guess anything is possible. You say the timing is not adjustable but if it works in conjuntion with the flywheel, I am wondering if I sheared the keyway off somwhow and it changed the timing. I've had this happen on lawn mowers, but never an ATV or motorcycle. Any other ideas?

 

Shearing a keyway is possible...I havnt had that happen in a few years, ok decades. But it can happen....I would use the flywheel marks, pull the valve cover off and check the cam timing...

 

A new GY6 Engine will have around 125psi, we had one in the shop very similar to this case & it had 85psi & would not run & we assumed that would be enough, we took the top end off & found a small crack by the rigs on the piston... I mean HAIRLINE... way small.... we changed out the piston & we were at 130psi & it started right up.... maybe you have other issues with compression... just a guess??

 

It may also be the gasket drawing air on your intake manifold...

 

I'm hoping your reading this and I've gotten to you in time. I just did a rebuild today and timed my 150cc gy6 atv correctly it's the easiest thing. All you need to do is take your fan cover off you'll see the timing marks on the flywheel a T and F and a 1 with a line. Now you need to make sure your cam is top dead center to verify the correct timing mark. Take your top end cover off and look at the cam sprocket it will have 2 small hole they need to be flush with the head and a big hole facing towards you or straight out. Then go back to your flywheel and there is a metal lip look and see which timing mark you are set at. Mark the flywheel with a marker. This will ensure you are timed in on the fly wheel and the cam chain. Again I did this today and no problem. If you need more help pictures or abutting happy to help. Hopefully this is as far as you need to go in the top end. I had more issues getting my head to breat free.

 

Chevydad
I have the same problem, but I can't seem to follow your instructions on timing. Do you have pictures of this procedure?
Thanks
Geronimoejoe

 

Had hoped someone else would post as it must be 10 years since I rebuilt a GY6 top end and I can't remember much about it. Anyway, only way to check for a slipped flywheel is to check the piston is at TDC by looking down the plug hole, when the T mark on the flywheel says it is. As for valve timing, according to the post you quote, you rotate the engine to the T mark, then remove the rocker cover and the two holes in the cam sprocket should be level (half of each hole showing) with the top of the cylinder head. Why he rambles on about marking the flywheel, I don't know.