I know this site is for scooters, however, I bought a chinese snowmobile for my son that I believe has the 150cc GY6 motor in it. I have a few questions that I believe could be answered here.

To start:
I bought this sled used from a guy who said it ran good but the battery was dead, I know, never take someone for their word. After getting it home and unable to get it to run properly, I turned to the forums to diagnose. Turns out mine, like most, didn't have the vacum lines hooked up to the fuel pump. Once I T'd the line and hooked that up, the machine fired right up and ran great. Which leads me to believe, that the machine has had 0 miles put on it since it coundn't have ran for the guy I bought it from without the line hooked up.

Heres my issue:
I have to assume the guy I bought it from tried lots of things to get it running, but couldn't, and obviously I have no idea what that all was. When I got it, the muffler was not hooked up, nuts were missing. I didn't realize that at first, I just thought the machine was loud, it runs good without it. When I hooked up the muffler, the motor will start but will not run long before stalling. We had a mild winter last year, so I ran it without. I know, not good!!! My question is obvious, why won't it run with muffler installed. Possibly the last guy tried different jets maybe? Muffler wrong size? I have cleaned the carb, I think I set the valves correctly. They were both closed, i set both intake and exhaust to .004. I assume it was to be a pressure issue, maybe muffler is to small?

Any help would be very much appreciated
thanks in advance
mark

 

What does exhaust flow feel like when it's running? If it has weak pressure maybe as simple as a stopped up or restricted exhaust.

 

I took off the exhaust and put the air hose to it, it seems to flow fine. It didn't seem like a big pipe though.

 

Do you think a maladjusted exhaust valve could cause this? I had never adjusted a valve before. I did some reading and it was pretty straight forward I think. Im pretty sure I got it right.

mark

 

Easy to adjust valves without worrying about "strokes" Just have the spark plug out,turn the flywheel and watch the intake valve only. As the intake rocker arm goes down and starts to come back up,look for either the marks on the cam sprocket to align with the head or the mark on the flywheel for tdc.Then both cam lobe should be pointing down or away from the rocker arm pads and you can check/adjust valve clearance.

 

So finally got to take another look at this. I coudn't actually get it to run for long, but I could deffinately feel exhaust, just not sure how much I should feel. I will take exhaust off again tomorrow and see if I can shove something down to see if there is anything plugging it
mark

 

I put a new carb on, and it fires up and runs good till mid to full. Idles all day and low speed seems alright. The main wasn't labeled, but I've tried a 108, 110, and 105. Moved clip up and down. I'm stumped. Would these have a govorner on them that could have gone bad. It doesn't stall out, it just Boggs and won't rev up. I pulled fuel line and it's flowing while I turn over engine, seems good, I did put on a new petcock. Any ideas would be greatly appreciated
mark

 

If it runs best with the 110 and still bogs might have to jump up to larger main than that and see if that solves it.

 

Do you think that would explain the muffler issue? How much of a jump would you recommend?

 

You posted that the muffler was clear and open. No harm in having a couple sizes over what you have in it now. If it doesn't help,then you possibly have other problems. And yes running without a muffler isn't the best thing to do as it can cause exhaust valve problems. If it cranks and run good at idle to mid throttle,jetting would still be my first thought,making sure fuel supply is good to the carb would be next.