50cc Big Bore Kit Help By 4treybrown (Read 236 times)

[4treybrown]

Hey all! Forum noob here. I have a 50cc 4-stroke GY6 (Chinese scooter) that I put a big bore kit on. The kit was advertised as 100cc but 80cc is more like it at best… Here is where I need some help. I installed the BBK, timing is correct, I can turn it with the spark plug out and it appears to be successful. I’ve done this twice on Genuine Buddy 2 strokes without a hitch. On this 50cc 4 stroke tho it seems, with the spark plug in, that the compression is really high and it has some difficulty starting. I can get it to start but it won’t idle. If I keep giving it gas, I can keep it running. I drove it a little and it won’t break 20 mph. Another thing, when I was driving it and let off the gas to stop at a stop sign, it was dragging bad. It was like I was driving a manual transmission car and was using the gears to slow down. The feeling was like I was going 40mph in a car then shifted in to 2nd gear if that makes sense. I took out the spark plug and tried starting it and it spun perfect. With the plug in tho, that’s when it appears to build so much compression that the starting difficulty begins.

I am at a loss on this one. Usually my compression issues are that it’s too low lol. Everything else on this thing is stock except when I did the BBK I also upgraded the cam to an A-9 cam. And ideas on what I can do to troubleshoot? One last thing to add, the BBK came from the “jungle” marketplace and the kit only included the jug, piston, rings, gaskets and G-clips. The rest is all stock. I am open to all troubleshooting suggestions. Thanks all!

[krankin]

CHECK THE VALUE ADJUSTMENT I BET THE EXHAUST IS TIGHT