I have a yfm 80 that will turn over but it is very hard to start. Once u get it started it will run all day till it cools off.... It has a new battery, cleaned out carb, cleaned air filter, new plug but with new plug it still looks like it doesnt have much spark coming off plug???? I dont know.... Once u get it started like I said it runs good and will continue to start until u let it sit for awhile then back hard to start.... Any ideas on what it maight be or for me to look at... Would low compression cause it to be hard to start and after warm it would heat cylinder up enough to keep starting???? just a thought... need help here and any ideas r greatly appreciatted....

 

I had one of these with the same problem. It was the intake valve was a little too tight. Open it up and turn it just a little looser and it should fire right up even cold. I lived with this problem for like 3 years before I learned how to fix it. I hope this helps...Jeffrey

 

Ditto.... adjust the valves. Makes a huge difference.

 

Just open up the valve on the carb side on top and loosen it just a little put it back together and try it. I think you will be happy!

 

when it warms up the valve is open good but as soon as it is cold it is not open at all. is why.