79cc Lifan engine problems

[MinibikeMan]

My neighbor recently gave me a doodlebug db30, it has a 79cc Lifan flathead. The engine was really weak, so I milled the head to increase compression. The engine runs great when it's cold, but when it gets hot it refuses to run.

Does anyone have any idea what's going on?

Thanks

 

[DieselTech]

My neighbor recently gave me a doodlebug db30, it has a 79cc Lifan flathead. The engine was really weak, so I milled the head to increase compression. The engine runs great when it's cold, but when it gets hot it refuses to run.

Does anyone have any idea what's going on?

Thanks

What's it do when it's hot? Does it run, but just poorly? Does it die & then wont start? Give us a lil more info & will see if we can diagnose your problem.

 

[MinibikeMan]

When it gets hot it acts like the choke is on. It fires once or twice, and then it won't start till its cold.

 

[DieselTech]

When it gets hot it acts like the choke is on. It fires once or twice, and then it won't start till its cold.

Next time you have it running, spray carb cleaner or wd40, something to that nature around the carburetor & intake manifold mounting locations. Listen for a rpm change in engine & note where you sprayed to cause engine rpm change & that's a air leak at that area. Also, next time it dies, see if it's still got spark at the plug, I've seen where the plug gets hot & is bad & will loose spark. Also I've seen the ignition coil do this same thing. The only other thing I've seen is vapor lock in the fuel system, but that is rare.

 

[Chainlube]

My neighbor recently gave me a doodlebug db30, it has a 79cc Lifan flathead. The engine was really weak, so I milled the head to increase compression. The engine runs great when it's cold, but when it gets hot it refuses to run.

Does anyone have any idea what's going on?

Thanks

What is the valve lash set at? If it's a little tight, it won't run when it warms up.