I have a YS 63FZ. The problem I'm having is it starts fine (cold, low compression), but when it get hot, it detonates, and then quits. I have reset the needles to factory settings, and it has a new diaphram. Pressure is good. After it quits, the compression is almost non-existant (never was what I thought is should be). I can here it going out the exhaust valve, yet the valve doesn't seem to be open at all. I did take the cyclinder off, and blew into the jug. No leaking. Here is the real mystery. After I re-assembled the engine, compression is good, and now all seems normal. I have not started it yet, but will soon. Ever heard of anything like this before? Oh yeah, it never has idle very well. I had to keep the RPM's up to keep it running.

Thanks

Bob

I think I may have found the problem. The front bearing is pretty tight causing the engine to overheat. Any suggestions on removing it without breaking the case? Cook it in the oven?

The front bearing will press out from the rear once the crank is removed. There is a oil seal back there behind the bearing that will be damaged when you remove the bearing so replace it also.

Some heat and wood dowel works to push to the bearing out from the rear.

Or you could send it to YS parts and service they will look it over and fix any problems...You may have more probelms thatn justa bearing. Besides they work cheap and get the work done properly.
Besides you already have buy the bearing and the oil seal it won't cost much extra to have them go through and do the work for you. Probably less than the parts costs...they can give you an estimate before they do the work if you request it. Richard and crew are really good at what they do.

Troy Newman
Team YS

Thanks Troy. Let me say this duh. The porblem was to much prop. Put a 13/4 apc on her and all is well. Truns 11k slightly rich.
thanks again.