My brother's 1985 YFM200 suddenly developed a hard starting problem. He has had the bike for almost a year and has put many, many trouble free miles on it except for it leaking oil around the head gasket just below the timing cover. About a month ago it suddenly began to start hard and occasionally stall while driving so I took the carburetor apart and cleaned it but it made no difference. You have to hold the throttle on a bit to get it to start and it will not start on the electric start, only on the pull start. The compression seemed to be a bit low when cranking it over compared to my Bayou (I couldn't find a compression tester to fit the plug hole so I don't have an exact number) so we decided that when we changed the head gasket to fix the leak we'd replace the rings, gaskets, etc. I got it all together last night and it's behaving exactly the same way and if I adjust the idle high enough for it to start without holding the throttle on a bit it idles way too high. I've only had it running for a few minutes to check for leaks so it's not broke in yet but it definitely has more compression now so I doubt it's a compression problem now. Any ideas what could be causing the hard starting?

 

Have you checked the valve clearances?

 

Yes check your valve lash.

 

I have the problem fixed but I'm not sure what fixed it. I went around it and tightened up the starter bolts and cylinder to base bolts that were loose and when I tried to start it it fired right up on the electric start and has been starting great ever since, even this morning when it's only 2*C out. Hopefully today we can finish breaking it in and get all the plastics back on it today.

 

Thanks to everyone for answering my questions. He's put quite a few miles on the bike since I got it back together and it has much more power now than when he bought it a year ago. No more burning/ leaking oil either.

 

The cylinder to base bolts being loose could have caused the engine to suck air and lean the fuel mixture, which caused the hard starting and stalling. Glad you figured it out.

 

What are the valve clearances for the yfm200dx(a)?

Sorry for the thread hijack