Topic: A real ornery Yami

[country joe]

Once again, I have a post unrelated to a Honda sohc. Gee, surprised? Anyway as I still lie in wait for the ever f*&^ing elusive title for my Honda CB550, I've been messin with a 1979 Yamaha IT 400 dirt bike that has been in the family for a long time and sat stagnant. Well, her's what it she does, I can get her started with just a few swift kicks when the engine's cold. It runs okay. then after maybe 5 or 6 minutes when it starts to warm up good it dies out like it's out of gas, and the #$%* won't start again. I do not have the original carb on the bike number 1, the one on it is a flat slide Mikuni that is 38mm. I don't know if this has anything to do with my problem, but I'm sure it doesn't help. I don't understand why it runs for such short bursts like this. It doesn't idle either. I've played and played with the carb, but she won't idle! So, when I first got her started it ran enough to putt around my property, you just had to ride like an old flat tracker cause it won't idle. But now it won't stay running long enough to even ride. I am not that well versed in two strokes, but everybody says how simple they are. BULL$%#^! This thing is a pain in the a@#. I don't know what to do anymore. Years ago we rebuilt the top end and it has little to no time on it. I have never split the cases, which is my next recourse of action. I know two strokes have pressurized cases, could there be a leak some where in them? I don't know. Please help. Thanks.

[WFO]

sat stagnant = a total cleaning of the fuel system even more so with pre mix bikes iam guessing you have something clogging up the fuel supply after the warm up so first eliminate that as a problem then proceed and that means removing the carb and gas tank fuel filter and fully inspecting and cleaning it.

[BeSeeingYou]

I don't know much about the dirt bikes but the vintage is the same as my XS650 and I had similar problems that were caused by the vacuum petcock.  If you have the same one they often need to be rebuilt after they sit a long time.  It would not keep up with the flow and would run for a short time, die, and then after a bit when the carb filled up it would run again.

[8 Track]

When you're done cleaning the idle jet, you can always question the crank case seal.  I don't mean the seals per se, but the crank case halves.  Two strokes require a perfect crank case seal, or else they won't idle, they won't start to save their lives.  If the oil mix is too light, it won't run either.  They don't always sieze, sometimes they just stall out.  Again, it's that seal thing.  When my two strokes sit too long, it's always the primary jet's clogged.  Always.  Btw, step one- new spark plug.