I'm having trouble with my Tri-Z 250 (typical 2 stroke engine, same as YZ250). I may have multiple problems going on, but it started when I first crank it up for the day, it's very hard to start and when it does start up, it blows what appears to be oil out of the exhaust, and it bogs for a few seconds, then will clear out, run fine, and start on the 1st kick for the rest of the day and doesn't blow any more oil out. It used to start up on the 2nd kick when the engine was cold. The reeds are good and I haven't changed the jetting/pipe/filter.

I just rebuilt the topend, bored it .040 over, shaved the head .030, and had it ported. It was running at 180 psi compression. I was hoping the rebuild would fix the problem of it being hard to start due to low compression, but it didn't help.

My other problem is, after the rebuild and after riding it around for a few hours with no problems, I took it to the dragstrip, and it was running great until it started blowing antifreeze out of the radiator overflow tube when the engine is revving high. What could be going on? I'm worried the crankcase seals need replacing, but what are the symptoms?

 

Anybody have ANY ideas?

 

usually bad crank seals cause the bike to idle weird if the seal is on the ignition side due to air leaking through and leaning the mixture and gear oil can get into the crankcase also which causes them to smoke more then usual...theres some trick to run ATF type F fluid in the tranny and if it has a ton of white smoke coming out then its the tranny side seal, but if you do that be sure to change the fluid to your normal fluid afterwards...a leakdown test would be the real way to check, but thats about all i can say to help.

 

OK thanks. How do I do a leakdown test?

 

Its usually done right after getting done rebuilding the engine or something since you gotta have the plastic, tank, carb, exhaust outta the way,

heres a good writeup on it that should work on any 2 stroke....

Pressure-testing a 2-stroke - ThumperTalk Community

 

OK thanks, I'll try it and see what happens.

 

Well, before I got around to the leakdown test, I replaced the head gasket hoping that was the culprit - it wasn't. During the test run for the head gasket the transmission broke a tooth off and locked the engine up. I tore the engine down and both crankcase seals did need replacing, but I don't see how that would have anything to do with the antifreeze problem. The antifreeze only circulates through the head, jug, and waterpump. Which brings me to believe it's still the seal around the head gasket or the water passageways are cracked. Anyone else ever have this problem or have any ideas?

I swear, if this thing keeps giving me trouble I'm going to part the stupid thing out on Ebay and go buy a 4 stroke!