1981 250R Rebuild. Advice freely accepted

[Gripit'n'ripit]

Melted the piston on my 81 250r air cooled. Looks like the fuel leaned out, but mix was about 30/1. I've been told this can happen when too rich, if there isn't enough fuel to properly mix and dissolve the oil to carry it throughout the engine. There any truth to this?

Crank seals are good, was not smoking bad when it quit. On the bright side, spanked a 06 raptor 700 off the line. Kid looked like he was about cry. Anyway, the second time is when it broke.


Any advice for rebuilding or possibly building it up? I'd prefer reliability over performance. At the moment the motors been bored another 1.5 mil over. I'll post pics of the entire project later on. Thanks guys.

[MTS]

Got any more pictures of the piston..The other side's, Crown ect..?

[Yamaha_Rules69]

It dosent matter how much oil you mixed with the gas, you could have mixed it 10:1 and it would have still done the same thing. It looks like it got REALLY HOT, because of an air leak, or incorrect jetting, those will kill a 2 stroke. Make sure if you rebuild it, you replace all the gaskets, and try to determine if it still has an air leak somewhere. Plug chops will also help with the jetting story. If it were a crank seal, it would have been the left one, behind the flywheel, otherwise a bad gasket somewhere in the top end. Sorry for your loss, and hope you get it figured out!

[Gripit'n'ripit]

No apparent air leaks i can find. The chamber with the flywheel is clean. Still got a complete gasket kit and several replacement sets of bearings. Piston damage is mostly on the exhaust side. Damage to the sleeve was minor, but enough to warrant a bore job. As for the intake, i haven't rebuilt the carb yet, but at a glance everything appears fine. Reeds are original, they work, but don't seal down perfect. I'll tell ya more when i get the rebuild kit.

Off topic, improvements to performance i can make without sacrificing reliability. I'm planning on going from NY to OK to ride at Little Sahara and i do NOT want this to die.
Thanks for the feed back.

[D-dub]

Did you run an open air box with out rejetting? Could be a jetting prob related to the cold weather.

[MTS]

Just My opinion...looks like it Detonated itself to death....and Run hard..with bad fuel....

[Gripit'n'ripit]

Did you run an open air box with out rejetting? Could be a jetting prob related to the cold weather.

Did not rejet, aftermarket air box on before i bought it. It wasn't running perfect, but okay. I have no idea about the weather, happened 9 months ago (I procrastinate)

Just My opinion...looks like it Detonated itself to death....and Run hard..with bad fuel....

New fuel and oil. Mixed with AMS oil, is this preferred or should i be using something else? Yes, it was run hard. I was just about screaming the engine out when it died. Not the best decision.

Still going over the bottom for possible air leaks.
Keep the comments coming.

[Gripit'n'ripit]

Culprit found. I'm such a jack that i never looked much beyond the engine. 2 cracks/ holes in the carb boot adjoining to the engine. Now all i need to have a ride able machine in a new boot for a 27-28mm carb. Anyone have one for sale?

[Rollingmenace]

ill have to check if i have a boot i just sold one two weeks ago to another guy on this site.... As far as performance for your 250r theres company flowtek that does porting for the air cooled bikes and from what ive heard is about the best around for getting performance out of these machines... also check out this site alot of good info there http://air foolers.com