1980's?? yz 400

[trx400exat05]

well hey everyone i was riding with my friend today and he has a yz400 its 2 stroke and we were coming back to my house and he was at the end of his 5th gear reaching 6 and his rear brake locked up and started boggin out and shut down...... when we tried to start it again and he aid he felt like the compression on the kickstart was less and it backfires when he kicked it! we think it blew up but were not sure.... he checked his spark plug(S)( two for if one fouls out) and the looked white which means he was running lean soo im thinking he did sumthin like blowing it up but my dad came home and tried to start and he said it sounds like a timing chain problem .... soo i was wondering what u guys think is wrong.... thanks

[banshee93]

well if its a 2 stroke like you said then there is no timing chain so that cant be the problem

[smr]

sounds like the crank.

[Tom TRX250R]

It sounds like he was running lean and needs a new top end. Do a compression test and see what your compression is at... That will tell you alot, and if it is in fact low compression then take off the top end and check for scores on the cylinder wall.

[trx400exat05]

well today he told me that the piston rings were messed up or sumthin but i also he had low compression, he could feel it in his kickstart and when he took out his spark plug he could feel it... yes he was running lean on both spark plugs .. ill let him know to check his topend