1988 YZ 125 problems

[schurchill39]

I just bought a 1988 yamaha 125 YZ from my neighbour. It was sitting for a yearish so when I bought it I did a little bit of a tune up (just sprayed the carb with some carb cleaner etc and changed the gear oil and the fuel), then it started up and drove fine. I have only taken it out once since I got it started for a little more then an hour total of riding. In this time I fouled the plug, and replaced it with a new one, drove it for 10 more minutes then packed it up.

The other day I took it out for a quick boot down some back roads and I was in third WOT (EDIT: By WOT I mean I had JUST shifted to 3rd and had it pinned for all of 5 seconds max then...), when the bike just suddenly stopped! It stopped fireing, the back wheel locked up momentarily (because I was on a loose gravel road), it was almost like I ran out of gas eventhough I had half a tank left. I tried for 20 minutes to kick it over and it wouldn't.

So I push it back home and check the plug out... its fine. I check for spark, I have some, I can smell the fuel -plus it was just working- so I assume I have fuel...

I figured the carb got clogged up because I didnt rip it apart when I first got it to clean it.

I just finished doing that, I scrubed it spotless and put it all back together and now it still wont fire.

I am stumped. I don't know a whole wack about bikes in the first place so I cant really do much more other then take it into a shop but I figured I would ask you guys first.

Any ideas what the hell might be going wrong?

EDIT: It has about 20hrs on a new top end I was told.

[MX86]

check your compression...

[schurchill39]

I dont think the motor is seized because when I try to push start it you can hear it try and run and if I take the spark plug out and cover the hole with my finger I can still feel that there is compression. There is no reserve tank (that i know of), and there is fuel running into the carb.

Edit: I'll see if I can get my hands on a compression gauge. What should it be sitting at?

Lets say the compression checks out and its fine, what is the next thing to look for?

[MX86]

120 ish is min.

could be stator, reeds, or some other things i'd have to do a little diggin to see how this thing is wired

[schurchill39]

I did a compression test and it was only reading 30psi....

So i riped it apart and sure as shit the piston is scored and the ring is done. So I guess I have to go and get the cylinder bored and a new piston and ring.

Anything else I should grab while I am at it besides gaskets etc?

Thanks for the help, I really appreciate it!

[MX86]

Piston and rings
Bore cylinder
Gaskets
radiator fluid
new tranny oil
check clutches for wear
go through swingarm and re-pack bearings.

just some preventive matinence...

[BIGBLOCKXJ]

You got PM!!!

Mike
248-310-7902