so i was out at el mirage this weekend, havin a good time on my 2000 yamaha YZ 250 (which is a 2 stroke) and im in top gear throttle pinned and the bike starts to bog down and then then engine just quit (i was going about 55-60 mph), it didnt seize, the rear tire kept moving and i can kick it over, but it wont start and is very difficult to kick over. There is oil in the trans, its not burnt looking or smelling, the gas was mixed right, coolant is filled (its water cooled) i just have no idea what went wrong with it. Since i have little experience with 2 strokes i was hoping someone could give me a clue about what could be the problem. there arent any valves to be stuck on a 2 stroke right? i did take the exhaust pipe off, looked in there it looked ok, and it was easier to kick over once the pipe was off, and then difficult/impossible to kick once the pipe was back on, so idk whats up with that. if anybody has any ideas id appreciate it, i might just take it to a bike shop since i dont know anything about working on bikes

(i know its a ford forum but most of you guys are pretty mechanically inclined so i thought id give it a shot)
thanks guys

 

That's odd, it should give a little bit more back presure but I've never heard of it that bad. Did you try starting fluid?

 

I'll bet it did seize. Not much to go wrong on a 2 stroke if you have fuel, spark and compression.

Did you remove the exhaust pipe while it was still warm?

Even though the fuel was mixed properly it could have been running too lean and the heat caused the piston to start melting, so you were able to kick it over while the cylinder was warm but when it cooled off the cylinder contracted and it tightened up because of the galling on the cylinder wall.

Pull the head off and take a peek at the cylinder wall - that will tell the tale.

 

i didnt try starting fluid, i didnt have any. I took the pipe off when it had cooled. I guess "kicked over" was the wrong term, i could get the piston to move, i could never get the engine to catch again or even almost catch, so i guess i never could kick it over, but hot or cold it was hard to kick. and if its seized its trashed right? cant fix that cept with a new motor... unless you bore it out i suppose? why would it be running lean if everything were mixed properly?

 

You can get it bored and put a new piston and rings in it.

Yank that head off and see what's going on!

 

ha ok, ill get on that!. actually on second thought im going to most likely take it to a shop, i already have one bike in parts in my garage i dont think a second one will speed up the process any, so ill prolly take it to a shop unfortunetly

 

Aw, man! You're no fun at all. We want to see carnage, not receipts from a bike shop!!

C'mon - just a few bolts and you're in there.

 

I didn't see any mention of whether you checked to see if it had spark. You can pull the plug, attached the wire, ground the plug against the head and crank it. You should see the spark. Best done in the garage with dim light. Should crank real easy with the plug out.

 

Yes pull the head off you will see whats up..There easy to rebuild. two strokes need to be rebuilt more often than a four stroke.Just my experiance with them..Lew

 

ok ok ok, ill take it apart myself and take pictures! lol ok let me get some dirty clothes on and get crackin on this. and bill i hadnt yet chaecked for spark. Everything i did to it was out in the desert and i didnt want to risk opening everything up out there if there wasnt anything i could do about it. But i will do that as soon as i get it ripped open. thanks guys

 

ok spark is plug is out, id check the spark if i could kick it, but with all my weight, and im not a small person, on the kick starter, i cant get it to even budge, so looks like seized is a real possibility...

 

Well, that eliminates all the simple stuff. Unless you know you are up for it, suggest you take it to the shop. The last thing a shop wants to see is the bike come in in pieces because you took it apart and got stumped.

 

SEIZED

Bummer.

 

didnt you say that when you had the muffler off you could kick it over? if that got plugged up and wont let air out the piston wont move? you could have thrown a rod like i did... if you take the head off (1 or 2 piston?) and it turns over and the piston just moves out of the engine thats what happened.

 

I dont really like motorcycles or know to much about em, but on a 2 stroke outboard motor the the symptoms here sound like ingestion of a reed valve at high rpm causing seizure, as soon as it cools off enough it will move again........But the damage has been done, good news is 2 strokes are simple to overhaul. Take it from someone who has worked on 2 stroke outboard motors most of his life.