2004 RM 125 won't start... Lost

[Joseph_Cox]

Just bought a 04 rm 125, rode it pretty much all day then towards the end of our ride I was going down a hill in 3rd gear kind of lugging and the bike died out of nowhere. I coasted to the bottom of the hill and tried to kick it over and it just wouldn't start. Got it back home and started looking deeper, got a new plug, new gas, and cleaned the carb out, still won't start, it's getting good spark and fuel. What else might it be???

[runnybunny]

Maybe check the kill switch and its wiring.

Edit: there's a spark so that's prob not it. Sorry I'm just dead tired right now .-.

Edited July 13, 2013 by runnybunny

[mx4god]

Air filter clean? Have you checked compression? You said you just bought it; may need a new top end.

[Joseph_Cox]

Ya if it gets spark when you kick it over that eliminates the kill switch or stator I believe... MX4GOD the filter is clean yes, haven't tested the compression with a tester but it does have some. I pulled the head off last night and might have found the problem.. The piston has a bunch of divots/pits in the top of it as well as the cylinder head cover.. Idk if I can post pictures on here or not, just joined yesterday..

[Kpoulz328]

Your bike sounds like it is eating your bottom end bearings. Eric gorr has a great article about two stroke top ends and has pictures of all different used pistons and what happened to them. Just find a pic that is similar to your piston, then read the description of it.

http://www.eric-gorr.com/incl/pdfs/2%20stroke%20top%20end%20and%20performance.pdf

[Joseph_Cox]

Well this is a picture of the top of the piston.

[Joseph_Cox]

.

[JBFL]

Something has come apart, pull the cylinder and check the wrist pin bearing 1st then look for blueing down around the big end of the rod. One of those little pieces caught the ring and pinched it causing big loss of compression.

[Joseph_Cox]

So best case scenario the rings are bad and it needs a new top end kit.... Ill pull the cylinder off and upload more pictures of the piston. The cylinder wall is clean and has no big scars or scratched that's the reason why I didn't think rings... Idk gonna tear it down and keep y'all posted. Thanks for all the feed back.

[runnybunny]

If its compression/piston/rings issue it should at least make a puff or putt sound when you kick it lots with full throttle.

[Joseph_Cox]

It does do that with full throttle @runnybunny... Does anyone have input on the piston condition??

[runnybunny]

Sounds like no compression to me. It's probably easier than normal to kick as well. I'd take off the cylinder as well, I bet you find big scratches or maybe you're just lucky and you need new piston rings.

The puff you hear is the ignition that's supposed to be pushing the piston down but it's instead finding a way around it.

Edited July 13, 2013 by runnybunny

[Joseph_Cox]

@runnybunny yes my kx125 has a noticeable increase in compression compared to the RM... I can kick it with my hand fairly easy... And I can see the cylinder for the most part when the piston goes all the way down and the walls are pretty clean not scarred or scratched...

[runnybunny]

I believe it's pretty narrowed down then. It's either leaking around the cylinder, the head gasket, or possibly the spark plug but I never heard of that. If the piston, rings, and cylinder look good then pop in a new gasket and see if she runs! That's about the best case scenario if you ask me ?

[Greta Fauchi]

FIND OUT WHAT WAS CAUSING THE DAMAGE ON THE PISTON AND HEAD! If you put a top end without finding out what chewed up the one you have now, you will be sad and out more money.

Edited July 14, 2013 by Jethrobolas

[Joseph_Cox]

Yes, hopefully I find a piece of broken ring or bearing from the top end...

[Joseph_Cox]

I have an update. Tore the cylinder off and found a couple problems first when I pulled the head off I heard a rattle like something was inside of it... Turns out one of the hex bolts inside the power valve housing wasn't even on it was in the bottom of the housing just hangin out... The piston ring was seized to the piston. And it had some pieces broken off of it. I didn't see any type of metal piecs when I took the head off. I was looking, but I'm thinking the went ONE of TWO places, out the exhaust port, or into the bottom end... Which brings me to more questions..... What should I do next? Obviously order the new parts for the top end. But as far as the chipped off pieces to the piston? Any input???

[Joseph_Cox]

[Joseph_Cox]

No?

[runnybunny]

You can either clean out the bottom end with a hose/gas/solvent and hope you get all the debris out or you can split the cases and be sure you got it all out.

Check for up/down play in the connecting rod. If there is ANY you'll need a new bearing down there and you'll be splitting the cases anyway. A little side-side play is ok though.

You'll obviously need a new top end kit, new or replated cylinder, and a new or refurbished head.

Be sure to rinse out your exhaust too just in case some bits ended up there. You don't want to rebuild the whole thing and wreck it all on the same bit of metal.

Edited July 29, 2013 by runnybunny