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My rm125 05 ran very well for 20/30 min. then all of suddent engine died like if the spark plug was gone, kickstarter can't be moved by a Millimeter, My engine is seized, some people said it is badluck, other said it is because the bike was too lean (didn't need chocke to start it), some say "sand" but my air filter is alright

what might be to replace? cylinder? piston? crank? cranks bearing?

you can seize a 2 stroke pretty easy by overheating it actually .
when it cooled off can u kick it over ?
You might want to up the oil mix a little bit , when people told you it was lean they didn't mean your jetting they meant the oil mixture in your pre mix

nope, 30:1 like service manual, they told about jetting too lean because I could start and run the bike without the choke

Thats not too lean... My cousin runs 42:1. Does it have oil in it? What color is it?

Lean has more to do with the jetting then the mix.

Did you ever do a plug read?

2-strokes can be prone to heat seizure if you run them too hard before they are at operating temp. Once you tear it down you will know what happened.



Ride Red

Mhhh, strange, Because I started it without choke (that's why I think the jetting is too lean). let it ran 2-3 seconde on idle, then I twist the throttle a little bit, I did that a complete minute before going on the track. Was it the best way to warm it?

edit: also I can move the kickstart today, I didn't tried to make the bike start, just wanted to see if my crankshaft was OK. I don't care to put a new piston in (I already have a wiseco with rings and gasket kit) I don't want to have to change my cylinder and/or my crankshaft bearing (someone told me rm125 05 are prone to have loose crankshaft bearing)

If it starts without the choke and it is cold out, it isn't too lean. It's rich. A choke (Or enrichener) adds fuel during start up. If you can start with out that additional fuel, you aren't lean.

If you go gas assin' before the engine is fully warmed up, you can cold sieze the engine. If it is over rich, it will take longer to get up to temperature. You need to do plug chops and read your plugs whenever you change alltitude, temperature or oil type/mixture and or carb settings.

First of all I'm going to find someone near my city who rebuild 2 stroke dirt bike often, then I'm going to bring the part and my eyes to see how to do a top-end and how to adjust my jetting

but what happened is that it cold seized?
because It had time to warm up, 1, 1,5 minutes before going on the track and then 20-25 minutes riding hard on the track, it would have seized before

Sand was sucked into engine

air filter was not installed properly

goddamnit