My rm 125 is jumping out of gear?

You should feel a surge of power as the power band comes into rpm range. If not, the first thing to check is the exhaust. A plugged ( or partially plugged ), exhaust system can be the problem. If no mud has plugged the exhaust, then remove the exhaust system and go for a test ride down the street to see if the power band surge problem is fixed. This would indicate an internal collapse of the exhaust system. You will need a new exhaust if that is the case.

The following possibility for your problems are mention below kindly check
1. Check the Engine Acceleration 2. Clean the plug 3. Check for any blockage in silencer 4. Clean the carbonizer
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it may just be dirty carb jets or no fule from the tank getting to the carb if it runs better with the choke on its likly to be jets blocked up

cluch sync is out. Are you rpm shifting or using clutch always? Bent or burred gear slider

Either your gear selector adjustment needs to be re-set (right hand side of motor inside the clutch cover, there is a hook and claw mechinism that can be fine-tuned) or the gear selector drum stopper is badly worn and will need replacing (experts only, as this requires a total engine strip down).

either 80 or 90 weight gear oil should be fine. and it either has a sight glass or more likely a check bolt to fill it to. it should take less than 1 quart

sounds like it might be a chain too loose or worn out and it is jumping teeth on the sprockets

Scatter gun approach > thoughts to check out > > >
Clean and dry the air filter? Go back to a stock main jet, at least to check things out? Are "O" ring seals on the main jet going bad?Partial internal collapse in exhaust (remove exhaust pipe & do a quick run down the alley), Install a new stock NGK spark plug, Be sure battery connections are clean and tight, Be sure intake manifold and carb are good and tight.

Hope this helps!

Did you check the main crank drive gear i had a 96 rm 125 with that problem. Its a cheap fix if thats the case but the only problem is that the engine needs to removed and the case needs to be be split. If thats not the problem with the case split it should be ovious.