2003 RM125 cutting out

[MrkCottingham]

Working on a friends RM125 2003 model and the bike has ran great up until he mixed his fuel wrong (too rich). We drained the tank and carb and put fresh 40:1 mix in as usual and the bike cuts off at high rpm's in every gear like you just hit the kill for a moment, let off gas a second then it will pull again. I checked the compression and it is 120 which is in my mind a little low but will this cause the problem we are having? The jetting seems to be the path to follow but I'm thinking that nothing should have changed since it was running great before?? Any ideas to try?

Thanks,
Mark

 

[SirHilton17]

120 PSI A little low thats real low if you ask me...... i get upset when my 04 kx 125 falls below 175 psi .... Its got 204PSI now... but yes i do have to run race gas

 

[Agie rider 76]

A worn topend creates "rich" conditions.

 

[MrkCottingham]

plug is black, can the silencer packing cause this? The jetting has been correct in the past, I believe something has changed, the compression is 10# lower than 3 months ago. The bike has great power up until this happens at high rpms.

Thanks,Mark

 

[Chili]

If the jetting was fine it's unlikely the cause of your problems now. 120 is significantly low by my standards but each compression tester is different. I rebuilt my son's 80's in the past when they dropped below 130. First place I'd start is with a new plug and then work from there. I can't recall what our compression numbers where on my son's 03 RM125 when rebuilt but they were definately 175+. For sake of asking later what is the jetting specs in the bike now?

 

[MrkCottingham]

air filter leaking, torn at seal. Clogged the air screen to the air jet! Thanks guys.

Mark