91 rm125 fuel problems?! - Motorcycle-Journal Forums

ajm655 · 05-16-2006, 12:23 AM

so i just bought a 91 rm 125. It needed a top end so i got it for a steal ($500) Ive never seen the bike before, which sucks now that i cant get it running properly. I have a limited knowledge about two strokes, but more than enough skill to follow a service manual. So the bike initially starts and runs ok, but it will not idle. If i tip it over a little bit, fuel comes out of the overflow hose at the bottom of the float bowls on the carb... Floats are stuck? I opened up the carb and put it back together according to the service manual. everything seemed fine. So when i try to ride it, it will run pretty rough and eventually flood and die. the plug will be fouled and it wont start untill it is clean. Here are the things i have tried:

1/4 turn of the pilot air jet
throttle cable free play adjustment
throttle cable routing
cleaned air filter
replaced plug to the correct one ngk bregv i think
compression check ok
spark is large and bright blue
fuel is getting to the base of the carb (open peckock causes alot of gas flow)
mixture is 20:1 according to the manual

what else could it be? its got to be in the carb correct? Should i try leaning the pilot air jet more? Im not about to take it somewhere to get it fixed. Ive never done that in my life. HELP!!!!!!!

btw- it has an FMF gold pipe and power core silencer.

robcromwell · 05-16-2006, 01:02 PM

I had somewhat of the same problem with my bike. I tried everything to do with the carb. Adjusted the floats according to the manual specs, adjusted the air screw to the proper setting (1 and a half turns out) and cleaned the carb out as well. I still had the problem. The problem turned out to be a loose wire coming off of the coil to ground. One thing you should do is check all the wires and make sure none of them are grounding out or touching each other. Another problem could be a plugged exhaust system. My exhaust was plugged because the person who owned it first was running it too rich, and caused similar problems to what you described. Try these things and see what happens.

Dave2122 · 05-18-2006, 11:12 PM

There is a needle valve that attaches to the float assy. If it is worn out it will let fuel leak into the bowl even if the float height is adjusted correctly. You need to look at the rubber tip on the needle valve. If it is grooved or worn replace it. Also make sure the float height is correct. It doesnt take much to have the floats get out of wack. Incorrect float height is a common problem and a simple fix.

05-16-2006, 12:23 AM	#1 (permalink)
ajm655 Newbie Joined: May 2006 Posts: 1	91 rm125 fuel problems?! so i just bought a 91 rm 125. It needed a top end so i got it for a steal ($500) Ive never seen the bike before, which sucks now that i cant get it running properly. I have a limited knowledge about two strokes, but more than enough skill to follow a service manual. So the bike initially starts and runs ok, but it will not idle. If i tip it over a little bit, fuel comes out of the overflow hose at the bottom of the float bowls on the carb... Floats are stuck? I opened up the carb and put it back together according to the service manual. everything seemed fine. So when i try to ride it, it will run pretty rough and eventually flood and die. the plug will be fouled and it wont start untill it is clean. Here are the things i have tried: 1/4 turn of the pilot air jet throttle cable free play adjustment throttle cable routing cleaned air filter replaced plug to the correct one ngk bregv i think compression check ok spark is large and bright blue fuel is getting to the base of the carb (open peckock causes alot of gas flow) mixture is 20:1 according to the manual what else could it be? its got to be in the carb correct? Should i try leaning the pilot air jet more? Im not about to take it somewhere to get it fixed. Ive never done that in my life. HELP!!!!!!! btw- it has an FMF gold pipe and power core silencer.

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05-16-2006, 01:02 PM	#2 (permalink)
robcromwell Newbie Joined: Apr 2006 Bike: 1984 RM250 Location: Alberta Canada Posts: 11	I had somewhat of the same problem with my bike. I tried everything to do with the carb. Adjusted the floats according to the manual specs, adjusted the air screw to the proper setting (1 and a half turns out) and cleaned the carb out as well. I still had the problem. The problem turned out to be a loose wire coming off of the coil to ground. One thing you should do is check all the wires and make sure none of them are grounding out or touching each other. Another problem could be a plugged exhaust system. My exhaust was plugged because the person who owned it first was running it too rich, and caused similar problems to what you described. Try these things and see what happens.

05-18-2006, 11:12 PM	#3 (permalink)
Dave2122 Sprocket Pilot Joined: Sep 2004 Bike: Which one of the 9? Location: USA Posts: 887	There is a needle valve that attaches to the float assy. If it is worn out it will let fuel leak into the bowl even if the float height is adjusted correctly. You need to look at the rubber tip on the needle valve. If it is grooved or worn replace it. Also make sure the float height is correct. It doesnt take much to have the floats get out of wack. Incorrect float height is a common problem and a simple fix.

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