01' rm125 low end bog?

Joined
Jul 29, 2005
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#1
Hi i have a 2001 rm125. When i give it wide open throttle at low rpms, it bogs down. It runs perfectly everywhere else. How can i fix this?
 
Joined
Jul 29, 2005
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#2
the bike has a pro circuit works pipe with stock silencer. There is also a lot of black sludge coming out of the silencer. its easier to start with the choke off, too. Please help
 
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Nov 12, 2004
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#3
First, its generally not good to go wide open at low rpm, the carb is sized such that it makes good power at high rpm wide open, at low rpm with wide open throttle the air velocity drops too low and the fuel doesn't atomize all that well. Try opening it a bit more slowly and notice at what point the bike is pulling best in releation to throttle opening (say at 2/3rds throttle) gradually feed in more throttle as rpm's pick up. Secondly, there isn't much reason to ride at low rpm's on a 125cc bike imho, use the clutch and trans and keep the motor singing.

If you feel that there is a problem (other than the operator:)) look into your carb jetting. A low rpm bog is usually from a lean condition at that rpm/throttle opening, but could also be from loading up. These will be two distincly different bogs. If its too lean, opening the throttle quickly will make it worse and there will be very little smoke. If its too rich and loading up it will be blubery, smoke a lot and eventually clean out and take off quickly.

If you determin that jetting isn't going to solve your problem make sure the powervalves are working properly, the reeds are sealing, the top end is in good shape etc.

good luck
 
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#5
lean out your air screw maybe? If it starts better without the choke that means it's too rich at idle speed.
 
Joined
Sep 22, 2019
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#6
What ended up fixing your low end bog I have the same scenario procircut pipe and everything? No wheelie power gurgles at low rpm no wheelie power? Thanks
 
Likes: The Redrider
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#7
How do you go wide open at low rpm? Interesting. Low end bog could be an air leak at the reed block, clean that unit and add new reeds, Boyseen of course! If that don't work, go one leaner on the pilot jet, and raise the needle clip one notch up fer lean. Clean and or replace air filter. Good luck , The Red Rider! 093009ys3.jpg
 
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#8
How do you go wide open at low rpm? Interesting. Low end bog could be an air leak at the reed block, clean that unit and add new reeds, Boyseen of course! If that don't work, go one leaner on the pilot jet, and raise the needle clip one notch up fer lean. Clean and or replace air filter. Good luck, The Red Rider! View attachment 20569
Hey! I think that I may have grenaded the top end of my 125 2 stroke while riding midrange in 3rd gear. How hard is this to fix and how expensive, what may I have done wrong to cause it to blow other than running to lean in midrange? It completely sputtered, bogged down, and stalled when it happened and won't crank. its a 2005 and I havent had it for long. ( i got it not long after I turned 13 and just turned 14 a few weeks ago)
 
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#9
Yikes! You might need a shop manual for this fix. First pull the spark plug out and squirt some pb blaster in there and see if the crank spins. If it does you might be in good shape. Make sure you machine is in neutral, put it up on a work stand or milk crate. Then do all the above procedures. next if it is indeed jammed, you will need to take the top end apart, with your shop manual at your side. If the piston is intact and no scratches on it and the cylinder, you should be ok. If its shattered and cracked, you are looking at big money. Hopefully its ok.....
 
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Sep 23, 2019
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#10
Ok thanks a ton, I already removed my seat gas tank and spark plug and I'm going to drain the coolant after school today, it seems like I am going to have to ship my boar off to get it replated which sucks but I have some parts for my top end already from a previously planned build so I'll see what I can make work.
 
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#13
sooo.... I got the top end removed and the boar is fine as well as the piston looks like its in perfect shape, so it looks like its the crankshaft, which really pisses me off cause there's an aftermarket hot rod shaft in it thats not that old so looks like im looking at a lot more work on the crank than I wanted to do.
 
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#14
sooo.... I got the top end removed and the boar is fine as well as the piston looks like its in perfect shape, so it looks like its the crankshaft, which really pisses me off cause there's an aftermarket hot rod shaft in it thats not that old so looks like im looking at a lot more work on the crank than I wanted to do.
Sometimes one can find a used crank shaft on ebay or at a cycle salvage yard, and I think they warentee them. Just check for slack in the connecting rod bearings, a little side to side is acceptable, but there should be on radial play. Try ebay, I found lots of goodies for my ancient CR's, you should be ok too, good luck!:$