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Hello everyone,
I need a bit of help/advice with my son's 2001 RM 125....

It has a terrible bog on take off (I can't even spin the rear tire on take off while sitting in the mud)

a little info on the bike....
Has 173 PSI compression on the top end (cold WOT)
spark plug holds a nice cardboard color...
clean air filter...
fresh gas 32:1 (amsoil dominator)
new clutch...
bike never looses trans fluid...
has no air leaks that I can see or find....
reeds are in great shape and seal nice and tight.....
bike is stock besides the carbon fiber reeds and the new clutch....
running the stock jetting....

on take off I get the dreaded "baaawwwwaaahhh" but once past 1/8th throttle it clears up and runs like a bat out of hell....(again, I can't spin the rear tire in the mud on take off)

The air/fuel mixture screw has zero effect on the idle/bike....
(I have cleaned the carb many times....soaked over night, blew out all passages with my air compressor)

I have tried one size smaller and one size bigger on the pilot jet with no improvement....

However, I have noticed if I run the bike with the choke half way on the "take off bog" appears to go away? (I do have to play with the throttle if I want it to sit and idle but with the choke half way on the bog does appear to be gone) wouldn't that mean lean on the pilot?

what are your thoughts?
 

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new here myself!

compression readings are not screaming at me but I don't have the specs you need to rule it out! sometimes your local library will have something useful. and its been a min. since my 2 stroke dirt days! here's what I would do
1. just to rule out comp. squirt a little clean motor oil in spark plug hole (not a lot no more than a tablespoon full) and check compression again and see if it raises it a lot if it does its a indicater that ring might be bad! also before test be sure to ground coil don't need no sparks! that being said;
2. I would go into carb again sounds like idle circuit maybe plugged, you said you soaked carb overnight (I think) if so, soaked in what? if it wasn't the dip cleaner (usually comes in a gal like paint can w/ a basket inside) your probably not getting it clean! Gas, spray carb and choke cleaner most often wont do it! the dip stuff is an acid so don't get on skin and rinse with clean gas or solvent before blowing out passages and wear eye protection (very caustic), and you have to totally disassemble carb and follow directions on cleaner you don't need to soak all parts( I would just soak carb body and bowl prob is usually in carb body) be sure to remove all jets main and idle and don't soak anything that can be cleaned with spray cleaner, needle and seat,float ect. the problem is usually 98% of time in passage in carb body!
3. vac. or air leaks check rubber carb boot for cracks and leaks!
p.s. if you don't have a manual I recommend you get one for carb job some setup measurments,diagrams ect. for us diy mechanics its a must really! good luck hope that helps!
 

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Curing "Baaawwwwaaahhh!"

Baaawwwwaaahhh! usually caused by insufficient fuel. DOes it have a loping idle? Idle jet clogged, esp if adjustment screw causes no change in rpm, etc. Rebuild carb.

The idle must be RICH enough to allow the engine to accelerate to where the main jet starts supplying fuel. There may be multiple tiny portholes into neck of carb where idle fuel is supplied.

You can spritz faux fuel (ether, brake cleaner) WHILE accelerating the motor into the neck of the carburetor and if the enrichment causes it to go like gangbusters, you've diagnosed insufficient fuel.

Other common cause of "baaawwwwaaahhh!" in string trimmers and 2 stroke garden stuff is a plugged muffler. Confirm or rule out by cracking (loosening) header or muffler flange; let it roar and go for a ride.
 
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