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03 Rm 125 Jetting

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First time posting here


Have had my 03 rm 125 for over a year now and have still not been satisfied with how I've been able to get it to run. Here's some history it doesn't go back very far as the guy i bought it from was completely clueless other then the fact that he bought it from a friend of his that races mostly super cross, but since i got it. Last winter I was going to do a full rebuild but after finding that it had a brand new hot rods crank put in it i opted not to, but i went ahead and bored it out and sleeved it back to stock bore with a wiesco piston and rings because looked to have eat a ring or two.  It has quite a bit of port work on the intake side, but mostly dune style porting. After having it sleeved sands Motorsports worked the ports in the sleeve to match the port work. After going though the whole bike which took me most of the winter got the motor put back in this spring. Since then I've had nothing but problems with getting it to run properly. I have about 8 hrs. on the new rebuild and checked compression and it still good at about 150.


SO I narrowed it down to the carb


Here's my specs

36mm mikuni

main- before it was rebuilt it was drilled out really big after it was rebuilt i put in a 440

pilot- Before it was rebuilt it had a high 50 after it was rebuilt i put in a 40

My Float Needle and seat are 3.8

needle = 6bgy27-77-2nd position

needle jet- cant find a number

slide- 5.0

Float- b10

Float height is set lower to about 7mm because they are running a big float needle and seat so it wouldn't even open up at 8.7mm


I have vforce reeds

New air filter

Running a NGK br8eg

Repacked pipe


Power value spring is set a bit light compared to my other bikes



Stock Specs

main- 460

needle- 6chy17-62-4th position

pilot- 42.5

Float height 8.7mm

Float needle and seat 3.3mm


I'm guessing they had to put in a bigger needle and seat from a honda cr 125 because thats the only bike that i can find that i can get a 3.8 float needle and seat,( to run the drilled out jets that the guy before me had in)

Put in a new float needle and seat 3.8 like the one before

needle is bigger in outer diameter and taper so it will help it run leaner compared to stock

So all jets and needles are smaller then stock along with that i have port work and it is still way fat

(i know that my float height will make it richer because i'm running the float higher)


It runs with no power band at all (like a 4 stroke) checked and the power value is working

smokes and sputters like its still extremely rich i have fouled a lot of plugs

lots tar or sponge from the front of motor and also out of silencer

I find my self as a very aggressive rider so it not that i'm babying it


I don't know if i should go smaller with the jets?????  Or if i'm overlooking something else???


Tried to give you as much info as possible




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