2strokes4life

Member
Apr 1, 2009
39
0
Here's the deal. I have a 2002 RM125. I bought it off of CL earlier in the year. It was a mess. It has a new top end including cylinder. Bottom end is solid. It has a new FMF Fatty pipe and new FMF silencer. I also replaced the stock air filter with a UNI. After the rebuild, I rode it slow and followed break in as I do with all of my bikes. I ride mostly 250's. This is my first 125. I'm not real sure about the low end power of a 125. I assumed they wouldn't have the torque a 250 does. I'm having a real problem with the low end off idle. I know what everyone is thinking. Jetting right? Listen to this. The bike idles perfectly. The mid to top end is amazing. The problem is right off idle. I even bought a JD jet kit thinking the jetting was the issue. I thought it was a lean bog. Now I don't know. I have tried everything. I have had the carb completely apart and cleaned and recleaned. It is spotless. I have sprayed carb cleaner and blown out all of the fuel paths. There is no junk stuck in the carb. When I take off it wants to bog. If I just start to take off and peg the throttle it just bogs and will die if I hold the throttle wide open. If I slowly give it throttle it will open up and scream. I can't figure out what is causing this bog. 1st thought was lean bog, 2nd thought was debris in the carb. Please help me my brothers and sisters. I'm almost to the point of buying a new carb. Could I switch my 2002 CR 250 carb to this bike to test it out? It has to be in the carb, but I don't know where.
 

Garrett T

Member
Oct 22, 2009
5
0
Could your floats be to high. causing more gas to go in so when you pull down the gas, to much goes in causing it to bog??
 

2strokes4life

Member
Apr 1, 2009
39
0
I'm pretty sure the reeds are good. I remember them being good when I replaced the top end, but I'll double check. Might be a good idea to go ahead and replace with boyesens anyway. Yes the float height is dead on. I actually ran this problem by a local Suzuki mechanic today. He said that the problem could be the part of the carb in the bottom where the needle seats. I have looked at the parts fiche and don't see any parts that come apart. It looks like it is not serviceable. I took the carb apart again twice today and didn't see anything that looked like I could replace or adjust in there.
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
8,129
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Merrillville,Indiana
The reeds need to be closed all the way, the float valve very well could be bad. Its a yearly replacement item that can seemingly last forever, sometimes, and not. Some have seats that come out also. You cleaned the carb thoroughly and are having an issue locating it? Cleaning the carb means removing the brass and clean all the orifices and passage ways. That pilot passage, and back of the pilot can build up a lot of gunk, and you can't see it well. The gallon can with a parts tray carb cleaner works very well. Is the silencer packing fresh? Vintage Bob
 

2strokes4life

Member
Apr 1, 2009
39
0
I removed all of the brass. I looked through and blew carb cleaner through the carb passages. The brass is all new. JD supplies all of the brass with his jet kit. I took out the needle valve, needle valve seat, and the floats. I didn't see a bit of crud in the carb anywhere. I will check the reeds. The reeds are one thing I'm not sure about at this point. I didn't think the reeds would cause this bog though. The silencer and pipe are brand new. If the float valve was bad wouldn't it leak fuel onto the ground? I never have fuel spillage unless I lay the bike on it's side. The part I couldn't see was inside the needle jet. I took out the main jet and the needle jet holder, but I couldn't figure out how to remove the needle jet. This could be the issue also I suppose. I don't know how to remove it though. It doesn't look like it comes out. Air did flow through the carb body when I blew it from the float bowl side.
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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Merrillville,Indiana
The brass that the main screws into? I do not believe it comes out of that carb, when it does, it comes out through the top. The float valve does not necessarily have to puke fuel on the ground to be bad. A lot of times, it goes into the engine, causes weird jetting problems, it can seemingly LOOK fine. Replace the valve and seat. Vintage Bob
 

slinger34

Member
May 1, 2006
37
0
Have you tried adjusting the idle mixture screw. This will help air/fuel ratio at idle or jsut above. If it runs great other wise this could be your problem. See how many turns it is out.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
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Merrillville,Indiana
slinger34 said:
Have you tried adjusting the idle mixture screw. This will help air/fuel ratio at idle or jsut above. If it runs great other wise this could be your problem. See how many turns it is out.
Like it has an adjustable choke/idle? Where is the idle mixture screw at? Most are slide stops. http://www.bikebandit.com/suzuki-motorcycle-rm125k2-2002/o/m6558 . I do not like these guys prices though, Service Honda's are a lot better. Vintage Bob
 

2strokes4life

Member
Apr 1, 2009
39
0
I bought new Boyesen reeds and will buy the new float valve. I appreciate all of the help. I'll probably replace the reed valve gasket while I'm at it. I just replaced it when I did the top end, but since I'm opening it up, I'll replace it again. I'll report back. I'll let you all know if these components fix the problem. A lot of people on here never give feedback on what fixed the problem. I like to be able to read the old posts and see what the problems were. It makes me a better shade tree mechanic. Last night I did notice one thing while I was looking at the parts diagram of the carb. I was trying to figure out how to get the needle jet out and noticed that mine is missing part # 25. It is called a holder. What does it do? Could that be causing the bog. Maybe that limits the flow of gas going into the jets. Just a guess.
 

slinger34

Member
May 1, 2006
37
0
whenfoxforks-ruled said:
Like it has an adjustable choke/idle? Where is the idle mixture screw at? Most are slide stops. http://www.bikebandit.com/suzuki-motorcycle-rm125k2-2002/o/m6558 . I do not like these guys prices though, Service Honda's are a lot better. Vintage Bob

In the parts diagram for my Kx125 it list's it as a screw pilot-air. basically a needle valve that limits air throught the idle circuit. It kind of sticks out from the carb. Easy access. It is nothing like a choke. It will effect idle qaulity a little. But it is used to correct the air fuel mixture at idle. So if the problem is a lean bog then richening the idle mixture will give the extra fuel needed when hammering the throttle. Common setting for bikes are around 2 turns out.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
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Merrillville,Indiana
The air mixture screw. You use it to find where it idles at its highest, then count the turns out it is at. This will tell you if the pilot jet is correct, or which way for you to go. Vintage Bob
 
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