04 CR125R Jetting Help

[MAV400]

Hi, I recently Installed a FMF Fatty pipe with a Shorty Silencer on a CR125R 04. stock setting.
MJ-420
PJ-40
Needle-2nd clip position
AS-2 out.
Mixing-32:1
This the stock setting. This bike was already fouling plugs since day one.The dealership looked at it and said it was the gas . We tooked it for a spin and fouled 2 plugs, so I moved the clip on the needle to the 2nd position and that help to keep the plugs for a longer time. Now after with put the FMF pipe and Silencer the bike is way too rich. I went to FMF website and their Jetting Specs are:
MJ-400
PJ-40
Needle-3rd clip position
AS-1.5 out
Mixing 32:1
I already set the bike like that and started it up and gave it a little ride around the block, but have not ride in the trails yet.
I also bought a 410 Main jet, because the areas that we ride are sandy and sometimes muddy just in case I need to go up.I think the 400 might be a little to lean and but we want to stop it from fouling plugs.
Also we are at Sea Level and most of the times High Temps and Humidity. Now is cooler some days only.I just want to make sure we are going the right way and not damaged the bike. Any words of Wisdom would be helpful. One more ? is this normal on Dirtbikes that they have to be lean out when you put a pipe. From ATV experience more Exhaust, more air therefore bigger jetting for more fuel. Thanks for your Help. :ride:

 

[MXP1MP]

Yea I would lean it out maybe one or two at most on the pilot and the same for the main. The going to the 2nd clip helped I would go for the 1st if that helps and it still is fouling out then I would say it's time to go to the next leaner needle. Doesn't surprize me that the bike is rich CR 125's are pretty notorious for that.

 

[MAV400]

Thanks

 

[ellandoh]

i would put the main back to where it was 420, leave the needle where you put it then get a 37.5 pilot and mess with the air screw. you are most likely not fouling while on the main. does it sputter on WOT runs?? need to be cleaned out when ridden easy for short times??

 

[MAV400]

We gave it a good ride WOT in an open pit and it ran OK. Now that you mention at lower speed that is when I think is fouling the plug. It did right after I put the pipe and started it up. And when we tooked to park to ride it did the same thing after we warm it up and were ready to take off again. It ran OK WOT but the airscrew was out 2.5 turns.

 

[MAV400]

Thanks for your help. Anybody else I'm still listening.

 

[MXP1MP]

Try going down again on the pilot the next size is 37.5 from the 40, mikuni starts going by 2.5 under 40. by 5's 40 and above. Pay more attention to the throttle position the pilot only affects first 1/4 anything beyond that to 3/4 is all the needle you ride most of the time on the needle. It's trail n error it's still fouling plugs black that tells me too rich still. 2.5 turns out on the air screw is like the very max you want for an air screw adjustment. Try getting a few size small pilots the 37.5 the 35 and try those if it still fouls it's time to look at the needle. All too often people try to jet around the needle cause it's the most exspensive jetting piece but one of the most important.

 

[MAV400]

Thanks for your Input. Me and my brother are getting all the jets we need and planning on going some time next week during the week so we can ride and see where we end up. During the week less riders around and we can do the testing better.