35 mm carb problems on 98 220 kdx

Joined
Jun 26, 2007
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#1
I have both a 1997 200kdx for my son(18 new rider) and a 1998 220kdx for myself (20yrs motocross). My son is set on driving only the 200 so don't suggest the 220 for my son because that is where I started. The 200 was hopped up to be a motocross bike : fmf rev pipe & flow through silencer, boysen reeds,and a few mods to the suspension to make it very stiff. I wanted to slow the bike down plus bring the sound level down/ spark arrester because we have 96db max in BC forests Canada . I installed a stealthy fly wheel weight and modified the silencer to a two pipe (for noise and spark arresting) internal system that with new fibreglass packing. I wrapped the silencer inner wall with adhesive heat proof nylon tape( acts like a double wall silencer) and made a Kevlar lower pipe protector because the fmf pipe ringed a lot of noise. I switched the carbs from one bike to the other and with minor tuning at sea level the 200 (with 32mm) performs wonderfully with ability to idle slowly and get right on pipe immediately with a slower max rev because of the flywheel; and the trail riding ability is wonderful.
The problem I have is with the KDX 220 and getting it to run smoothly. The 220 runs on a stock carb runs fine with a stock flywheel. I had difficulty on the bottom end with the 35mm carb( from the 200). From mid range with the throttle to max RPM it has no power and the plug is black on a rev kill switch test. To make the mid range to run smoothly I had to move the needle all the way to the bottom(top notch on the needle) so it ran cleanly. At the low end all I could do was turn the air screw out to 3.0 turns to just run and stop the plug from loading up. It runs rough at the bottom and needs to clutched or hold revs up to keep the engine from loading up. I have a need to climb to much higher altitude but the needle is already at the bottom so I can not lean it out and the idle jet is still too big. I decrease the main jet 1 size then 2 sizes and I still have to put the air screw at 3 turns out. . I went to a smaller idle jet so I can get the bottom end to not load up I added a FMF torque pipe and Stealthy flywheel weight because I was impressed with weight on the 200 KDX.
I adjusted the float bowl to 16 mm. and no change What am I doing wrong? Is the FMF pipe limiting the revs or the should I be looking at changing the needle. Sorry for such a long letter but I wanted to try to give you the proper information. My home email address is pbanning@shaw.ca
 
Joined
Oct 29, 2005
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#3
I recently installed a used 35mm on my 04 KDX 220. It has the FMF Dessert pipe installed and the air box lid removed. I'm at sea level and have been very surprised at what I've had to go to for jetting to make it run decent. It ran terrible at first. I started high and have had to go all the way down to a #35 slow jet and the needle has been dropped to the top groove (needle all the way down). It currently has a #152 main jet and seems to have a good tan plug color after a high speed run. I'm afraid it may still be a little rich way down low but man what a difference.