More RPM out of KDX 220 ???

[svttodd]

My buddy has a very nice 2004 KDX220. He had made it into a KX style agressive woods bike. It has a FMF Gnarly pipe and silencer, Boyesen reeds (the kind that are supposed to give mid range, with the stock reed limiters removed), KX style number plate, upgraded suspension, etc. Anyway, his bike is very powerful and fast, but he wants to be able to rev out each gear more. Here in Florida, first gear is unusable for him on sandy trails, and each gear winds out way too fast. What can he do to make the bike rev out a little further, and to get some upper rpm power? Will simple gearing change this, or is it just the nature of this bike/engine. His bike has great power down low, but dies off quickly up high. I have a nice 2003 KX250 that I use as a trail bike, and I seem to have the opposite problem, too much upper rpm power (but I don't think I will change my bike, it is really fun that way in the sand). Thanks for the help. -Todd

 

[bradf]

tell him to contact Ron Brown at RB-Designs. go here http://www.rb-designs.com RB's carb mod is the most significant improvement a 220 will ever see, top end as well as low end, especially after the stock pipe has been changed. There is another KDX forum where all this has been extensively discussed by highly technical experts and testers. RB posts to this other site as well. While you're at it, spend the extra $40 for the RB head squish band mod.

 

[adam728]

The carb mod and porting will make the KDX rev much higher. It's still no motocrosser, but its a huge difference from stock. I had my cylinder ported, head modified, and carb bored out by Freddette racing. Along with an FMF rev pipe and Boyseen reeds the difference is massive.

A co-worker of mine has the same bike, but stock. We went riding a few weeks ago and traded back and forth. I had been riding in 2nd gear, sometimes hitting 3rd on my bike. With his (same gearing) I was in 3rd most the time, grabbing 4th sometimes. I was going much faster while on my bike. His felt like it fell on it's face at the same point where mine really started pulling. I'd swear it pulls another 2000 rpm on top (I really have no idea how much more it revs though).

 

[bradf]

Note the difference between a simple carb bore and a carb mod. Boring only increases the bore size while a mod (as done by RB) not only increases the bore, but the slide is modified, pilot circuit modified, jetting is completely changed and it adds a divider plate which is a huge low end benefit.

 

[sasrocks]

I have the exact same problem that is starting to bug me.... I have done the searches but still not sure the answer to this question:

to what extent will the RB mod alone remedy the lack of high RPM power for the 220. My brain says porting is the major factor but I just did the top end and don't want to pull it off again.

can the RB mode get me most of the way their or does the porting need to be considered on top of the carb mode?

 

[bradf]

The factory pipe is tuned (small diameter expansion chamber) for low end. The shape and size of the pipe on a 2-stroke plays a major roll in RPM, power and range. Replacing the 220's pipe with an FMF Desert -30 (14" circumference) or a Woods -35 (11" circumference) will be an improvement. Now add the larger carb to work with the new pipe and top end is significantly increased. The -30 will be the best top end. The divider plate RB installs allows the carb to have a better idle/ part throttle signal (acts like a small carb at part throttle) and retains the low end power characteristics. The KDX has so much potential. Completing all the mods i.e., the pipe, RB carb, reeds like DFIII's, and even an RB head squish band mod, will transform the KDX into a completely different machine. It will not be overpowering, but it will have a lot more power. The power will be very strong and smooth from idle to a much higher RPM. As far as porting goes, ask CC, he knows porting on the KDX.

 

[tominator]

RB Has it nailed.

I installed the RB on carb, head mod and installed a Wiesc ( lighter than stock???). It made a tremdous diference in the bikes top end. I was considering FRP porting but after the first ride with RBized parts I decided to wait. (I have FMF rev & si, w/607s). It still pulls good down low too. I got the little airscrew thingy too ... I love that thing! If you need a more quantitative answer you should call Ron.

 

[StrokesX2]

Do the RB carb mods do as much for the 200. I know the 200 has a larger bore carb to begin with, but it sounds like they do more than just increase the bore.

 

[bradf]

Canyncarvr is the one to best answer the 200 questions. I have a 220 with all the goodies (-30, wiseco, DF3 reeds, RB head and carb and the ever-so-sweet knurled airscrew to adjust to the second sweetspot). CC has the porting too. There is a lot to the porting...A LOT!! Talk to CC first before you consider porting.

 

[xtremekdx]

I may be crazy, but maybe he's geared too low. maybe go up 1 tooth on the countershaft sprocket. then he wont have to start in 2nd gear.