FAQ Topic: 33mm carb vs 35/36mm carb

[Michelle]

My 220 has a 33mm carb, is this better than a larger carb?
No. The 200 has a 35mm carb which is possible to bolt straight onto the 220. A cheaper option would be to bore the 33mm carb out to a 36mm with a divider plate.

It is not just for 220s either: In the words of Carncarvr: “How it changes the 200
Better everything. You will not be disappointed! As good an improvement as a pipe.
Going from 35mm to 36mm is going to hurt overrev? No.
Why not buy a larger bore carb?
Cuz that carb still would not have the divider installed, would not have the jet screen cleaned up, would not have the TV machined.
Besides not fitting for diddle.”
http://www.dirtrider.net/forums3/showthread.php?threadid=33209

Brush:

Michelle,
I disagree with the response about the 33mm carb. The answer makes it seem that every 220 owner should run out and swap their carb. The smaller carb is there for a reason on the 220 and that's to make it a low-end torque monster (at least in comparison) to the 200. The tradeoff is peak HP and top end performance. The FAQ answer should touch on the tradeoff issue: If you run out and put a larger carb on, yes your bike is going to rev out more, but you may also see some low end disappear. The 35mm KDX 200 carb is only "better" if the tradeoff is worth it to you.
There are offsetting things you can do: For example an FMF pipe, airbox mods, and aftermarket reed valves may boost the overall power enough that the percentage of power shifted away from the low end is somewhat masked because the overall power has been increased.
The mod that comes closest to "something for nothing" is the RB Carb mod, since the divider plate acts as kind of a bi-focal lens for airflow, mimicking a smaller diameter carb at 0 to 1/2 throttle for better low end response, yet opening wide for more airflow at full throttle.

 

[skipro3]

I have to agree that there is no need to do anything to the carb other than to correctly jet it on a 220 if you are using it for what it was designed for: Riding that requires torque. I just spent the whole day at Foresthill OHV in California with other KDX200's and KTM300's. These riders are good, great in fact and I haven't ridden a dirt bike in 15 years. They thought they would have to continually wait for me and that I would tire easily. I ran with them all day long and I have to give credit to my FMF KG-35 pipe, airbox lid removed, countershaft sprocket dropped one tooth, and a Fredette torque ring. I lugged that thing around all day long because I got tired shifting so much. Don't think of the 220 as a punched out 200 any more than you would think of a 250 as a punched out 125. Work on enhancing the bike's main forte of torque and enjoy being lazy with shifting. If you ever get the chance to look inside the barrel of a 200 and a 220 side by side, there is a world of difference. After today, for the life of me, I can't imagine why I would want any more top end power when the low end is what the bike is designed for.

 

[r.2 stroke]

Hey Skipro 3,what jetting,needle clip position and airscrew position do you use on your 220?

 

[skipro3]

Here is what I'm running, why I am running this setup, and my future plans.
Pilot: 38, Main: 145, JetNeedle position: 2, airscrew: 2 turns out.
Here's why: I ride between 3000 and 6000 ft. elevation. I ride very tight courses, single track through woods and when there isn't trees, it's rocks and steeps. I rarely get out of 3rd gear and I am rarely more than 1/2 throttle, usually 1/4. I have set the bike up to take advantage of the 220, namely torque. By running rich, the extra fuel helps cool the engine. By running relativly slow speeds, there isn't a lot of air flow over the radiator. I plan on putting in a set of Boyesen #607 reeds. When I do, I will start to set my Pilot and jet needle leaner. I find that 2 turns out on the airscrew, helps restarts on a warm engine when I stall. In the past I have found that 1 or 1.5 turns makes the bike start great stone cold but floods with any throttle at all, and / or in gear. Two turns and I can start the bike in gear (using clutch), and 1/8 throttle. This helps a lot when I am not on flat ground. There is nothing worse than to kill the bike on a hill. I'm too weak to hang onto the bike with gavity working against me and try to start this tall beast. My setup and I grab the clutch, 1/8 throttle, kick once, feather clutch and gas, get the he...ll out of there before my buddies find me and use me for traction.

 

[Michelle]

My 220 has a 33mm carb, is this better than a larger carb?
A 220 has the smaller carb to assist with the low-end - part of the reason the 220 is a torque monster. The 200 has a 35mm carb which is possible to bolt straight onto the 220, but you may lose some of the torque of the 220.

A cheaper option would be to bore the 33mm carb out to a 36mm with a divider plate, which acts as kind of a bi-focal lens for airflow, mimicking a smaller diameter carb at 0 to 1/2 throttle for better low end response, yet opening wide for more airflow at full throttle.

There are offsetting things you can do: For example an FMF pipe, airbox mods, and aftermarket reed valves may boost the overall power enough that the percentage of power shifted away from the low end is somewhat masked because the overall power has been increased.

In the words of Carncarvr, boring the carb out is not just for 220's either: “How it changes the 200: Better everything. You will not be disappointed! As good an improvement as a pipe.
Going from 35mm to 36mm is going to hurt overrev? No.
Why not buy a larger bore carb?
Because that carb still would not have the divider installed, would not have the jet screen cleaned up, would not have the TV machined.
Besides not fitting for diddle.”
http://www.dirtrider.net/forums3/showthread.php?threadid=33209

{- does that make sense now? Anyone want to add more or clarify it further? - I did, but now it's left a question in my mind - if I put the smaller carb on the 200, would that give it more bottom end?} If anyone comes across more threads that could be useful, yell out, add them here, it's a bit hard to work on the FAQ until the search function is functioning again and I'd rather have a topic sorted out to satisfaction than start trying another one. Plus I've been busy with other stuff ;)
-edited the post further. I'm not happy with it, so leaving it till we can search properly again ;)