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Proper air mixture screw setting for the RB carb modification
(this will also be the proper procedure on a stock PWK carb also, but not as sensitive)

Part of the modification of this carb is in the low speed circuitry. The mixture screw now becomes a great tuning device. Note: it only takes a very small tweak to make a big change. Only 1/16th of a turn will make a big difference. You will be able to keep your carb tuned for changing altitude and temps. Do not be afraid to play with it, have fun.
Note! This will work with a stock carb that is properly jetted also, but will not have the great results and sensitivity as the modified carb.

To obtain the proper air mixture screw setting is as follows;

You are not adjusting for the highest idle!

Start the engine and let it warm up to operating temp, with the bike in neutral blip the throttle from the closed position and see if the engine stumbles or stalls.

Adjust the mixture screw in one direction only a 1/16th turn at a time. Blip the throttle, if it improved turn it another 1/16th turn and blip it again. If the direction you first started with makes it worse then turn it the other direction 1/16th turn at a time until you get the best response.[/b]Next get on the bike and run it in 2nd gear with the engine idling (low throttle setting with load on the engine and blip the throttle). Then try and adjust the mixture screw 1/16th turn at a time in both directions until you get the best acceleration off a closed throttle.

Finding the second sweet spot is similar, turn the screw out 2-1/2 turns and do the same fine tuning procedure as above. It’s a little tricky finding it and even a 1/16th turn can go right past it.

Hope this helps,

Ron

Hey Ron, I think the SSS is easier to find in a 3rd gear throttle roll on, it allows the engine to load longer than 2nd gear.

bradf,

Good point...., I was just trying to give the basics. There are so many people out there that think the mixture screw is a mystery and others do it the wrong way

Your post will help people with the sss.

Ron

Ok you guys are talking about the ss which I assume is the sweet spot where the bike runs good; but what is the SSS exactly ?
What is the difference and in what condition should you use it? (if you ever manage to find it)
I remember a post saying that on the SSS you get better low end, is this correct?
Thx
wilf

CM: Second Sweet Spot OK, but what does it do?

Second Sweet Spot

SSS (second sweet spot) is a position of the AS that is further out than would seem normal. On a "normal" carb the the best AS setting for idle is usually between 3/4 and 2 turns out. But on a RB modded carb there will be a SSS that is about 2 1/2 turns out that actually gives BETTER performance than the primary setting ever could. This is due to the divider plate position and the internal work RB does to the air passages like the slide and other areas. It is actually so good it gives the motor a different feel because it allows it to pull from very low RPM's, much lower than normal, and yet maintain good throttle control/response at the same time without loading up or leaning out.

This is the way I describe it

You know when you are in 3rd or 4th and you are just lugging along? Not pulling any RPM's ? usually in some tight single track, and you come to a real tricky section maybe some uphill stuff, you give a lil throttle and it starts to bog down, if you give it more throttle it'll bog worse and die

With a RB modded carb and the SSS, instead of bogging down it just pulls, it may or may not pull more revs, depending on the terrain, it just keeps on chugging along and it sounds like no other 2 stroke I've ever heard

It still totally amazes me everytime I put it to the test!

I prolly out weigh carvr by close to 100 lbs and my lil '92 takes me just about anywhere his '00 will, even when he's running jet fuel!

funny this thread describes just how my ported 220 runs and how I tune it to ride, except I use 1/4 turns. I have never had the chance to ride a stock KDX so I assumed this bike was supposed to pull from down low to high like a thumper.

It is to a point....

It's so simple to find...I think (hope?) even someone from Australia can find it!! We'll know next week!!

You will be surprised at the result if you haven't taken the time to tune in that area. The lower 1/2 throttle pull in higher gears is indeed remarkable. I notice the largest effect of a correct setting in 3rd gear at mid-throttle.

The 'other side' (if you will) is just as noticeable. If you are out in the 2 1/2 area but NOT at the SSS your bike will have a quite severe case of the 'don't run 'fer diddle's. That is where the finger adjustable air screw comes in. Bradf mentioned this in another thread..but temp changes during a normal day's ride in these parts WILL have you adjusting the air screw. With the knurled screw you can do it on the fly.

Believe it! When you find it, you WILL know it. If you get CLOSE to it, but not ON it...you will wonder what the big deal is.

It is a big deal. Find it. You will be keeping it there!! Remember...it doesn't take much to pass it up!! Like Ron said, a 1/16 may be too much of a move. Once you do find it, you will immediately know when it's off due to temps and/or other environment variables having changed.

I cannot emphasize the impact of this adjustment enough. There have been riders, having NOT found it, that have pooh-pooh'd the whole idea. Then they use the correct method to find it...all of a sudden..there's another believer in the RB-carb fold.

Krazy: I'm glad your bike runs to suit you. Your adjustment routine (1/4s) is a guarantee that however well your bike runs, it has nothing to do with the subject at hand.