James Dean

Thanks again for the help with jetting. I had a thread going before the "TT Crash".

After reading all the jetting and BK mod posts, I finally put in the screw. Without the screw, the fuel squirt was 1.7 seconds, and seemed to be over a foot long. Per BK I turned it down to .34 sec. (BK says .3 is right).

BTW, 80% of my riding is above 6500ft. '01 yz426, Big Gun SDS exhaust with s/a.

Before the screw, the best jetting was 162 main, (perfect plug, 5th gear @ 80mph on pavement), stock needle at clip #1 (lean), #38 pilot. Wierd huh? Although the best I could get, this was not GREAT. Still some stumbling, and hanging idle (lean).

With the squirt turned down to ~.3 sec. it took me a while to straighten out the jetting, but was well worth it.

Now I have: 162 main, stock needle @ #3 clip, # 40 pilot @ 3/4 turn out. I may try the #38 pilot again. Acc. pump turned off!

Sunday for the first time in about a month, I actually rode with other people! (I actually rode ~300 miles in that month). And also for the first time, I wasn't concentrating on wacking the throttle,tweaking the carb, wacking the throttle, tweaking the carb, etc, etc. I just rode and had fun . The guys were pretty fast, two '01 wr 426's, a cr250, and a yz250.

(see post "drag racing...")

The bike ran great. Started fine, even after a couple of stalls. Never coughed or missed a beat. Pulled everybody on the pavement drags.

What suprised me is that last night I pulled off the sub frame, and found the air filter almost plugged with dirt, (my bad), but also I had the acc. pump turned off! Absolutly no squirt. I had been turning it down gradually, but never checked by looking at the squirt.

What do you think about this? I will be checking by slowly increasing the squirt, but I know there is a point where it hurts performance. After I set the squirt at .34 sec, I increased it by 1/4 turn (on the new screw) at a time. By the time I was 1 turn out the stumble was getting worse, so I slowly leaned the squirt. I didn't realize I had shut it off.

I am suprised it ran so well. I rode it hard on all kinds of trails. I even cleared a 20ft table top several times. My first time jumping, except for waterbars. (I'm 46). I can see where jumping is like a drug.

Question: Should I expect more punch with some acc. pump? I know it was put there for a reason, but it ran awsome without it.

I am very interested in any comments/questions.

I have to tape up my two fingers now and put them to bed. Sorry this was so long.


Rick Fuller

'01 yz426

'81 490 Maico


This is an interesting point. If the jetting is working dialed in well, the pump is not required nearly as much.

You have a higher altitude and the dirty filter (bad you) making the mixture richer. This is the same result that I found with zero pump (clean filter though :) ). A richer clip position will allow wicking the throttle open just as fast within a limit. But this can be too rich for real riding conditions. When it runs clean enough, the throttle can't be snapped open quite as hard. This is when a small amount of pump stroke gets the snap AND clean running with better torque and overall performance. The fact you rode it without the accelerator pump leads me to think you either had it on the edge of rich (with caked filter) or adapted your riding a small amount to roll it on. This gets to be subtle differences here. Either way, with a clean filter and about .5 sec squirt you should get the best performance. I would also not go smaller on the pilot jet and stay with the pilot screw near 1 turn.




Rick Fuller

'01 yz426

'00 yz426 destroyed by fire in desert race 4/22/01

'81 490 Maico

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