2000 426F Issue: Hesitation

Now, I suppose I could have posted this in the jetting section, but I'm not sure exactly what is the problem. I'll throw out the disclaimer right away that I'm not very mechanically inclined. I like riding, but don't know too much beyond the standard maintenance items.

Anyway, I noticed while I was riding last weekend that my 2000 426 was hesitating when I would crack the throttle while it was idling. I didn't notice it when the RPMs were already up part way, just when I rolled on it hard from idle. Is this a jetting problem, and if so, what do I need to do to fix it, or what do y'all think?

As always, thanks in advance for your help!

This, my freind, is the infamous Yamabog. Us old guys with the '99, '00, '01s have dealt with this problem in various ways.

I don't think its all in the jetting. Has a lot to do with what kind of riding you do and where. I ride mountain and desert trails, from 0 elevation to 10K. My bike works great across the board, although some may argue this. This is what I did....

First of all I lowered the pilot one size (seems that stock jetting is designed for WFO and usually us civilian knucleheads don't WFO all the time). Added a long Storm airscrew (pilot needle) for last minute altitude adjustments

Next, add a accelerator pump cover/atomizer. I use a P-38 Lightning (I think Boyeson has one too).

Last, but definetly not least, add a PowerNow, or better yet, a FreePowerNow...search TT for the design and build instructions.

Better aftermarket air filter is also a good upgrade. I liked the No-Toil filter(s) and system for years, but lately I like the K&N. Anyways, my Yamabog has been gone for years and my bike has a snappy throttle response. :thumbsup:

Thanks Dr. T.

I just ordered a new Twin Air filter and it arrived yesterday, but I haven't reduced the pilot by one size. I'm certainly not a full-out sort of rider, and I've never really noticed the bog before, so it must not bother me too much. I just figured I should probably dig into the issue and see if there is a fix.

As I mentioned, I'm not mechanically inclined...I'm not even sure how to change the jets. I've got a manual, so I should be able to follow along. I've never really taken apart anything more complicated than my lawn mower. Is changing the jet easy? (Feel free to laugh at my expense!)

You can actually change your jets with out taking the carb off the bike. Just rotate it (after loosening the boots) and there is a little plug/cover on the bottom that will expose the main and the pilot jets. Intall a longer pilot screw too, the stock one needs a little screw driver to adjust, the longer aftermarket ones use your fingers (about $10-20, various makes, ZipTy, Storm)

You can make a FreePowerNow very easily, I did from instructions I found here on TT. Anyone with skills greater than a 6th grade Crafts Class can make one. All you need is a thin file, a coke can (or thin aluminum) and a couple dabs of epoxy.

The accelerator pump cover can also be fitted without removing the carb...follow the instructions that come with it, a P-38 Lightning is about $30 (maybe $40) and, like the PowerNow, makes a difference like night and day. :thumbsup:

One other thing that causes the problem is the fuel spray duration when you crack the throttle from idle to wide open. Some of the fuel spray durations on the 426's were 1.5+ seconds and they were supposed to be like .3-.5s. There are other ways to deal with this one thing you can do or look up at least is to check out the BK Mod thats what i did and i have no bog at all. And like stated earlier get an aftermarket Fuel screw for fine tune adjustments. I have a 2000 426 I did this to it and the bog is gone forever.

I have heard of aftermarket fuel screws falling out of carbs, so I did what Motoman393 suggested on his website.


Go to the tech articles and click on the fuel screw one. I did the one with the brake line "adjust on the fly fuel screw". It works really well and stays in! Do the BK mod as that usually takes care of the bog.


I`am in Fortworth if I can help.


You need to do look at the BK mod, and the 01 needle. I think the James Dean Jetting kit has a needle that is similar to the 01 needle, plus assorted pilot and main jets.

I did the '01 needle mod (all by itself, no other mods) and it made it worse, made the carb richer when it needed to be leaner. Also the accelerator pump squirt duration mod, the one where you modify the accel pump arm and limit screw (as I recall that one is a pretty sketchy mod, bending stuff, drilling stuff) is totally not needed after the P-38 (or the like) is installed.

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