02 WR426F First Ride & Carb Issue on Decel

Hey guys,

I have a (new to me) '02 WR426F and I rode it off-road for the first time last Friday down in Baja. What a frickin' rocket! This bike is amazing! So much fun to ride. It seems to have a never-ending powerband, which I found out by almost looping it off a little knoll jump because I opened the throttle too much on take off.

Anyway, I have questions about why the carb doesn't seem to be working properly on decel after the bike is fully warmed up. The bike has had all the mods done to it before I got it, including richer jetting, but I don't know what the sizes are.

On deceleration (closing the throttle completely) after running at high speed, the engine rpms do not drop fully when slowing down or stopping. It doesn't allow the normal compression braking that I'm used to with large 4-strokes. It will eventually come down from this "temporary" fast idle after about 10 seconds after being completely stopped (no forward movement).

What do you guys think would cause this? Does this sound like an incorrect idle screw setting, maybe too high? Is the fuel screw out of adjustment? Could it be the wrong size pilot jet? Or is there something wrong with the slide?

I'm new to the Yamaha world and have no experience with flat slide carbs. Not having the engine slow the bike down when I let off the throttle has me a bit concerned.

Any feedback is really appreciated.

Remove your carb slide and look at it under a very strong light. It is highly likely it is about to break and potentially ruin your top end.

I have not heard of this issue on newer bikes but recently there has been a rash of this on the 98's 99's. You are running high revs because its lean. Its lean because the slide is stuck slightly open. Giving the throttle a little blip temporarily cures the problem until you ride WOT again and then it starts all over. Very disconcerting and somewhat dangerous.

Why it happens is not fully understood but the carb slide seems to flex and creates hairline cracks which then inhibit its movement on closing.

this thread has all the info

slide plate thread


I had the same problem (exactly as you described) with my 98 WR400F:

I could not understand what was causing this so I went through the process of changing the filter and cleaning the carb.

In the end my bike started cutting-out so I took it to a dealer. The carb slide had indeed broken (luckily no bits got to the valves) and it cost £70 for a replacement. The dealer said they used to cost £99 (the robbing Bar Stewards).

The bike now runs like a dream.

B.T.W: there was another 98 with exactly the same problem at the dealers when I was collecting my bike.


Right now it's 2 to 1, slide vs. the pilot screw. Sounds like a tear down is in order for me. I've done it twice on my XRL, but haven't attempted it yet on the WRF.

Thanks for the input.

Check your pilot screw adjustment. sounds like it's little to far out . turn in 1/4 turn then run her. when the bike is running at full temp. the bike should idle down just fine, if it don't turn the screw out some more 1/4 turn at a time. :thumbsup:

My 450 did a similar thing.It ended up being a tight hot start cable.I just re routed it so it wasn't pulling tight.The carb slide is fairly easy to check.Just remove the carb so you can pull the slide out the top.

So turning the pilot screw in (clockwise) will lean out the pilot circuit and increase or decrease the rpms?

And turning the pilot screw out (counterclockwise) will richen the mixture and decrease or increase the rpms?

Not sure now. A little help is needed here guys.

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