04 wr450 carb problems- help please

Hey guys I got a buddy that has a 04 wr450 that has always ran perfect the 9 yrs he owned it. Not a single bog or carb issues ever, previous owner had it tuned perfect. He had it apart and cleaned it this winter and put it back together and it idles, but not well, pops badly on decel and glows the header red hot. The guy knows what he's doin and didn't touch a single jet, replaced the diaphragm in the acc pump because it was coming apart. But other than that, didn't do a thing but clean it. The only obvious problem is that the choke won't stay on and it seems to run better when the choke is held on now, which leads us to believe its lean and needs more fuel. But it has a 45 pilot jet and is turned out 3 turns. If it does need a bigger pilot, I don't understand what could cause it to need one since it's never needed one and he just really shouldn't need anything bigger than a 45 for this bike. Any input or experience with this odd issue would be appreciated since we are trying to resolve this issue quickly to go on our annual trip to Missouri in a few weeks, thanks!

There is never a reason to change jetting on a previously well running bike.......jetting requirements do not randomly change.


Replace the pilot jet with a BRAND NEW ONE and clear the passage above the jet with fishing line and spray cleaner


Get an R&D remote fuel screw for proper adjusting


If you are going to remove the carb, you should also do the required maintenece:


- new slide plate seal

- needle jet replace

-  clean/polish/lubricate the hot start and choke plungers and cavities

- apump verify (nozzle spray, free moving check ball, etc)

Edited by Kah Ran Nee

Thanks, he ordered new plungers for both as well as a new pilot jet, what could be wrong with a pilot jet that it needs replaced?



You can't get it all out without an ultrasonic cleaner.....or by damaging the fluted openings.

Cool, good to know, thanks

I would think he loosened some dirt up somewhere last time, which is now plugging the pilot circuit. Or maybe unknowingly lost the fuel screw o-ring.


Tell him to blow some carby cleaner and compressed air through the passage behind the pilot jet - if he sticks his finger over the tiny hole that sits just inside where the carburetor connects to the engine, you should be able to feel the pressure from compressed air that is being blown into the pilot passage.


Secondly, take the fuel screw out and double check that all the bits for it are still there. If he's missing the o-ring it will cause bad idle. Careful as sometimes it's just stuck up there. Clean out behind up there as well. It's definitely a good idea to buy an aftermarket one as Kah Ran Nee said. They are pretty cheap.


Hope that helps out.

Alright, he finally got his parts, replaced choke plunger and hot start plunger. Switched the old 45 pilot to a new 48. It runs fine, no popping, idles great but... It gets even more confusing, this is achieved with the pilot 5 turns out! How is this possible when with a 45 at 3 turns out, it ran perfect for 10 yrs before it was taken apart this winter?! I just don't get it...

Because there is still corrosion inside the carb; probably the pilot passage, so it is acting lean, still.

And you'd need an ultrasonic cleaner to get it clean?

You can do that, but reaming the passage above the pilot jet with strong solvent and a large fishing line usually does it.


You must remove all rubber and foam parts form the carb before attempting this....

Slide seal plate goes flat side down.

I made this mistake myself.

It looks like it should go the other way but doesn't.

It popped bad on decel like this. I mean bad!!

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