05 Wr450 suddenly rich!

OK, I have been working on this thing alone for the last two weeks and it is still not fixed. During my last ride my bike slowly developed what I think is a rich condition, burble and jerky at constant throttle, a black fouled spark plug, choking fumes, and poor idle. I need some help from you guys. :thumbsup:

05' WR450 settings during last ride:

Main jet: 168

Pilot Jet: 48

Fuel screw (turns out): ZipTy - 1.5 turns

Needle model/Clip position: JD Red 5th clip

Air box: Snorkel out, "punch-outs" removed

Pipe: stock, plug removed

The temperature is about the same as when I first jetted it and it was spot on then.

What I have checked / changed:

Pilot jet changed to 45

fuel screw completely closed but still a little rich.


Exhaust: all within specification but on the tight side (around 20mm)

Intake: one at 9mm all others in specification (around 10mm)

Spark plug: was fouled but now new, this almost fixed the jerky condition.

Air Filter: clean

Carburetor: removed and thoroughly cleaned, all jets removed and cleaned and all passages blown out with compressed air.

Has anyone had the jetting change so drastically that it required the fuel screw to be closed to run when the jets are within the recommended sizes? I am using fresh fuel, but could that be the cause? The humidity has been higher lately, how much of an impact does that have? Is there any circuit in the carb that that could be clogged that would cause it to be rich?

Your bike is fine but high humidity really screws up the jetting sensitivity of our beasts. Do the following:

45 pilot is low enough for high humidity with 1.5 turns out on the fuel screw. Move the Red needle to clip #4

Put in a 160 main jet on high humidity hot days. :thumbsup:

made it home all safe and sound i hope!Sorry we didn't get to ride together BUT next time watch out! :thumbsup:

Thanks Indy... My next course of action was to change the needle clip one position to make it leaner. I will also try a smaller main jet as you suggested if that doesn't work.

made it home all safe and sound i hope!Sorry we didn't get to ride together BUT next time watch out! :thumbsup:

I am glad I had my sunglasses on Tom! Your Anniversary Edition YZ502 Super Bling Bling bike was so clean and bright I was embarrassed to wheel my super piggy over! :bonk::confused::confused: Thank Ursala for the great sandwiches. We went to Westpoint the next day and had a blast. Hope to see you at Durhamtown or the Ridge again soon. :thumbsup:

Indy, Thanks for your help... :thumbsup: My jetting is now back the way it was before my last ride.


Very rich condition causing a fouled plug, poor idle with the fuel screw fully closed, hard to start even with the hot start lever.

Changed pilot jet from 48 to 45... better idle and starting but fuel screw still had to be fully closed.

Moved clip up on needle... almost there but fuel screw only 0.5 turns out???

Then I specifically cleaned the Air Cut Valve (ACV) with compressed air :thumbsup::bonk: now it is working the way I think it should. The fuel screw out about 1.75 turns, perfect idle and it ripps again.

On my last ride I stalled in a fairly deep mud puddle, it is possible that something was sucked up through the drain tubes into the ACV. Does it make sense that a plugged ACV would make it richer?

It will be getting hotter in about a month here in Texas so I will leave the pilot jet and the clip in place. Do you think this is a good idea?

You will be OK with your jetting since Texas is so humid. The ACV circuit can get clogged and it will make your jetting very rich if this happens. The guys who bypass the ACV circuit run a 42 pilot. :thumbsup:

Jetting is fun but give me EFI! I am ready to replace my WR in 2007! :thumbsup:

I agree, I installed and tuned an aftermarket EFI system on my motorhome and it seemed much easier to understand. You have a map and a O2 meter with modifiers for starting, temperature, and a few other things.

They will have to really boost the electrical output to run the fuel pump (if they go electrical).

Someone could almost put together a kit with off-the-shelf parts:

Throttle body off of a 1000cc V-twin

larger charging system from some desert racing kit

Small fuel pump like the one Holly uses in their aftermarket kit

There are several control modules like mega-squirt, or Holley... The trick would be finding one small enough.

Have you ever ran across a schematic of this carb?

I rode one of the new Suzuki Quadracers with the fuel injection and WOW. It was cold and took the gas immediately. It revved smoother than any 4-stroke I've ever seen and had no hesitation, miss, or choke out(spit and die). It is still no bike motor but I like in fuel injection over the FCR. I just hope when they put it on the bikes it will adjust itself like whats on a car. The one on the Suzuki knows when you remove the tip from the exhaust and airbox lid and thats it. Past that it has to be reprogrammed like the Cannondale's. Thats the bad part.

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