Strange jetting problem


I have a strange problem with my 04 wr450.

I have read the sticky thread and tried to follow it to adjust my fuel screw.

The problem is that I need to turn the fuel screw about 3 turns out to get some kind of idle, without having to adjust the idle screw way in. I have tried several pilot jet's (48 std, 50, 52, 55), but strangely enough the behavior doesn't really change.

I have tried cleaning the carb several times. I have checked every jet, and the only thing that is not standard is the main jet (a little bigger then standard) och the needle (raised one step). Those changes shouldn't have anything to do with my problem right?

I have checked the float level, and I think it is correctly setup. Tps has been adjusted, but it doesn't mater if it is connected or not. I have replaced the cold starter (starter plunge) and the seal on the warm start. I have tried both the original fuel screw and an aftermarket screw (the o-ring, washer and spring are all there in the correct order). I have looked for leaks around the carb with start gas.

Pulling the cold start raises the idle rpm. So does pulling the hot start when the cold start is pulled (doesn't really change the ilde rpm much when the cold starter is not pulled, but it still helps sometimes when I'm starting it warm).

Does anybody have any idea what I might have overlooked? Other then this, the bike is running fine with very little bogging. Some loud bangs when coasting and lots of smaller bangs if I turn the fuel screw in and compensate with the ilde screw. I hope that by correcting this problem, I might get it a little bit smoother transition from idle to small throttle openings. It currently feels quite nervous.

Try a 45 pilot. Looks to me like the pilot circuit was made overly rich to quiet an open exhaust decel pops.

Maybe I should try a smaller pilot jet (I think I might have tried a 38, but that is quite a jump). However doesn't all the signs point to lean condition and that it in "theory" would need a bigger pilot?

William is wise, I'd listen.

You've gone fatter with no good results, what would it hurt? I think a 45 is common to use on the 04's. I honestly don't know what mine has in it since the PO did a great job setting it up: starts easy, runs great, minimum popping under decel. He said he jetted it using info off this site and I believe it.


No, I don't really see any harm in trying it, so I will see if I can find a 45 pilot somewhere tonight. After all: In theory, theory and real life should be the same thing, but in real life they rarely are :smirk:

LOL, the 38 is way too extreme. Make sure the 45 is a new or nearly new jet. Some old jet fro the bowels of the jetting drawer is questionable.

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

A friend of mine had a couple of smaller jets, so I started by putting the 45 in. Same thing though, fuel screw had to be 3 turns out. But instead of a couple of loud bangs on decel, I got lots of smaller poppings. Then I tried the 42, and bingo. First I noticed that my idle was quite high. After turning the idle down, I could turn the fuel screw in to right before 2 turns out before i noticed a slight change in rpm.

There are still some minor popping on decel and I should probably test it some more, but overall it seems to run fine now.

I also want to thank you William1. It's not often you get a reply that is spot on in under 10minutes. Impressive :smirk:

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