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yamaharichey

Jetting WR450

15 posts in this topic

For those of you interested like mparrish up there in Brigham City I'am about there with the jetting. Here's what I ended up with, with JD Jetting 's help, 165 main, Red needle on #5, 40 pilot jet, two turns out on fuel screw. now that 40 pilot jet might sound a little strange, but that is because I completely sealed off the air cut valve by cutting out a gasket out of gasket material and removing the little o-ring, spring and diaphram and putting the gasket in there instead. James Dean is conviced the acv is the culprit that is causing the surging, hesitation at steady throttle, but when you do that it makes the bike run rich in the lower rpm's thats why such a small pilot. He suggested that or a larger #100 pilot air jet, which no one had. Now for the results, There is absolutly no bog when you snap open the throttle, I mean that bike can be sitting there idleing and you can wack that throttle all the way and it just instantly revs. that makes more of a difference riding than I thought it would, talk about easy wheelies. and now the steady throttle hesitation at 1/4 throttle is gone, the only minor problem is it still hesitates at higher rpm at seady throttle maybe thats asking too much to expect these WR'S to be perfectly smooth throughout the entire rpm range, I don't know.

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Did you seal off both the O-ring hole and the diaphram hole when you removed the diaphram and spring? What is the highest elevation you ride at? Mine gets a little boggy when I am around 8000 ft and it is hot. Thinking of trying a 162 or 165 Main jet.

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RNH, yes I cut out a gasket that sealed off both holes, it was the size of the cap that is held on by two screws.

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I must be one of the few, My bike's jetting is perfect . (Mods) , Air box and throttle stop , M4 pipe .Bike has no bog and runs great. Surprize was my reaction when I discovered this bike was race ready. Can't say how much I have spend in time and money trying to bring a new bike up to specs., and ready to race.

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I know the 04's are better in the jetting area, but two friends have them and both do the stutter at steady 1/4 throttle. Try letting it idle then snap open the throttle all the way as fast as you can, if it doesn't bog I would be shocked.

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No bog! Power now may be helping. My bike wheelies right off idle if I slam the throttle wide open. What do the rest of the WR450's do when idling a 6 mph and you hit it? :awww: "Hunting" at steady throttle postion is normal on these bikes and since I am always accelerating or braking it does not bother me at all. Dual sporting it may be more of an issue. :thumbsup:

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Indy I thought you got rid of the "hunting" with the JD kit. I'am driving my self nuts trying to get rid of that but it still does it. So is there anyone out there with a 03 WR450 that has smooth steady power through the entire range? And I mean when you hold the throttle steady. I've had some guys tell me they don't have it, but then find out they really do if they hold it steady at a certain rpm.

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Mine is pretty dialed in (see signature) although I noticed this weekend it seems a little rich at 1/4 steady throttle now that temperatures are above 80 and humidity is rising. As far as the off-idle bog issue, just set the idle a little higher and play with you fuel screw. I discovered this the hard way after After rejetting countless times :thumbsup:

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Not sure if the "hunting" can totally be eliminated on these bikes. I wonder if the YZ's do it too? I have been trying to figure out exactly how the ACV operates. I'm not sure if just blocking the holes with a gasket totally disables it. Without the plunger in isn't that how it would be on decel? Sure would like to see a cut away view of the carb to see exactly what the ACV is doing.

Lowedog

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It takes a high vacuum to open the ACV, which means it opens on decel....therefore you want to block it in the closed position, so the plunger is in the hole. I intend to make a spacer to replace the spring so the plunger/diaphram can't pull out. Maybe I'll do it tonite....

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So maybe I didn't do it right, I just removed the o-ring, the spring and the diaphram and covered it with a gasket. I think I'll mosey on over to the jetting forum and ask James Dean, cause he's the one who recommended doing that. tune in and we'll see what he says.

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It takes a high vacuum to open the ACV, which means it opens on decel....therefore you want to block it in the closed position, so the plunger is in the hole. I intend to make a spacer to replace the spring so the plunger/diaphram can't pull out. Maybe I'll do it tonite....

I agree with you. I was told a few month ago to try it with the plunger out and when I did I found the bike ran like sh%%&&*$@##$t. I have to rejet this weekend anyway and want to try with the plunger in.

If you block the little vacuum hole only, shouldn't that keep the diaphram from opening and therefore a spacer would not be needed?

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If you block the little vacuum hole only, shouldn't that keep the diaphram from opening and therefore a spacer would not be needed?

I agree but I couldn't figure out what to use to block the hole, I thought about some silicone but I was afraid it would suck inside. Maybe a little peice of rubber, let us know what you end up doing.

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It takes a high vacuum to open the ACV, which means it opens on decel....therefore you want to block it in the closed position, so the plunger is in the hole. I intend to make a spacer to replace the spring so the plunger/diaphram can't pull out. Maybe I'll do it tonite....

I agree with you. I was told a few month ago to try it with the plunger out and when I did I found the bike ran like sh%%&&*$@##$t. I have to rejet this weekend anyway and want to try with the plunger in.

If you block the little vacuum hole only, shouldn't that keep the diaphram from opening and therefore a spacer would not be needed?

Yeah, that should work.....I was going to put some clay or putty in place of the spring. Just something to keep it from opening.

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