Jetting recomendations please....

Been quite a while since I've been on the list here, the big blue bruiser has been running pretty good lately. BUT, I never leave well enough alone so here goes.

99 WR400, stock but for a PMB muffler and open box.

Location is tropical, frequently in the low 90's, highest humidity possible. I am running a JD red at middle clip, seems one clip richer is slower, one leaner is slower. I'm at a 168 main, and stock pilot and everything else. The issue is that my fuel screw (easy adjust) does not alter idle speed at ANY setting. I can run it all the way in or out without altering the idle in any really noticeable way. I know my ac pump is not working right so I'm going to get one of those 80$ adjustable pumps, but while I do that I thought maybe I should change out at least my pilot jet and any other "good bets" for a better running bike as far as carb changes go.

One not so little issue that I'm wanting to fix is a habit of this thing to sputter when I shake it hard like on fast bumps. This I'm pretty sure is the float adjustment, my question is whether or not it's getting choked or starved for gas? My guess it's choking... lower the level by a mm? It also occasionally will foul out and need a lot of cranking to start.

Oh (sorry), is it possible for one 168 jet to run differently from another 168 jet (unaltered)??? I swear the other one ran better

Thanks very much!


I am at the same temp - humidity as you.

if the fuel screw does nothing, you are out of range - either way lean or way rich.

In our climate, we have to go leaner on our settings. Try a smaller pilot jet.

It sounds like you have the right needle position from what you describe.

The 168 main might be a bit fat, try a 165. Rich and the bike will stumble, like cutting out. Lean the bike will struggle to build speed, bog, sound real ashmatic.

Fix your carby - get it in full working order before playing around with jetting. You are wasting your time if you dont.

Motopower video productions just released a DVD that shown how to tune both 2 stroke and 4 stroke carbs. It covers setting the float height, changing jets, needles, clip position, fuel/air screw and idle screw. It starts with a bike that runs poorly and walks you through the tune up on both 2 stroke and 4 stroke bikes. You can find it at

Good luck

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