Is there such a thing as "All-Purpose" jetting

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May 17, 2003
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#1
I have a stock '01 xr 400 and have been noting all the hub-bub about jetting. I used to ride a Suzuki 250 quadracer(10 years ago) and never jetted and never fouled a plug. Now I read about burning holes in pistons. I don't want to have to change my jets every time I go somewhere. I live at 3200ft and will ride here and at 2200ft mostly, with an occasional trip to the mountains ~7000ft. Won't be riding much below 50 degrees F or above 90. I tend to cruise along in 2nd or 3rd with occasional forays into 4th (5th? Do I have a 5th?). I do like to root around in 1st range. I'm not much of a speed freak. Humidity usually runs around 20% here. I fouled a plug the other day and it was black/dry.

Is there a "do-all" jet for my situation so I don't have to change it everyother weekend (I wish, maybe everyother month)? On the other hand, I don't want to trash something and have costly repairs. Jets are cheap and I'm not that lazy.
 

atc3434`

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Nov 1, 2001
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#2
Well, in short, you can get away with running mostly the same jetting in most cases. With your extreme changes in altitude, it might be a bit interesting though. I haven't had a lot of experience with alititude vs. jetting. However, I can go the whole season with one set of jets in my YZ125, which is pretty generous of the bike, considering it's right on from about 50 degrees to 85. Over 85, its too rich, and will start to load up and fuss a little. Under 50, well, my hands get cold under 50, so I dunno... its never leaned back too much, never got anything close to a lean bog.

In your situation, you've got another thing going for you. An XR400, I would think, being a tamer 4 stroke motor, would be pretty forgiving about jetting. I'm curious, what conditions were you under that you fouled a plug? Although its defintely not underheard of for a 4 striker to foul a plug, you've got to be noticably rich to do so. You'll notice, as you get higher in altitude, your jetting will start to fatten up, as the air is thinner, so less oxygen, so more fuel to oxygen ratio, rich.

Perhaps if you got to a happy medium for your usual conditions, you'd be ok being a little rich at the higher altitudes. BTW, I don't think you need to be concerned about frying holes in your piston. Thats much more a 2 stroke thing, and is the result of too lean jetting, mostly too lean on the main. An XR is about as reliable as they come, you wouldn't be able to ride it if you were lean enough to melt her down. Hope some of this helps.