carb rejetting

[mrutah12]

was wondering what the rule of thumb is for rejetting carbs i am 355 ft below sea level was wondering if i should rejet my carbs i am runnning a 4 into one exhaust and a k&n filter thats the way i got the bike from my freind that lives in utah he delivered it to got part of my starting problem squared away got my new coils yesterday from mikes xs just need to get new wires and that will be good to go on that end but did also find out my voltage regulator is not working putting out about 14.85 to 15 volts at 2500 rpm and the lights flicker at an idle when it idles that is but any how i got off the subject to rejet or not to rejet that is the question?

[red bandit]

If it was properly jetted for Utah, you will probably have to rejet. We don't know what bike you have, so we cann't tell you what jets to use... Fill out your signature, yr, model and whatever else, the more detail the better we can help. Course you probably don't want some of our help!!

[79XS11F]

Other then the correction that was necessary for the pipe if that was even required Re-jetting really should not be necessary should it? Is the CV carb not supposed to auto correct for altitude changes? Is that not the idea behind them? I would think that if the carbs are jetted properly for the pipe you should be OK.
If however jetting is necessary based on the addition of the pipe you will likely automatically have corrected for your location when the bike with that pipe is running well.
Someone correct me if I'm out to lunch on this.
Rob

[bakenath]

I am putting k&n filters on my 82 XJ11 with stock carbs and stock exhaust (I may switch to MAC 4-2 or Jardine 4-2 if it is compatible with my 82). I am located in Pocatello Idaho with elevation at 4365ft. I will be travelling this summer to several locations (boise 2700ft for 1 week, soda springs 5840 for three weeks). I have four questions:
1. Do I change pilots and/or mains?
2. What do I change them to?
3. Where can I buy them?
4. Any other precautions when doing this job.

You guys are all great! Thanks for your help.
Nathan Baker
801-649-3029

[TopCatGr58]

Hey there Utah,

You didn't mention what jets are in there NOW?? The PO may have already rejetted?? IF the po rejetted, don't know if he knew to take his altitude into consideration, but your altitude is essentially equivalent to sea level. The jetting guide would suggest 2 sizes for pipes, possibly 1 for the K&N filter, but maybe not! I ran 4-1 pipes for many years....(in my ignorant youth) without ever rejetting at sea level, ran fine....full redline, and no burned pistons, but this was with stock airbox/filter.

With Indy filters, had bleach white plugs, went up 3 sizes to get plug color. What do your plugs look like now??
T.C.

[mrutah12]

rejetted

hey tc glad your back. my bike has stock factory jetting when i got her here to texas i cleaned carbs out and looked at jetting and it has been jetting confrimed this with my service book havent put new plugs in yet old plugs are black and fouled from me trying to start it when my picksup where all screwed up just cleaned them to see it would start and thats as far as i have gotten so far have new coils and wires ready to go waiting for fuse box from you thats about it

[posthuman]

The varous guides on here about Re-getting are not explicit about "Do I change pilots and/or mains"

Yes they provide a formula: If X then up 2 sizes minus 1, unless Y...

however I haven't seen exactly WHAT jets are changed.

raise a needle? wassat?

[TopCatGr58]

MrUtah,

Because the bike was at higher elevation, it would have been naturally a bit richer with the thinner air, and so that's probably why the PO didn't need to rejet, but at sea level, the air is much denser, and you could run a little lean. Stock is 137.5, 3 sizes would take you to 145's, and you can tweak the floats and slide needle and pilot jet screws after that. The guides and others have recommended getting the MAINS right first, full WOT response to redline, and plug color check, and then tune the transition and pilot circuits to suit performance.
BTW, your fuseblock went in the mail today as promised, should get it in a few days!

PostHuman, if you'll look at this tech tip you can see examples, photos of the main and pilot jets, and the vacuum slide needle! I'm sure there are other tips that show the carbs without the bowls on that show where the MAIN jet and Pilot jet towers are!
T.C.

[posthuman]

TC that article at link is PERFECT!

make it sticky

thanks a million