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Altitude adjustments;

C

CalgaryBikeBum

Active Member
Is there a standard chart to look up what jet you should use based on altitude. Here in Calgary Alberta Canada we are at 3740 ft above sea level. I have done the SE upgrade and the 95 Big bore upgrade and now I"m down to figuring out the jetting for the carb. I was gonna go to the dealer and ask them what they jet the carb over stock for our altitude when they do the upgrades but not sure they will want to help me? Being logical I would think that the change should be the same at whatever altitude. In other words, if you are going up 2 jet sizes at sealevel because of the upgrades you would go up the equivilent amount at my altitude? The trouble is know what that is?
 
I've never seen a chart but one could exist. Your problem with jetting for altitudes would require smaller jetting than used at sea level in the same bike. The higher the altitude , the richer the mixture would be with the same jetting in a carb.
If a carb used as a base line a #46 jet at sea level, chances are that you may need a #44 or #45 or even smaller depending on the altitude just as an example.

Here's a quick test that will tell you if you have to fat of a jet in the top end....
Run the bike through the gears into third gear and run third up to 60-70 MPH full throttle, then chop the throttle about 1/8 to 1/4 back and see if the bike either surges ahead or stumbles then recovers.

If it surges ahead, your jetting is lean
If it stumbles and recovers , your jetting is rich
If it makes no difference, you're pretty close.

As far as the low jet, generally if the idle screw is more than 2 1/2 turns open from lightly seated, the low jet size is generally too small and can be increased to the next size. A readjustment is then required repeating the idle mixture adjustment screw.
 
Ok. Thanks Glider. I kind of knew that I would be rich due to the lower then sealevel oxygen level here but wasn't sure what jet size. I will still try and gleen the info from the dealer as they must have done hundreds of these upgrades here and probably know exactly what to do with the jets from stock. What would the norm be (if there is such a thing) when upgrading to the Screaming Eagle air cleaner and pipes. I"m sure the 95 upgrade has a bit to do with it too but lets just deal with the SE pipes and aircleaner?
 
Just take a nice ride on the scoot and then grab a cold one and kick back. Oh wait....you said altitude adjustment, not attitude adjustment! Sorry! :D
 
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