elevation on jetting, effects?

[creed82]

Hello friends. First, want you all to know I searched before posting. I just purchased a pristine 91 blaster from the orig owner. To her knowledge, the jetting had never been messed with. The bike is all stock, and original. I live at 4600 ft and the bike runs great. You can see videos of it running on YouTube if you look at my channel "nevertoooldtohavefun", it's the blue/white blaster, not the yellow/white one.

Anyhow, bike runs great at 4600 feet. We take it to the mountains this weekend and I notice it falls on it's face under full throttle, higher RPMs, at above 7000 ft. It figure it's rich and pull the airbox lid. It runs great! Huge difference. Now I'm back down at 4600 ft and wondering, if it is stock/original with the 230 main jet, am I safe leaving the lid off? Does it need more jet with the lid off? Haven't plug chopped yet.

Foam filter, all stock with airbox lid removed, 91 gas.

Thanks.

 

[BlastfromPast69]

Im pretty sure if you take the airbox lid off you go up 1 to 2 main jet sizes...

 

[Blaaster]

If it is all stock then a #230 jet would run rich at 4,600 ft.

Taking it up to 7,000 it would be running really rich, and as said, taking off the lid will emulate 2 jet sizes.

I notice that you have a foam filter which could breathe a little better.

The only true way to tell the jetting is as you know, by a plug chop.

You may well find that the #230 main will be fine at 4600 with the lid off, but who knows as temperature and humidity also affect jetting.

You may find that when the weather is warmer that a leaner needle setting could be used.

Plug chop to find out, at WOT and 1/2 to 3/4 throttle as well.

 

[Larry's Shee]

http://www.blasterforum.com/carburetor-138/effects-elevation-air-pressure-how-jet-accordingly-39872/

Write-up on this exact topic.

 

[creed82]

Very helpful. Thanks guys, much appreciated.