Fuel usage, and cutting out bad.

[apolloant]

Been a while guys. New one for ya. When I lived at 2600 ft elevation, my '79 xs1100 started acting up a bit, missing on one cyl, till I revved it out, then ran o.k. Now I live at 3600ft, and I'm getting 50 miles to a tank, used to be 120 or so, and she's cutting hard from 3000 to 7000 rpm. It's a stock carb set-up, 145's, with Mac turn out exhaust, which are crap, I know. And of course, a k+n. Any ideas?

[FJ111200]

Crap Yank fuel? No wonder the stuff is so cheap. Ha ha ha. K+N won't do any harm, and it's not like you are up in the Andes.

[Crazcnuk]

You are likely running too rich, due to the altitude.

The K&N will help, perhaps even drilling out the airbox. If that doesn't help, try lowering the float levels 1mm from stock height?

[FJ111200]

Mmm, big altitude. Metres maybe, feet, don't think so, unless it's that crap Yank fuel.

[LoHo]

My XS did fine at over 8000ft during the Bozeman rally, and I often ride from sea level to 5000ft without issue, so I doubt 2600ft is a problem.

I would look at the vacuum advance. My wires were powdered inside the insulation and would work off and on for a long while. On the plus side, I fixed everything else before I got to the real problem!

[Crazcnuk]

I don't think the altitude itself is the issue, I think it's that many of our bikes are way out to start with, and the altitude just makes it worse.

[prometheus578]

Stock jetting is 137.5.
You're up three sizes to 145's.
Yeah, I know.. the after market exhaust...
Try dropping you jetting back down to maybe 140.
Higher altitude means less air... bike running rich. That's probably where your fuel is going.
You made no mention of your spark plugs.
Chances are they're black, sooty and barely working.
Shows a rich mixture.
Lean the mixture out with smaller jets.