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Elevation Changes and Maintenance

Posted: Sun Jul 15, 2007 12:31 pm
by cyphecks
On long trips with drastic changes in elevation, is there any necessary maintenance to perform in regards to how thick or thin the air is? I assume anything that needed to be done would concern adjusting the carbs. I'm going to be leaving Salt Lake (4200') and making my way along the west coast at sea level, and then going east across the higher ground of New Mexico and Arizona until I get back down, to the relatively low south and east.
I remember the guy in "Zen and the Art of Motorcycle Maintenance" talked periodically about changes in the air and his motorcycle, and although I know its not a shop book, I thought it might give some indications as to whats needed.
Does anyone take long trips like this and service their own bikes, and maybe have some tips? Thanks.

Posted: Sun Jul 15, 2007 3:08 pm
by slimcolo
I have an 82 Honda that has the High Alt kit installed, however it falls on its face about 11K. (needs low range to continue above this)Was told that only fix is to change jets. This is impractical as hell as many afternoon rides may start under 6K and top over 13+ (sometimes 14ers) in less than 5 miles. What use is the high alt. kit if you have to re-jet several times a day? Why do they not put adjustable jets on trail bikes? Its like cooking directions for high alt. (3000-6500ft) What if your over 6500?

My Nissan (according to dealer) will adjust for altitude via computer. Bullsh!t it craps about 11.5K and needs 4low just to pull itself.

As to adjustments I use to change timing 3-10 percent from specs. Points type ignition at about 8K+. (helped with Jeep,Ford,J-D, and HD) But yes most adjustments are to carbies.

My 72 XL needed adjusted every 500-700 ft change. But it had adjustable main jet that could be adjusted on the fly. (also needed adj. for town/hiway) But it was great in all altitudes that I had it in. (2K-12.2K) Prior to adj.jet this bike wouldn't run very good below 6K. (previous owner lived at just over 10K)

Posted: Mon Jul 16, 2007 3:11 pm
by flynrider
If you were moving from a high altitude area to a low altitude area, then it would be a good idea to rejet the carbs to compensate for the air density. On a trip, you just live with it. The bike will be running a bit on the lean side down at sea level, but it should do OK.

Hey Slim, if your Nissan is less than 15 yrs. old, the fuel injection is compensating for the altitude. Unfortunately, there's no way to compensate for the thinner air (and lack of oxygen) at 11K ft. (besides turbocharging). Your Nissan is just displaying a lack of available hp at that altitude.

It could be a lot worse. Without metered fuel injection, you'd not only lose power because the air was thin, but you'd also lose even more power because of the overly rich mixture.

Posted: Mon Jul 16, 2007 4:55 pm
by slimcolo
Wasn't a prob with my Scout. (4cyl)It was underpowered but didn't lose anymore. It would go same place in 2wd hi. Ditto when I had Jeepster. (Studabaker powered) Of course those were 'real' 4wds and had hi/low in 2wd as well as 4wd, and set up for PTO. (top speed 45) They would go places in 2wd that Nissan won't in 4wd.

Posted: Tue Jul 17, 2007 6:53 pm
by flynrider
They don't make 'em like they used to :wink:

I've taken an older carbed Nissan truck over Monarch Pass, as well as my newer fuel injected version. Neither one was spectacular, but with the FI version, I was at least confident that I'd actually make it over the pass.

BTW - I had a '69 Jeepster. It came with a Buick 225 V-6. That thing would really get up and go!

Posted: Tue Jul 17, 2007 7:33 pm
by slimcolo
Did Mosquito on my GS twice. Did Monarch in all three Nissans with very little probs, they start a little higher. The probs I had was at Trunceria Peak 13 something (both honda and two Nissans same place) was able to continue with Honda in low range and 4wd in low range even though road didn't warrant. (the bad spots were below this)

Want to try Blanca Peak (14.2K) later this summer with Honda (this is one of the few 14ers that are not in a Wilderness Area)