Topic: carbs and altitude

[KevinD]

I am planning on a four day trip on the bike and will be going from Phoenix altitude of 1,086 and maxing out at 4,327 Sedona.  I am wondering if I am going to have to worry about the carbs at that difference in altitude and if so what type of knowledge or prep is needed to deal with it.  If anyone has done this trip in AZ let me know what I can expect. 

Thanks,
Kevin

[riverfever]

I live at 9,000' and a ride to Colorado Springs is a difference of right about 3,000'. Last summer I was pretty close with the tuning (I've only had this bike for two years and the first summer it wasn't really rideable) but you'll be opposite of me. How are the carbs tuned now? For my conditions out here I have to get them in a bit of a sweet spot so that if I ride down to work (in CO Springs) it's tolerable. With last summer's tune if I ran up to 10,500' to a nearby town the motor would start acting up and eventually I'd lose cylinders. If your plugs are looking a tad rich right now then maybe drop them just a touch and run a bit leaner so that things will even out at altitude. I'd also bring along extra plugs just in case they foul out.

[Jerry Rxman Griffin aka MuthaF'er]

An extra set of 1 size smaller mains wouldn't be a bad idea to have with you in case. I wouldn't worry about a brief jaunt like your's. You'll probably be fine. That extra set of plugs is also a good idea. If it starts the get pissy with you just drop a gear and clean off the plugs with some rpms.

Like River says, I live in Colorado Springs at 6900'. My bike was jetted slightly rich at 115's. Going up it would try to load up a little if I bogged it. It made it up Mount Evans at 12,000+ however I kept it in 2nd or 3rd most of the way as it is slow going. Heading down just pull in the clutch and coast ;-)

4327' is not high altitude unless you are rich at 1086'.

[riverfever]

Jerry that's pretty impressive you took yours up to Evans!

[scottly]

4327' is not high altitude unless you are rich at 1086'.

Correct. No point in re-jetting for higher elevations if it's correct at 1000'. I've had my bike over Monarch Pass (11,312') and Independence Pass (12,095') with jetting that later proved to be way rich at 4500', without fouling plugs. The power loss at elevation can't be corrected with jets; there is simply less oxygen to burn.
Kevin, what route are you thinking of taking? I-17 is the worst possible choice! 

[KevinD]

I am not sure of the route 100% yet.  I guess a couple friends from outta town and a couple in have researched out the best rides in the state.  I was contacted outta the blue and invited so...  I'll post once I get some info.

[cameron]

oh hey- I was in your other thread.

I Live in Tucson. and I had a noticeable change in performance last time I rode up to Flag- but never any problems at only 4000 feet. And as mentioned, it was nothing that running her a little hot once didn't cure. If you go higher, just anticipate not really having the same power you are used to. Its like if you left your choke on a little bit... but you shouldn't have to change anything.

[KevinD]

oh hey- I was in your other thread.

I Live in Tucson. and I had a noticeable change in performance last time I rode up to Flag- but never any problems at only 4000 feet. And as mentioned, it was nothing that running her a little hot once didn't cure. If you go higher, just anticipate not really having the same power you are used to. Its like if you left your choke on a little bit... but you shouldn't have to change anything.

yeah I did the double check and phoenix 1086 is lower than tucson 2389.  Flagstaff can hit 6909.  Kind of a drag with that much difference between phx and flag.  I am riding with some friends that have newer roadking harleys.  My 750 is not going to be done in time.  Checking the exact rout tonight.  Will post to see what should be checked out on the route as well.

[harisuluv]

oh hey- I was in your other thread.

I Live in Tucson. and I had a noticeable change in performance last time I rode up to Flag- but never any problems at only 4000 feet. And as mentioned, it was nothing that running her a little hot once didn't cure. If you go higher, just anticipate not really having the same power you are used to. Its like if you left your choke on a little bit... but you shouldn't have to change anything.

I'm in Tucson too, how come I don't know you yet?

[jcarthel]

I made it up Pike's Peak without rejetting. I had no problems. At about 10,000 feet, I did like Jerry did, revs up and 2nd or 3rd gear. For those of you that don't know, Pikes Peak is 14,110 feet high. The young sweet thing at the base who took my payment to ride the mountain said that my bike was "cool and she had never seen one like that." Justin

[Pat_at_APE]

My daily ride starts at 4000ft, up to 5000ft and then down to 2200ft.  Reverse that on my way home.  No problems with the carbs at all.   

I do ride down to sea level and up to 7000ft on a regular basis. 

Pat at APE

[camelman]

I took my 350f fron sea level to 8000 feet and didn't have to rejet. I only pulled the airbox lid. The pressure differential ratio through the carbs stays about the same, but air density drops, with increasing altitude. If you notice a drop in power, then it's due to running rich from the thinner air. If the bike runs worse at altitude, then try pulling your airbox lid. Shouldn't need to rejet.

Camelman

[Dino]

That change in altitude calculates to a 10% change in atmospheric pressure. Not enough to be concerned with really.  If you're dialed in to 14.7 to 1air fuel ratio now, you'll be at about 13.2 to 1 at altitude.
http://www.altitude.org/air_pressure.php