High altitude jetting?

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robin1731
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High altitude jetting?

#1

Post by robin1731 »

Anyone here live at ~9000 ft above sea level? If so what kind of jetting did you do to your wing to make it right? Just fuel jets? Air jet changes?

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Re: High altitude jetting?

#2

Post by desertrefugee »

Can't give you jetting specifics, Robin, but I can tell you that not too many people live at 9000 ft. I have ridden to and beyond 9000 many times. Really, all that happens is that the machine is down on power. No coughing, sputtering, etc. Just weaker. My old '84 still got the job done, but required quite more of a twist of the wrist. The Valk has enough reserve power that it's almost not noticeable. (Almost). Certainly not a concern for travelling.

I personally wouldn't re-jet unless I lived at least 4k feet higher than I do now (~1500). We make frequent runs to Prescott, Payson which are both around 5000. Undetectable difference. Add another 2k up to Flagstaff or anywhere on the Mogollon Rim and mileage drop-off begins to be noticeable on the Valk. I don't feel power loss until 8k or more. The 1200 power loss was noticeable by 7000.

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Re: High altitude jetting?

#3

Post by dontwantapickle »

I live a 5000 ft. and regularly ride 10,000 ft. - none of my bikes have ever been rejetted.
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Re: High altitude jetting?

#4

Post by rcmatt007 »

I just remember going that high with a hack on my 78.... the very definition of extreme anemia
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Re: High altitude jetting?

#5

Post by dontwantapickle »

A bike jetted for sea level will still run when elevation rises.
A bike jetted for the mountains will be too lean when you go down in altitude,
and bad things will happen.

I believe that and engine loses about 3% hp for every 1000 ft. in elevation.
Yeah, an engine will feel less powerful up high, (because it is).

A bit rich when running at altitude isn't really a bad thing,
it can actually keep your engine running cooler when pulling that huge grade.
And, you can use lower octane fuel! ....... a big + for cheapskates like me.

FWIW:
In 2008 I rode my Valkyrie on both the Lowest and the Highest roads in North America with stock jetting.
Lowest = Death Valley elev. - 242 ft.
Highest = Mt. Evans, CO elev. +14,130 ft.
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Re: High altitude jetting?

#6

Post by salukispeed »

Sometimes to lean the idle mixture a touch can help clean/improve the idle and even that reduces the total fuel flow a tiny bit but you need to fatten it back up once back to the flat land
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Re: High altitude jetting?

#7

Post by robin1731 »

The reason for asking. I hah a guy contact me about a rebuild and he said he was at 9000ft. Didn't say where he was. I know when racing we build/built a totally different engine. Enough changes to just have a different one rather than swapping parts in the other engines.

That is all the info I have from the guy. Usually get more in to specifics after they send me their carbs.

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and a rotation of various purchases
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Re: High altitude jetting?

#8

Post by frankroche »

According to Mike Nixon website if the bike has CV carbs you shouldn't need to enrich it. CV carbs operate by using the difference is atmospheric pressure at whatever altitude you are at and the vacuum on the other side of the carb diaphram.
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Re: High altitude jetting?

#9

Post by OCR »

Correct, but even cv carbs will perform better if jetted for at or near the altitude that they normally will be run at.
The caveat is that when going to a lower altitude, they will be overly rich and need to be adjusted or jet changes.
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Re: High altitude jetting?

#10

Post by CYBORG »

A gentleman mentioned going from
Death Valley to Mt. Evans. I have done both places without a carb change and did not notice any real difference in performance
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Re: High altitude jetting?

#11

Post by OCR »

True, but then if you changed jets for altitude, then you would notice an improvement at altitude.
But, that is the beauty of cv carbs, it eliminates the need to do so all the time.
It means that they work just like a set of Mikuni carbs with altitude compensaters on them.
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Re: High altitude jetting?

#12

Post by rcmatt007 »

my understanding of the cv carbs was that it was more a way to keep 4 carbs synced by those subtle adjustments than to compensate for altitude. I would also think that the large changes in available oxygen would be beyond the CV changes. Very different than fuel injection in modern engines... but I could be wrong

I just recall that every time I went over the rocky mountains the performance became more anemic the higher I climbed
-Rodger-
all it takes for evil to prosper is the want of a few good men to do nothing-Edmund Burke
The question is not how much time do you have, it is what you do with the time that you have Gandalf
"One of the greatest dignities of humankind is that each successive generation is invested in the welfare of each new generation." Fred Rodgers
"it takes 10,000 hours to become an expert" ancient saying
78 constantly modified/customized since 1978, BOTM June 2015 de-evolving this very moment viewtopic.php?f=30&t=65511
76 Ltd "cookies bike" ALMOST DONE
79 project, finished, FOR SALE
'86 1200 (Beth's)(FOR SALE) with motorvation sidecar (sidecar sold) , July 2017 BOTM
'17 HD Road king and 08 HD Heritage softail (Beth's) (FOR SALE). I guess you can say we have MBS
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