Bonneville America Forums Forums Technical Forums Performance Mods Elevation Adjustments

Hey Gang,

Next summer, I'm planning on taking a trip to Estes Park, CO, and the elevation change will be approximately 800 feet to over 7500 feet (and probably higher as I do some additional exploring). What should I expect from my bike in terms of running a little rough... to running a lot rough... to stalling? Will air/fuel mixture screw adjustments suffice when the bike starts to run too rich? Thanks in advance.

Denny, we in Aus don't have the highest mountains but I have travelled from sea level to a ski resort called mount hotham which is 6000 feet. I never had to do anything adjustment wise but I do have thumbscrews if need be.

So unless your bike starts running a bit rough, I wouldn't be concerned about it, and the worst I guess that could happen is the idle running a bit rough and you can sort that out with the thumbscrews.

I suppose if you had your bike tuned to sea level and then you were riding high up into some descent altitude, then perhaps there might be some idling issues.

For instance I live at around 2000 feet, and go down to the coast and have no issues, and likewise have gone up as far as 6k too with no probs. Keep in mind the tuning at 2k will only give a differece of 4k. If I was at sea level and then went to 6k there might be a difference but I don't think so. In fact I've never heard of any circumstance yet where anyone has had to adjust much as they travel from here to there, unless it's a long long way going up and down and round and round etc etc.

So I wouldn't think there was much to be concerned about but perhaps someone else will give their viewpoint from similar experiences so you can ascertain what you may expect.

Many thanks for the great info, Staffo. It's pretty cool to hear from you all the way around the world!

How about others that have gone from the coast or plains up into the high mountains? Did you encounter any issues due to elevation? I learned today that we might get up over 10,000 ft. That would be a difference of over 9,000 ft.

Also...

I've read here that you really shouldn't run with a/f mixture screws turned out beyond 3.5 turns. On the other hand, is there a minimum that the a/f mixture screws should be turned out away from the stop? (In other words, can I ride with the mixture screws turned ALL the way in?) Thanks, again.

I didn't have to change anything when I went to Sturgis in '08, and that area is in the 5500 to 6500 ft above sea level range. I wouldn't mess with the bike if it's running well.

Hi Dave. Thanks for your input. I agree - I won't mess with anything unless it starts to run rough. But if it does, I want to be prepared. (Thus the reason for me asking these questions about eight months in advance )

I wouldn't worry about it but you may notice some loss of power in the highest passes.

Two summers ago I went through some 7000 foot passes and found the bike struggling. I wouldn't call it roughness, it felt and sounded smoother than usual but lacked power. The issue disappeared when I lost some altitude.

You're way down in air pressure by then and presumably it has the same effect as a lower compression ratio. Nothing to worry about but don't drag-race any EFI bikes up hill in the passes.

By the way, I wen't back through the rockies this summer but I guess never quite as high so I didn't experience it.

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I learned today that we might get up over 10,000 ft. That would be a difference of over 9,000 ft.

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Wow! That's getting up there... in aviation 10,000 ft is the ceiling without a pressurized cabin. Would love to be that high on a bike. Oh, and btw... I think the bike will be just fine. Not optimum, but fine. Kinda like people!!

Thanks for the input, guys. It sounds like it's not going to be that big of a deal - which I'm happy to hear.

I did try to convince my wife that I needed to get another bike (with EFI) for the trip. She didn't bite though.

Nah, stay with carbies. They'll be a collectors item one day and anyway, nothing like doing your own fiddling too and the satisfaction with getting it right.

Beats IMHO having to deal with dealers. Not all bad by any stretch but I just like doing my own thing. Feels great and saves $ in the process.

Just my 3 cents worth

staffo

ps: Higher altitude = thinner air = less air I believe = richer mix = not running as well, but least it's not running lean. No real probs running rich but running lean you can burn out valves etc

Can anyone validate I haven't got this wrong. It's just how it looks to me

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ps: Higher altitude = thinner air = less air I believe = richer mix = not running as well, but least it's not running lean. No real probs running rich but running lean you can burn out valves etc

Can anyone validate I haven't got this wrong. It's just how it looks to me

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That's about the way I figure it too. I remember when we drove our fifties and sixties cars through the Rockies and such and a lot of us would pop the hood and mess with the mixture screw just to get 'er to run a bit better at higher elevations. And you're right... rich for the short term wont hurt a thing.

I see nuttink

One rule of thumb is to up/down jet the mains 1 step from baseline for every 3000' elevation change (down for higher, up for lower). That said, I would just ride the bike & live with it unless you plan to be at a particular elevation for a period of time.

thanks for that Ken. I didn't know that but makes good sense and will keep it stored in the jumble at the back of my brain.

I guess that also applies to any changes made to needles and pinses Apologies but it just sort of rolled off the top of my keyboard LOL.

I meant needles and pilot jetses? Now I'm getting worried

That's actually why we have the elevation column in the Dyno Table otherwise it can confuse why people have this jet or that.

Actually, as I do the dyno table if anyone does want to let me know what their elevation is, I'll ammend the table. Just makes it more of an accurate tool that's all.

Sorry to be daft but... to get a richer mixture, one would have to turn the screw clockwise or counter-clockwise?

I got thumbscrews coming up from Eddy and I want to adjust my carbs and set a tad richer because of the hot weather we usually get around here.

In these carbs, out (counter clockwise) = richer.

super! thanks!