Having trouble with my type 4 bus at high altitude.

[bustedtype2]

So I have a high top 1973 Wild Westerner type 4 with a 1700 and dual 40 carbs. Last summer I drove it to Shaver lake about 5,000 feet above sea level. It started running terrible, not wanting to start and when it did I had to keep the RPM high for it to stay on. When I went down the hill the bus ran great. I have to take the bus to 8,000 feet in a week. Do you think this is a fuel mix fix? Or am I missing something ?
Any help will be much appreciated.
Thank you
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[Angus II]

Hello,
The air is thinner up here... You are running rich, would be my guess. You may have to open up your air mixture screw(s), a bit?, too compensate....
I live at 8,000 ft (+), there is a slight HP loss at this Alt. It just comes with the internal combustion engine. Re-jetting helps if you live up here...

[bustedtype2]

So is this something I should do before the trip or as soon as it starts to run crappy ? At sea level could you tell if the carbs are set at a point that 8,000 would be ok?
Thanks
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[richparker]

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[SGKent]

you are way rich
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Wildthings]

[SGKent]

5000 feet is nothing here in California. If it were 10,000' - 12,000' then it might be quasi-normal behavior but at 5,000' it should run and idle as well as sea level. I don't know how un-synced carbs might mis-behave at altitude. It might make the sync issues almost unbearable, I don't know.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[bustedtype2]

Just drove the bus to work. Yes it’s hella flat in Fresno Ca. The bus runs like a champ! If I was running rich would I be smelling gas or poor MPG?
Thanks to everyone trying to help me.
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[Slip356]

Took my dual carb 356 from WI (1100 ft elevation) to CO two years ago, up to 10 K ft in the mountains. Lost about 15-20% power at high elevations with crappy idle. Was in a group of 15-356’s. Some screwed with the jets, carb adjustments etc.
One guy went to a respected shop in Denver & had jets changed for elevation, dam’n near burned up his motor when came down to lower elevations and switched back to normal jets and then did what I did ‘lived with it’.

[bustedtype2]

Thanks Slip
My bus runs so bad at 5,000 it stalls out. I wish it was just a loss of power. Going to try and lean the carbs. Now which screw is it on the carb? Anyone have a good picture of a Solex 40 carb?
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[Angus II]

Hello,
Slip356, is on to what will happen if you re-jet for high Alt. and then take it back down too low Alt. =(lean).
You would want to do any adjustment up here, then readjust when heading back down.
I know a lot of people used too use an fuel additive (oxydizer) in their race bikes when coming up to the motocross, to get around the re-jetting.
Where are you going, the upper-Yosemite?(Toualame meadows).

[Wildthings]

[bustedtype2]

Going from Fresno to Wishon Dam for a camping trip. Last time I drove to Shaver lake at 6k feet. It was just before Shaver when it started choking and died. It seems like a fine line between adjusting and replacing jets. I may do a practice run to shaver to see how it goes.
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[SGKent]

You are too rich or unsynced. We aren't talking a racing engine here where we are looking for perfect power at 5000 feet and perfect power at sea level. An engine that is properly jetted at Fresno will run fine at 10,000 feet but with a little loss of power. ALL internal combustion engines lose power at altitude because the air gets thinner unless that engine is super charged. I've owned many carbed cars and been at sea level, below sea level like death valley and at 11,000 feet in the Sierras with them. They run fine at all altitudes. If they don't then there is something wrong with the sync or the mixture is too rich. In fact, if you are having this problem, put a sniffer on it in Fresno, sync them, and dial it in properly. You'll pick up power in Fresno and run right in the Sierras. One does not make power by adding more fuel than the oxygen in the air can support. If it is choking at 5,000' then it is choking in Fresno.

There are a couple remote possibilities of other things that could be going on depending when it happened and the circumstances. Just because you were at 5,000 feet doesn't mean 5,000 feet caused it. If it did it at the end of a 5,000 foot climb then the engine would be very hot and if you had tight valves that could cause it. If for example you have something other than factory pushrods using .006" clearance then they could be too tight. Once the engine cooled it would have run right. Another cause can be icing. On the long climb you could have run into carb icing which made it run badly. Once the car sat 10 minutes it would have run fine. Timing way too retarded could cause it because engines need a little more advance as the altitude increases, but that is a really long shot and your timing would need to be way off.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Wildthings]

[bustedtype2]

When this happened it was a summer day and it was at the top of the 4 lane a vary steep grade for about 15 min. So ya at first I thought it was hot. It died and we pushed it off to the side. Waited 5 min and it started but rough. I made it to the lake and fished for 7 hours. The bus had trouble staring and had to rev the engine to get out of the place I was in. As I drove home the lower the altitude the better it ran. When I was on the valley floor it ran like a champ. So I don’t think it was the heat after resting 7 hours.
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[bustedtype2]

The day in question.
Thank you for all your help.
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Gas, Grass or Ass ? No one rides to the show for free!!

[Wildthings]

[SGKent]