What Weber main jets for high elevations

Just wondering what size main jets folks at 3,000' or higher elevation are using?

Also wondering if some of you change main jets going from a low elevation to a high one or do you just choose some average sized jet number and go with it.

At 1,600' my engine is happy with 125s and at 600' it likes 135s.

I would suggest asking Jake as he knows your motor and carb combo. .... ~Alan

In the early days of EPA testing, this presented a problem for Porsche. They were told that if they wanted to sell a car at a dealership whos altitude was 5,000 feet or above, they had to have the car certified not only in Ann Arbor Michigan but in Denver Colorado as well. This initially presented a problem which required a change of jets just prior to the car being transported to Colorado from Michigan.

This also presented a problem for me when I would drive these cars from Colorado back to Calif. Once I got to St. George Utah, I'd have to change jets in those triple Webers. The early mechanical injection required a lot of equipment to adjust the mixture so they said do nothing until I got back to California, the would then re-adjust the mixture and richen up the fuel delivery. Finally, in 1973, they switched to CIS injection and although it was fuel Injection, it was crude. I would have to richen up the mixture by placing a 3mm allen wrence into the fuel injection distributor and adjust the mixture by sound.

Later, when an 02 sensor was added no adjustments were needed.

I know a few people that live in Big Bear (Elevation 6,700 feet) They have hot rods and when they come down to the valley with these cars, Many of them just switch carburetors as it's much easier to change carb's than the jets

I was told to change the air correction jets (the ones on the top of the central tube in the throat) when I went to Denver and above. That would have been on my old '56 1600 normal. A small screw driver and five minutes was all it took. I guess it made a differnce, but was hard to tell. Just don't drop 'em down the hole, then five minutes turns into five weeks, if your lucky.

When I picked the Speedster up at Jake's he had 125s for main jets---his elevation was 1,600' He said to change to 135s when I got home to Hot Springs which is 550'. I did make the switch and felt the engine ran better.

For the Morro Bay trip I'll leave Hot Springs (550') go through Amarillo (2,500' or so) on to areas of 3,000+ feet and into Morro Bay at 800" (guessing). Point is, should I start out with the 135s leaving Hot Springs and plan to change to a amaller jet as I get higher with thinner air or just put in maybe 120s and do the whole trip with that size? Or change as I go higher? It only takes 2 minutes to swap 'em out.

Too bad our carbs don't have a mixture control like my Cessna Cutlass.

What do others do when driving into different altitudes?

Sure I'll check in with Jake which is something he strongly encourages but I wanter to see what othere here do.

Do others make any carb adjustments other than the carbs?

FWIW - We took our 1995 VS (1835cc/dual Kadron) that lives on the SoCal coast at sea level, on a trip to visit Dusty & Sharon, drove through Moab (Utah) at 4,100ft and in the Colorado Rockies at 9,000+ without a single hiccup. Is it really necessary to re-jet?

They have Webers

I'm just saying...

Jack, Leave the carb jets alone. It's not worth the time to change the jets considering the short time you'll be at altitude.

Think about it. Back in the days of carb's. Millions of people drove from the east coast to the west coast and, from the west coast to the east coast without changing jets.

I attended a 356 registry at the Stanley Hotel in Estus Park, Colorado, back in the 80's. Part of the deal was to go up Trail Ridge Parkway as a group.

Some had problems and some had less problems, but everyone felt the effects of altitude.

Fuel injection helps, a lot.

Turbo equalizes?

But altitude always wins in the end; like a vacuum.

Just my two cents. I sleep at 7k feet above sea level.

" I sleep at 7k feet above sea level. "

Better than 6 feet under...;)

I go from sea level to 3600 ft. with out any noticable problems....I jet rich just to keep the heads cool....Still get 32+ mpg. ont the hwy.

Think about it just a bit. At sea level or close you have the most air pressure v fuel you will have with your jetting. At higher elevations you will be too rich which is not as bad as the other way around. Know you will be running rich and don't let the car idle too long and foul plugs. Other than that you should not have any problems. If anything leaving the jets alone and changing the air correctors if your running Webers might be the only thing I would do. Bigger air correctors would compensate for a rich condition on your mains but not do much for the idle circut.

Without electronics and O2 sensors it would be tough to know for sure........;-)

I'm hoping I make it to SLO to see Jake's creation.......

Thanks, Dave. I believe I will go with 130 mains and that's that. I'll carry spares along if it becomes an issue. I just think too much of this engine to not make every effort to make it as aappy as I am with it!

Yes, I had Solex/Kadrons before and they were great. I was at the Tail of the Dragon twice with the Kadrons and there was never an issue of pinging or loss of power --all over the Smokey Mountains.

---Just thought I'd ask.

I'm late to the party, but I'll put in a vote for leaving well-enough alone. Remember, I live at sea level, but we get above 5000' on the Cherahola Skyway. I never noticed any mixture issues.

Have you never seen a dual carb engine idle at 250 RPM? I have, while parked in front of a sign stating, "Continental Divide, 10,000 feet elevation"!

I wouldna believed it if I hadn't seen it!

Jack,
On the trip I'll be available for a phone call. You can give me some data from the instruments and I'll help you with jetting.

Thanks, Jake.