Rejetting for mountain pass tour

[zenithblue71T]

Guys, I’m planning on the once in a lifetime run through 7 passes in the Alps in August 2021. Given my experience at Lassen volcanic park in NorCal, I will have to rejet my carbs to not get bogged down to 40mph max speed. What should I re-jet to? I will be on about 99 octane pump gas. I have to drive 12 hours to get to the pass through the fatherland. I will have to rejet between 12 hour drive and mountain pass and once again to get home. My current setup is I believe:

40Mm PMO
Main jets .125
Air correction 1.80
F16 emulsion tunes
Idle jets 0.55
32 Venturis

If I go up elevation, should I lean it out? What should I rejet current setup to in your experience?

[Xavier PJB]

I did 14 Alps passes in 4 days in 2019 with my 911L 2.0 Weber 40IDS tuned for Paris altitude - the only issue I had was with the ignition points.
I did not rejet anything and used my standard setup and I enjoyed it a lot !

[zenithblue71T]

Ok, do you by chance know your carb specs Xavier? Do you have hot cams?
I have hot solex cams, 2.2S and single plug. Mine was a dog at 3100 m2 or 10,000 feet.

Also, do you want to join us? We depart Zurich on 6 August.
https://www.classictours.dk/joyrides...ountain-passes

[Spyerx]

I run my 71 tuned for beach altitude up over 7k feet in mountains around SoCal. It’s grumpy over 4K. Have to pull hand throttle a bit to idle and the throttle is best as an on off switch. Floor it and it’s good.

That motor is out of the car and a 2.8 l efi motor going in next week.

[Richy]

Your car will be down on power regardless , but i would put in a 1.20 main jet so it will not be running so rich . My brother lives in Mammoth Lakes , Ca. at 7,000 ft. and my car is ok but not on Tioga Pass to Yosemite { 10,000 ft } . And do not use high octane fuel , not needed at high altitude , slower burning and even less power . I'm envious of your drive .

[Xavier PJB]

Need to find the details, but it is a standard 2.0S engine 1968 running factory tuned Weber 40IDS - MDS ignition though.

I passed Col de l'Iseran with no issue at all. I run 98 RON fuel, no additive. No overheating, no significant power loss, just pure pleasure.

I would have loved to join you, but am at the west sea coast until end of August working and sailing. Enjoy though !

Old Gotthardpass is a must (did it 7 times)

Ok, do you by chance know your carb specs Xavier? Do you have hot cams?
I have hot solex cams, 2.2S and single plug. Mine was a dog at 3100 m2 or 10,000 feet.

Also, do you want to join us? We depart Zurich on 6 August.
https://www.classictours.dk/joyrides...ountain-passes

[uai]

Just calculate: in copenhagen you're basically at sea level
0 m 100 % 1013,25 hPa
100 m 98,7 % 1000 hPa
200 m 97,5 % 988 hPa
300 m 96,2 % 975 hPa
400 m 95,0 % 962 hPa
500 m 93,8 % 950 hPa
600 m 92,6 % 938 hPa
700 m 91,4 % 926 hPa
800 m 90,2 % 914 hPa
900 m 89,1 % 903 hPa
1000 m 88,0 % 891 hPa
1500 m 82,5 % 836 hPa
2000 m 77,4 % 784 hPa
2241 m 75 % 759,9... hPa
2500 m 72,5 % 735 hPa
2962 m Zugspitze 68,4 % 693 hPa
3000 m 68,0 % 689 hPa
3500 m 63,8 % 646 hPa
3798 m Großglockner 61,4 % 623 hPa

I'd aim for 1000m as the standard once you're in Switzerland so reduce main and idle by factor 0.1 and you're set. Or just drive and have a set of spare plugs with you.
I didn't change jetting from my 550m standard and the only one suffering from my CO was some guy in an aubergine targa being stuck in a traffic jam behind me (Cheers Frederik)

[frederik]

And all the other guys behind me

[Xavier PJB]

Weather, outside temperature is a point to take into consideration also I wonder. I did my passes under pretty cold outside temp.

[Chris Pomares]

What altitude on average are the passes you'll be going over. I suspect there is some math involved to get the correct jetting as pointed out above.
Fortunately I run EFI as 5000 feet is the equivalent of Sea Level here in Colorado. I spend most of the time at 7 to 12,500 feet. I have 3 programs. 0 to 6000, 5 to 10,000, and 9 to 12,500. A run up Mt Evans or Pikes Peak is higher yet (14000). 3 to 5 minutes and a few taps on the keyboard on the side of the road and I'm good to go.
If I can't get it just right I call my tuner. ECU to laptop, laptop to phone and the program is altered when he is 1000 miles away. No smell no muss no fuss. Sometimes in certain circumstances the all original experience out on the road is, well.........