High altitude tuning for 351w / carb?

[conwaj]

I am looking for suggestions on tuning my 351w/carb for high altitude. I am currently running in San Diego (sea level) with about 10 degrees advance (MSD Elect. ig). I am looking at a trip into the Mammoth Lakes, CA area which would put me running in about 8000 to 10000 ft. I assume I should bump the timing up a little (maybe 2 degress?). The carb needs to be leaned? but I am pretty illiterate on the carb adjustments. Any help would be appreciated.

(69 Bronco, 351w, header/duals, 31/2 lift, 6-p cage, 350 gears / posi front and back, still dana30 -8-(, C4, 33 M/T, winch, and 2 Labs -

Thanks

John

 

[FerrumCampitor]

The carb will defintely need to be leaned out. You didn't say what kind of carb, so depending on the brand, you may need to change out the metering rods. And for sure you will have to drop the size of the jets. How far to drop is very hard to predict though until you get to the actual conditions. If its an aftermarket carb (Edelbrock/Holley), my advice would be to buy a tuning kit from Summit Racing that has multiple sets of diffent sized jets (and rods if needed) and tune it once you gt to your destination. If its a stock carb, just buy multiple sets in different sizes getting smaller from where you are now. In CO, once adjusted to run fairly lean at camp, by the time we got to the top of the mountin passes, it was running REALLY rich. So keep that in mind.

 

[Broncobowsher]

I would just leave it alone. So it may run a hair rich at alitutude, but unless you plan to find a drag strip while you are up there it won't matter enough. You risk more damage from running it leaned out at sea level on your trip to the mountains then by running it a tad rich while in the mountains. Save yourself the effort and leave it stock.

 

[COBlu77]

Wait until you get there and turn the idle mixture screws in a 1/4 turn at a time until it starts to stumble and then back them both out 1/4 turn. Write down how many 1/4 turns it took, so you can put it back where it needs to be for sea level. It will definately run like crap, if you don't at least lean out the idle mixture at altitude. Even going from 5800ft to 10000ft makes a big difference with some carbs. Since it's just a temporary thing don't worry about re-jetting, but thats the real solution.