Elevation changes affect on carb settings
 

I bought a LeMans off of a guy in Colorado last year. The Quadrajet is due for an overhaul. I’m in Wisconsin, about 7500’ lower in elevation. Hypothetically, would an elevation change this big warrant jet, metering rod, or spring changes to lean it out? I figured as long as I have the carb off, now is the time.
Thanks

A drop in elevation means you have dencer air and that would require richer jetting assuming that the Carb was jetted right for that higher altitude it Cam from.

Absolutely makes a difference. I deal with it all the time living at elevation and frequently driving to sea level.

Like Steve said really depends on how the carb was set up to begin with. It may have just been running a bit on the rich side up there.

Just have to try it out and see. If you're rebuilding anyway may as well get the kit from Cliff and he'll spec the parts for your combo, then you won't have to worry about whether it's been tuned previously.

So, i recall a story about people with Carb'd cars running outta Gas along a high-altitude HWY out there due to low-altitude settings and thinking they will get the typical MPG at such high altitude. Good case for O2 sensors or...Fuel Inj.

I've never run out of gas living at the higher altitude and to be honest there isn't a huge mpg difference I've calculated from driving up here or at sea level.

Basically if it helps others to put a number on it, from what I've seen on the AFR gauge at 6000 feet vs sea level is about 1 point in AFR.

So I generally tune the carbed cars to be a pinch rich up here and they daily drive just fine like that, then when I drive down to sea level they are still in a happy spot. What you absolutely don't want to do is lean it out up here and then drive down to sea level where it'll lean out more on it's own and put the engine in a dangerous spot.

For instance the daily drivers cruise around upper 12's to low 13's AFR when we are a mile up. That leans out to upper 13's at sea level. Basically I just live with them being a little fat at elevation and that works just fine, doesn't really affect gas mileage and the plugs stay clean.

Ideally EFI that has close loop compensation has an advantage in this scenario as it will keep the AFR you want no matter what atmosphere your in. We did switch 2 other cars over to EFI for that reason, and I'll admit it's pretty sweet.

I'm still recovering from a frustrating mess, aka Frankencarb, and don't wish it on anyone. Good clues for history of a "factory rebuild" are stripped finish and/or a bar across the vent hole as attached. A rebuilder sticker is an obvious indicator. I sent it to shaker455 after fighting it and he worked wonders.

Go through the carb before calling Cliff and make sure the carb has its original parts (body, airhorn, base). This alone can be a challenge as the part numbers in online references are not labeled on the parts. If you have any doubt, post photos and ask those that have seen a few hundred of them!

Then measure everything and compare with stock. Cliff can't tell what you're starting with. Informed decisions are better than assumptions.

It is hard to find the original configuration (DCR, airbleeds, bypass, etc.) to know if they've been modified. Kenth gave me a lot of that info and I was grateful.

Thanks guys. I just sent Cliff pics and info last night.

What ever might be in the carb really doesn't matter much when you're at the point of going through it anyway. You'll be changing the airbleeds, bypass air and IFR's anyway because the stock configurations aren't much use today.
Cliff will supply you with all that stuff.

I had rejetted the stock carb on my 78 TA with an HO Racing kit living in San Jose. Drove up to Tahoe man it was not happy! Especially in the 30 degree weather.

Just sharing my experience, which included 3 rebuilds with Cliff's excellent guidance, his kits, and several parts.

67drake is way ahead by sharing photos of his carb with Cliff.

In my case, I assumed my carb had the correct parts. They all fit together just fine. I also assumed it had bypass air because the baseplate had those features.

What I failed to do was verify the body had the right features for bypass air. It did not. Nobody could have known that except me and the rebuilder that put the wrong baseplate on that body. I missed it until I discovered the wrong baseplate was on my carb and then took the time to verify.

An expert like Cliff could have seen a photo and recognized my carb had the wrong baseplate. Turns out the "correct" baseplate for my carb did NOT have bypass air, but even then, there's no way to know if it had been added or not without verifying. I failed to verify the first two times I rebuilt the carb. Was it me, sure... am I inexperienced, yes. Was it easy to figure out... not for me.


IMO, there's no way to tell what's already been done without looking and measuring. Cliff can definitely guide on what is needed but if, for example, he knows the airbleeds were drilled out too big, it might affect his recommendations for idle tubes or DCRs.

Mike

I assume you're not aware air bleeds can and usually are replaced to meet a certain goal?? If you tell Cliff what you're doing he can supply the correct airbleeds, idle tubes etc.... and calibrate the carb correctly. That was the gist of my first statement of why it doesn't really matter what's been done previously, because I'm usually going in with the mindset I'll be changing most everything anyway to fit the engine it's going on. I wasn't really speaking of a generic rebuild where the carb is just taken apart for gaskets and a new squirter.

On the other hand, when we who live up near Tahoe/Reno drive our carbureted cars down to Sacramento and the Bay Area, wow do they come to life! Too bad they don’t sell THAT in a bottle.


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Yep. It's easy to get complacent with the car at high elevation only to have it surprise you when you jump on the gas at sea level.

Just for giggles if anyone wants to put numbers to it, you lose roughly about 3% power for every 1000 feet in elevation.

So a typical 500hp street car at sea level will only make about 425hp at 5000 feet elevation.

Hence the reason correction factors exist.