rudedawg

I have a '77 L48 that is a High-Altitude model. After searching, didn't find much info on the specific differences between a Base and High-Altitude L-48. I'm guessing it's jetting in the Quadrajet?? Idle Mixture screws?? Can anyone advise?? I live in Iowa, so I'm wondering if there are any specific baseline settings I should look at checking or adjusting.

gg521

I live in Colorado at high altitude. If nothing has been done to the carb since at high altitude it is under jetted for Iowa. The timing on the engine may also need to be retarded a bit. The other thing is the opening vacuum of the power valve. This may have to be changed. One more thing is the accelerator pump nozzle size.

rudedawg

Thanks for the info. Ironically, my Vette is originally a Colorado car. Last year, I did timing work on it with Lars' papers and got it running much better than it was. I checked my plugs a few days ago and the tips were white. So, I figured the combo of advanced timing and possible leaner carb setup may be an issue going forward.

SteveG75

I would get in touch with Lars. He can probably tell you exactly what changes to make to that carb if necessary.

OldCarBum

We live in the Northern California East Bay Area just east of San Francisco where the ocean’s tidal change actually effects our rivers, elevation 15 feet.
Lake Tahoe, 7100 feet elevation is about a three hour drive from us and we frequently drive up for a day road trip.
The evevation difference with a carburetored vehicle can make in town driving an art.
The Corvette loads up and the idle circuit is definitely too rich.
You should contact Lars and ask him if it’s something you can simply tune out or if there are physical differences in the carburetor’s components and body.