liloldfunkydude

Would appreciate your advise. I have a 340 hp 4 speed which drives super, but when starting in 1st gear car hesitates unless more gas is applied. The other 3 gears are fine. The car ran excellent at sea level, but I'm at around 5,500' now. Probably going to take it to a mechanic, but would like to get advise from you all first. Thank You and Merry Christmas.

Save the Wave

MikeM

Take it to a mechanic that know the effects of high altitude on carburetor jetting. That may not be your problem but jets that run well at sea level are too rich at 5500 feet and can cause your problem. Among others.

Crunch527

MikeM is right.

I used to live in colorado springs…7500ft above sea level…you need to tune your carb for elevation, i.e., drop the jet sizes among other things…your carb is too rich and that is contributing to why your car is not running like it did at sea level. Note: at higher elevations, engines make less power…simple fact of barometric pressure or air volume.

I talked to a forum member who lives in colorado and is a very reputable carb tuner on this forum, his name is Lars…knows more than I could ever dream of forgetting about carb tuning. He can help provide some valuable insight. Do a search and you will find his posts.

My recommendation is to send Lars a PM and he can help guide you, before you show up to some random tuning shop who only knows modern efi cars. I have been there and done that. These old cars require "artistry and skill" to tune and adding the complicating aspect of elevation, an expert like Lars can save you hours of frustration and $$$.

He helped me tune a 383 stroker that was pushing 550 horse…I got it as close as I could with the elevation limitations.

Cheers,

Frank

62Jeff

Great advice, but Lars only responds to e-mails now:
V8FastCars@msn.com

liloldfunkydude

Thank you for the advise. I'll email him.

MikeM

PS. Higher elevations vs low elevations usually means you can advance timing or use lower octane gasoline for any given engine combination.

wombvette

Also might check the vac advance. The HP engines tend to stumble off idle, especially when the advance is not correct.

RestoMike

A misfunctioning vacuum advance, wrong advance or one that is not getting full time vacuum will cause a stubble as well.

AZDoug

As Lars says, and he is correct: "90% of "carb" problems are ignition related".

I would suggest analyzing the centrifugal and vac advance mechanisms of your dizzy, along with correct initial timing firs, THEN look at the carb, maybe the accel pump.

My experience with high altitude, over rich conditions, is that you can only run the car in lower gears, they don't like 3rd and 4th gear and will chug.

Doug

warrenmj

I live in Colorado Springs at about 6200' and you need to tune the carb for high altitude as MikeM states. I believe there is an NCRS chapter in Albuquerque and they should be able to help you tune it or direct you to a shop that can do it for you.