So I bought a carburetor off eBay for my 71 Cutlass, it’s 7041250 so it’s the correct carb, I had it rebuilt but I can’t seem to get it to stay idling under 1200-1500 rpm, also the vacuum port on the driver side on the main body has vacuum all the time and I thought it is supposed to be ported vacuum, currently the engine is not in the car but on a run in stand

 

What year, model, engine and is it in stock form? this problem exist before changing the carb?

Symptoms of a vacuum leak or throttle plates hanging open. Does the choke open completely? Look on the pass side on the middle of the carb for the high idle cam, is it sticking?

Good luck!!!

 

Sounds like the throttle blades are open too far exposing the vacuum port to manifold vacuum. Turn the carb upside down and compare to picture. Are the mixture screws responding? What is the timing at idle with distributor plugged? Maybe post a picture of engine, there are some keen eyes on this site.

 

1971 350 Oldsmobile that was just rebuilt, not a stock engine, flat top pistons, bigger valves and comp XE268H cam

 

When the throttle plates close all the way down where the car should idle the engine dies and the choke is fully open, the initial timing is 12 degrees advance when it does stay running

 

What distributor are you using?

 

Stock GM HEI

 

You need to bump your timing up to 16*

 

Agreed. Higher initial advance will help the engine run smoother and give higher idle vacuum. Plus the HEI doesn't have as much mechanical advance as the points distributor, so the initial needs to be set higher to get the same total advance.


I initially had a Moroso HEI advance curve kit in the distributor and it mimicked the points curve with 24º mechanical advance so I set the initial to 12º. After the cam change I started playing around with the curve again to get a better idle and not drop RPM when the AC turned on. I found that the factory center bar and weights that had 18º mechanical advance worked better, so I set the initial to 18º to get the same 36º total advance. The higher initial gave smoother vacuum and the RPM didn't drop nearly as much when shifting into gear or turning the AC on.

 

Did get the engine idling, initial timing is currently set at 21 degrees I’m thinking I may need to change the jets in the carburetor, doesn’t have the throttle response , maybe a little lean? Engine is still on run in stand

 

Be careful with your vacuum advance, if its not limited to around 10* your going to get detonation at light throttle acceleration.

 

How do I limit my vacuum advance to 10 degrees? I have purchased a new adjustable vacuum advance

 

You can limit the vac advance w a mechanical stop in the distributor or msd etc sell a little part to do the same thing

heres an adjustable one from crane, it may take some mods to work w you dizzy

https://www.ebay.com/itm/Crane-Cams-...UAAOSw51xeoxl1

 

I made my own adjustable stop based on info that was posted online:

https://classicoldsmobile.com/forums...ttings-121195/
https://classicoldsmobile.com/forums...timing-139998/