LowOlds

Hello All,
New to this site and in need of help for my daily driver 1975 Delta 88 Royale 350ci 2Dr convertible.
The qjet was replaced w/670 Holley 4bbl street avenger (nothing was wrong w/qjet, I thought I was improving performance), but have had a difficult time trying to tune the carb. Unfortunately (for me) I cannot diy as I'm out of my comfort zone and patience, also trying to find a mechanic to adjust the carb to my car has been impossible. Any feedback will be greatly appreciated and Thank you in advance.
Will upload photos

oldcutlass

Need a bit more info besides a description that basically says its broke. The Holley carb is a square bore vs your spread bore Qjet. Did you change the intake manifold or are you using an adapter? What are the actual symptoms of your problem?

redoldsman

Good point Eric. I bet he has a big vacuum leak at the base of the carb. Just guessing.

olds 307 and 403

Put the Qjet back on and add dual exhaust if possible, depends on your emission laws. That will restore your mileage and add a bit of power. A stock 455 is the best medicine for your car. No matter what you bolt on a 8 to 1 smog 350, nothing will dramatically improve performance. A full rebuild with bowl work on the heads and flat top pistons in your 350 with a mild cam upgrade is the other option.

joe_padavano

And, you didn't.

First, you have a heavy car with low (numerical) rear gears, and a low-compression smog-choked single exhaust motor. Vehicle performance requires all elements to work together. Simply changing one thing usually make it worse.

Put the Qjet back on. Run a true dual exhaust. Think about a rear gear ratio change. Be sure the ignition and carb are properly adjusted to stock specs. You'll be amazed. THEN start making incremental improvements.

BangScreech4-4-2

The Street Avenger is a great carburetor, but as noted above is a square-bore design. Depending on your plenum design it may not be compatible with a spread-bore manifold. Also 670 cfm is a little large on an unmodified low-compression 350. 570 may have been a better choice.


Regardless, I'm with the others. If there was nothing wrong with the Q-jet in the first place, put it back on.

LowOlds

Thanks for the info/help every bit helps, I'm looking into getting another Qjet.

LowOlds

Hello, you're absolutely right about the vacuum leak. Issue resolved but carb still dumping more fuel into the engine. Work in Progress, Thanks for your reply.

lshlsh2

Welcome, where in Delaware are you? I live on the Eastern Shore of Md. near Easton.