Hey guys,

I have a 69 RS Z. It is stock except for headers and electronic ignition. When I bought it it had the wrong carb. It was a 780 duel line that had been reworked with opened air bleeds and 76 jets in the front and 83's in the back. Ran really rich but ran OK. I bought a correct 4053 for it. Looks real good and clean, with no apparent modifications - even had the goop still in the air bleed adjustment holes. Did appear the jets had been changed. I have a friend who owns a auto parts store and has access to old books and his holley book said it should have 66 jets in the front and 72's in the rear. I put those in during the rebuild and it idles fine and is no longer rich at idle. Now under load it pops and cracks and even dies. I am thinking maybe the jets are wrong. What do you folks think? What jets are you all running in your carbs?

Ed :confused:

Welcome to TC Ed,

Jetting should have no impact at idle so your rebuild gets the credit for restoring proper settings of the idle circuit of your carb. My Chassis Service manual shows 68's and 76's from the factory.

Try a hotter plug. If you are using the AC R43's you will probably get fouling while driving around on the street. I have had that happen and cause afterfiring in the exhaust pipes. Switched to R45S plugs and the problem went away.

Just another thing to consider.

-Mark.

I have a stock 68 Z28. Stock, factory original everything. I run 72 in front and 76 in rear. Works good.

Stock jetting is 68/76. Mine ran lean with 66 primary jets too. Common jetting for these motors is 72/76. After a full day of dyno testing with air-fuel ratio monitoring, mine made the most power with 70 primary and 66 secondary jetting. I was really rich on the top end with the stock 76 secondary jetting. My engine has aftermarket aluminum heads, so results may vary.

I am running 72/76's and the car runs great. Stock 302, cam, distributor, carburetor with hooker headers through factory exhaust.

Neil How much power?
Dan B

Dan B,

On the chassis dyno, it made 283 hp at 6,000 rpm and 278 lb ft. at 4,000 rpm (SAE Net).