What is the limit on jet size on the center carb and also meter plates on the outboards for vacuum secondaries? They can only flow so much right?

I have one set of early (1970) OEM carbs that have been modified to use screw in air bleeds on the outboard carbs. metering plates, choke plate removed on the center carb, still vacume operated. I have had 68 jets in the center carb. with a 4.5 power valve and a .035 power valve restriction channel, the outboard carbs. have had .092 diameter holes in the drivers side and .096 in the passenger side and ran the fastst in my car. I switchd to .096 on the divers side and .102 on the pass. side and slowed the car down. I want to try .094 on the drivers side and .098 on the passenger side next I have not ran it leaner than that, The wideban showed 11.8 to 12.3 with the bigger jets and 12.8 to 13.3 with the smaller jets, both times using Oregon 92 octane pump gas IHTHs

If you are serious about tuning your six pack, do yourself a favor and buy 'jettable' metering plates from Promax, etc as well as a new base plate from them for the rear carb which has the mixture screws at a 45'. Then they can be adjusted with the engine running. Also there is some good info here in the tech archives.

Outboard jet plates will allow you to better tune for wide-open throttle without compromising the idle and cruising circuits of the center carb.

I found the promax site And see the pieces you posted to install thanks.

I went to the indy swap meet today and stopped by promax and bought their jet plates. They had suggested #78 jets in the front carb and #84 jets in the rear, with a #64 in the center and a 3.5 power valve and yellow springs in the diaphrams.


Just curious as to why 78 in front and 84 in the rear instead of the same size jets in them both? I am planning on trying it, but going to use the track at test n tune to see the difference.


This is a 70 barracuda street car 499 build on a 400 block with fully ported 906 heads 214/181 valves, shaved around 80 thou and a lunati solid 583 lift cam installed at 106 center, 4 speed and 410 dana.

Im trying to build this to beat up a machinst friend of mines 69 chevelle 454. He went an 8.23 in the 1/8 mile and said he doubted I would take him. I think im there now tho, but have bought some 315 60 15 et streets, a doc diff 1 inch offset kit and lighted the front end by 100 lbs. Also installing a set of 2x3.5 hookers and 3 inch exhaust. Seems an 11/1 or so comp 499 and jetted right should smoke this guy. It's mostly chevies around here so I need to stand up and be noticed some. Any suggestions would be helpfull, I have a few weeks left before I try the car out.

If you can get that beast to hook you wont have any problem running that fast, in fact if you can get the launch down I would guess your car to run mid 7s based on your combo.

im running 64 center, 84 front and back with the promax plates.

with crappy tuning, and cherry bomb mufflers hanging off the headers (i think they were 1 1/2" diameter thru the muffs), i ran 8.1 in the 1/8th about a year ago with my 416. cam was smaller than yours, compression about 9.7:1, 4.30 gear, 275/60/15 tires.

i havent been to the track since i changed the exhaust to 3" and changed a few other things.