[AJD1964]

In the near future, I plan on using a '70 cast iron 4bbl intake with a '70 Q-Jet (7040264) on a low compression 350/TH350, and will be getting rid of an Edlebrock performer set-up, and unknown cam. The car is a 1971 Lemans.

On the Q-Jet, there is a 2nd port on the choke pull-off vacuum diaphragm, which according to the '70 shop manual, connects to a vacuum canister ball on the right fender. Problem is - the car is a '71 and does not have the vacuum canister "ball".

Question - Can I just block off the extra vacuum port on the diaphragm for this and ignore it? If so, will I have any issues with the choke on warm up? It'll be a while before I get to actually testing this, just doing research at this point. I suppose I could add it, if necessary.

[Blued and Painted]

Yes, cap off the extra port.
The amount of choke pull-off is mechanically limited and wont change.

[Schurkey]

But it will actuate faster.

This is not likely to be a problem, since 99% of choke pulloffs DON'T have the extra volume of air in the vacuum ball to contend with.

Apparently, GM wanted the choke pulloff on those vehicles to work very slowly. You'd just be going back to "normal".

[Blued and Painted]

Then there is the secondary top flap braking function. Opening time is critical to secondary function. Pull-off tuning/timing is outlined in Cliffs q-jet book.

Call cliff with carb number in hand and get your autographed copy coming.

http://www.cliffshighperformance.com/

[AJD1964]

Blued & Schurkey - Thanks for the tips.

I do have Cliff's book. I should probably call him to get a better "calibrated" kit for running a 350. The Q-Jet looks and seems to be in really good shape, but it's probably still originally calibrated for a basic 400 GTO motor from '70, and may not run as good on original low compression (8.0:1) '71 350 heads as it should?. I will be using 3.23 open gears.

On the cam - I'm stuck on deciding whether I should go with the stock "066" or the Summit 2800. I don't think the lower compression will like an "068", which I have in my '64 389, which I really like in that motor.

[moontower69]

Originally Posted by AJD1964

On the cam - I'm stuck on deciding whether I should go with the stock "066" or the Summit 2800. I don't think the lower compression will like an "068", which I have in my '64 389, which I really like in that motor.

I'd go with the Summit 2800 cam for a low comp 354. It has more lift and faster ramps (less advertised duration) than the 066. [204/214 & 262/272 adv. v. 200/210 & 273/282 adv.] I have the same dilemma in changing the stock cam on a 354 refitted with 4X heads (7.6:1 at best). I've been told on this forum that for me, the Summit 2800 will have a little more torque down low and a bit more on the top end than the 066. With the right heads to get the old 354 to 8.5:1 or 9:1, then I'd go with the 068 and advance it 4 degrees for more low end.