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Discussion Starter #1
Hello from the other side of the ocean.

After a long time I’m back here in this forum. The last year the Nova has become some changes.

Replace the rear end with Differential from 2.56 to 3.08, new Motor mounts, change from 14” to15” Rally Wheels in the back with 245/60, rebuild the leaking cooler, mount new trottle shaft bushings, mount a three point safety belt at the back seat for the children’s seat of my son, electrical fan,…..


And now I’m asking one question about my Q Jet.

At my 69 Nova with 307 / TH350, mild cam, 305 Heads with smaller cambers and a compression about 9.6: 1, dual plane intake, Hughes torque converter with stall speed 2000-2200, and a Chevy Q Jet form 79, headers with dual exhaust.

This works are done:
Timing 34°@3000 and 12° at idle without vacuum, HEI with new parts, new throttle shaft bushings, no vacuum leaks, new base gasket, 3.0 – 3.3 % CO at idle, Lambda 0.83-0.85 under full load, choke is totally open when hot, the fast idle cam do not touch anything, no drilled throttle blades, first and second throttle blades and air valve are completely closed, idle screw is turned completely back, it starts good when cold and warm and it runs great without sputter from idle to 5000, right ATF level, no slipping from transmission.


I’m wish to turn the idle down to 550-600 in D and give about 3-4° more initial timing. I think it can handle it. But I can’t screw the idle deeper then 700 in D (no load from fan).

In N it’s about 800 and for my feeling it’s to high.

In my two books about Q Jet’s the only have solutions to bring the idle up.

So have I a chance to become a deeper idle or are the idle By-Pass bores in this carburetor to big for my 307?


Hope you understand and please excuse my school English.


Many thanks


Greetings from Switzerland
 

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Put a vacuum gauge on it and check your manifold vacuum at idle. Try adjusting your idle mixture screws (equal number of turns) until you get the highest steady vacuum. You may have to break out the plugs on the carb base covering the screws.

I would recommend you first turn them in (with the engine off), counting the number of turns until lightly seated. Write down this number in your tuning notebook, then turn the them back, with both an equal number. This will give you a reference baseline you can go back to if it gets worse. If they were not the same, then make them both the higher number of turns.

If the idle vacuum is still low after adjusting idle mixture, you may have a vacuum leak at the base gasket. The '77-'79 Quadrajets take a special thick gasket with phenolic bushings that limit gasket compression. There's a real good chance the one you have isn't sealing right. Don't over torque the bolts to try and seal it. You have to replace it with a new one. There are several versions so you need the one that fits your base. I'll try to find the gasket only PN, but the correct gasket comes in the Delco carb kit GM PN (Gr. 3.725) 17076038. You should be able to order it from your GM dealers in Switzerland.
 

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Discussion Starter #4
O.k. Paul thank you for your ideas.

Two years ago I have change the intake and I remember there was a thick gasket like you talk about. At this time I have use a thin paper gasket under the Carburetor. So I look for a thicker the next days.

The other point with the vakuum. I have only a pressure/vakuum gauge out of the dash of my old Saab turbo. Next week my holidays are over. Then I can look about the vakuum at work. There I can also use a exhaust gas analyzer. Don't won't the engine runn's to lean.

Btw: here in Switzerland it's nearly impossible to get parts for old cars from the GM Dealer. This Dealer are only for newer cars and parts. The rest is from specialists they only deal with old parts or new parts for old cars. Or direktly from USA with a handling,tax and shipping the parts ar about three time more in price.

But anyway thanks for the part numbers.

Many thanks


Greetings from Switzerland
 
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