I've searched the net and can't seem to find what I need. Most sites talk about metering rods, float adjustments etc. Not that these aren't important, but I'm just trying to do some basic tuning. Original carb so not concerned about rods at this time.

I need to know the answer to some of these questions. And as always, advanced thanks for the help.

What rpm's should the high speed idle adjustment be?

Should the choke close all the way when starting cold engine? If not, what should the gap be?

There is a gasket on the choke housing. How important is this gasket? Mine is cracked.

If the chock isn't coming off fully, thus allowing the secondaries to open. What adjustment do I make and where do I make the adjustment?

 

Since I don't have a '76 (or manuals for them), I can't provide those details. But I will say that all of that info is in the Chevrolet Chassis Service Manual in the "Fuel System" section. You really need that manual, if you don't already own one.

The "Hi idle" speed should be listed on your emission sticker [left-top firewall] and is usually around 1000-1200 rpm; no, the choke plate does not close down completely; the gasket is important, in that it seals heat into the spring coil so that it will expand and it prevents hot gas from being released next to the carb...make one out of paper gasket material of use some hi-temp sealant; there are several choke adjustments to make and all need to be correct for carb to work as designed.

 

I would recommend getting Cliff Ruggles Q-Jet book first and doing some reading about the hows and whys on these carbs, as well as Lars postings here on this forum (these guys are a wealth of information) then if you have any other questions or need parts or advice you can contact Cliff the author directly or post your questions on his Q-Jet forum:
http://cliffshighperformance.com/
I just went through a Q-Jet on a 72 and learned alot about it's operation and what modifications or repairs to make to correct a specific problem. I started with a car that ran horribly, no throttle response and wouldn't idle at all and went through everything step-by-step and in a couple of weeks of tweaking this and that; I now have the car running perfectly! You could also just send Cliff or Sean Murphy (smicarburetor.com) your carb for a complete overhaul first to make sure everything is in order and to give you a good baseline or do it yourself using the book as a guide.

 

Cliff's High Performance | 20579 Berry Road, Mount Vernon, OH 43050 740.397.2921

I suggest you ask him about converting to electric choke. Simple and works better under a lot of varied weather conditions.

 

1. Spec is 1250, but I find this to be a bit high. Set it to 1100 and you'll be good.

2. Yes, the choke should snap fully closed when you crack the throttle open on a cold, non-running engine. Upon start, the choke pulloff should open the choke 1/4" as measured from the lower forward edge of the choke plate to the airhorn wall. Measure this with a 1/4" drill.

3. The choke housing is exposed to a slight vacuum source, which draws air from the upper, rear fitting of the carb, through the hot air coil in the manifold, and into the choke housing. If the gasket is leaking, you will get cold air dilution with the hot air in the choke housing and your choke may never fully open. Replace the gasket. The only time you want to eliminate the gasket is if you install an electric choke conversion - the electric choke will not ground or operate if you have a gasket installed. But for hot air choke to work, the gasket must be intact.

4. The choke should be adjusted so that the line on the choke cover aligns with the casting reference marks 2 notches clockwise from the center mark. If the choke is not opening fully, thus not retracting the secondary lockout lever, you either have a faulty choke coil or you have a cold air leak into the choke housing. You may also have a restricted or blocked manifoild exhaust crossover if the choke housing is not getting hot enough.

These adjustments are covered in detail in my Q-Jet paper, which has been available to Forum Members by e-mail request for several years.

Lars
V8FastCars@msn.com

 

Didn't you mean:
If the gasket is leaking, you will get cold air dilution with the hot air in the choke housiung and your choke may never fully open

 

Thanks for pointing out the typo. I have edited the correction into my post above.
Lars