Really need this answered before I spend money in the wrong direction.

Gonna replace my Holley back to a Rochester 4MV.

1. As mine is an 1981, I assume it originally had an electric choke ?
Does this matter ? Can I use a manual choke, ? or no choke ( just pump the gas a few times )

2. AS for flow rates and bolt fittings, are all 1972 - 1982 carbs the same - therefore apart from the choke issue, can I use any ??

3. On a street driven car, is there much difference between vacuum and mechanical secondaries - performance wise ??

4. Typically on the street, what milage will a carb do before needing a rebuild ???

5, Any issues I have not covered above that I should know about ??

6. If anyone does have my " perfect carb " sitting home looking for a new place to live - shout !!




5, What is th CFM rating of the stock 4MV ??

 

No carb experts out there ....................
Come on - need help.

 

go to www.corvettefaq.com find Lars Q jet tuning paper. There is a whole cart of all Chevy/pontiac Q-jets so you can compare. although many look similar thaey can be quite different like...80-81's are computer controlled so they are not just Q jet's. Also notice there are many calbration differences. What ever you do stay away from over-the-counter rebuilt units. Your chances of getting one that even runs is about the same as winning the power ball lottery.

 

'81 had electric choke. It also had computer control of the carb - assume yours has had its computer removed?
I'd hook up one with an electric choke as it's only a wire to connect up. No choke isn't a problem for starting (just pump it as you say), but won't the fast idle be inhibited? ie. until the engine warms up it'll just keep stalling at idle (that's what mine was like when I disabled the choke).
Dunno. I do know that a carb from an '80 (not Calif - which was also computer controlled in '80) is an ideal replacement. Probably also '79, '78.... Somebody here would know all the differences (Lars!).
Pass. Vacuum secondaries seem to be easier to set up, etc, at least that's how it seemed to me when helping a mate set up his mechanical secondaries.
Quite a lot I would have thought. Mine has 70 000 on it & just needed adjusting correctly. One thing that was worn, & would be a good upgrade to any Q-jet you buy, is to fit bushes on the throttle shaft. As the shaft rotates in the body of the carb (which is made of monkey-metal) it wears an oval. The return spring placing a load on the d. side doesn't help here. Once worn you'll get a small air leak, but more annoying is that the throttle blades will rarely shut correctly. You'll come to a halt to find the idle speed is totally random. Just really annoying, especially if you've spent ages setting up a really nice, smooth, even idle at 600rpm & then blip the throttle & find the idle goes up to 800rpm. The wobble on the shaft probably doesn't help with the idle/off idle mixture. It's an easy job to fit the bushes. If you don't want to buy the entire kit, you can just buy the bushes (or get some made - there's nothing to them) & I can lend you the reamers.
A deafening silence from over here....

If you're going with a Q-jet then it's definitely worth getting a book by Doug Roe on them. Excellent book with a lot of improvement mods.