b.jarrell

I have a 1971 Corvette Stingray and I'm having issues with my Rochester 4mv secondaries not opening constantly. Sometime they open fine while other times i have to pump the gas pedal a few times before they will open.

Any thoughts or ideas as to what could be causing this?

oldalaskaman

low vacuum?

b.jarrell

Thanks for the reply.

Here my common scenario, I'm driving down the highway and I'll push on the gas and the secondaries will open properly, like normal. Two minutes later, I'll push the accelerator again and they wont open until I hit the gas a few more times.

Could that still be low vacuum even though it works sometimes and not other times?

lars

Vacuum has nothing to do with Q-Jet secondary operation. The secondaries are mechanical, so if they are not opening, you have a mechanical issue. The only mechanical issue that can prevent them from opening is the choke not staying fully open, thus not allowing the secondary lockout lever to fully retract. For a complete description of secondary operation, along with all issues and troubleshooting for secondary operation, just drop me an e-mail request for my "Q-Jet Tuning" paper - it has an entire section devoted to how the secondaries work, and how to troubleshoot non-working secondaries.

Lars
V8FastCars@msn.com

oldalaskaman

http://www.arkansaspontiacs.org/tech...ockyQ-jets.htm
interesting reading

Mooser

Get those papers from Lars

My secondaries were hit and miss also (more miss than hit actually)

With the help of Lars and his papers and a few forum questions and answers, found that the shaft holding the air-flaps was bent which made it bind slightly in the middle and the flaps were also touching the front of the wall and would stick there.

If you move them by hand, do they stick even a little before the open or move freely?
Mooser

lars

Generally correct, but downright incorrect in the statement, "The secondary side of a Quadrajet is vacuum operated..."

Q-Jet secondaries are not vacuum operated. Complete, correct, description outlined in my paper.

Lars

oldalaskaman

excellent , thanks for the input

RedZR

One other really low buck thing- check to make sure your floor mat is not preventing your gas petal from going all the way down. I was having trouble with a recently rebuiult carb and discovered this.

lars

That's correct. It's called the "20 horsepower floormat tuning trick," and I demonstrate it in all my Tuning for Beer seminars. That trick, along with several others, are outlined in detail in my paper for anyone who wants to see all the reasons for inoperable secondaries.

Lars