4mv secondaries not opening all the time
Thread Starter
2nd Gear
Joined: Sep 2012
Posts: 2
Likes: 0
4mv secondaries not opening all the time
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?
Any thoughts or ideas as to what could be causing this?
Thread Starter
2nd Gear
Joined: Sep 2012
Posts: 2
Likes: 0
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?
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?
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
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
Lars
V8FastCars@msn.com
Le Mans Master
Joined: Aug 2010
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Race Director
Joined: Apr 2011
Posts: 11,183
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From: North of Toronto - Ontario
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
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
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
http://www.arkansaspontiacs.org/tech...ockyQ-jets.htm
interesting reading
interesting reading
Q-Jet secondaries are not vacuum operated. Complete, correct, description outlined in my paper.
Lars
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Burning Brakes
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From: Morgantown,WV USA
4mv secondaries not opening all the time Reply to Thread
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?
Any thoughts or ideas as to what could be causing this?
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
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
Lars