Rochester carb assistance

itbrokeagain · 04-11-2010, 06:43 PM

My cousin just bought a 79 Vette with a 4BBL Rochester. The secondaries are not opening. If I put a screw driver in there I cant open them. All the linkage seems to be connected and moving. Any tricks or do I need to pull it and try to get them working? This car sat for about 3 years.

cheech · 04-11-2010, 11:53 PM

There is a vacuum pull off and I think the choke linkage may restrict them. If you look at the secondary throttle shaft you will see a bell crank that, if I remember right is on the passenger side that prevents them from opening until the choke is fully open. So if it isn't running and no vacuum on the choke pull off they won't open. Mkae sure the pull off is working while running.

comanchedude · 04-12-2010, 12:12 AM

Quote:

Originally Posted by itbrokeagain

My cousin just bought a 79 Vette with a 4BBL Rochester. The secondaries are not opening. If I put a screw driver in there I cant open them. All the linkage seems to be connected and moving. Any tricks or do I need to pull it and try to get them working? This car sat for about 3 years.

The Q-jet has vacuum secondaries and they are designed to open when the engine really can take advantage of them,(wot mostly) so they wont open just by flipping the carb linkage.they open by vacuum only. hope this helps

cheech · 04-12-2010, 09:04 PM

They do not have vacuum secondaries! They have mechanical secondaries with secondary air valves that open according to engine air flow requirements, hence the extra set of butterflys at the top of the carb.

carwash · 04-12-2010, 10:00 PM

No vacuum secondaries... they are mechanical. At least every q-jet ive had has been. if you twist that throttle linkage about halfway they start to open... mechanically.

Even if they were vacuum actuated, he would be able to open them with a screwdriver for sure. Something is seized tony, or broken inside that linkage... take it off. Worst case, trade it in for a new one for $300 or so... Or i have a guy that can rebuild it for about $50 plus parts.

Bear Chow · 04-13-2010, 11:18 AM

There are several Corvette clubs locally. And meet bi-weekly at parking lots around town. I'm sure if you bring it to one of them they could bench rebuild it right there for you.

itbrokeagain · 04-14-2010, 01:25 AM

Yea I figured it was seized up. Even if it has vaccum secondaries I should still be able to manually push them open right?

Waffle · 04-14-2010, 01:25 AM

Doubt your going to find someone getting their hands greasy and gassy at the cruise-in.

http://www.carburetor.ca/carbs/tech/...jet-index.html

Secondaries are air......The basic 750 cfm carb is used from the 231 to the 400 because of this.

04-11-2010, 06:43 PM	#1
itbrokeagain Just Empty Every Pocket - CORE Member - Join Date: Feb 2007 Location: Amelia Posts: 1,435	Rochester carb assistance My cousin just bought a 79 Vette with a 4BBL Rochester. The secondaries are not opening. If I put a screw driver in there I cant open them. All the linkage seems to be connected and moving. Any tricks or do I need to pull it and try to get them working? This car sat for about 3 years. __________________ 91 fj 80 on 37 Nitto Muds with a 10k winch. Cage and sliders coming soon.

04-12-2010, 10:00 PM	#5
carwash pimpin' IS easy Join Date: Jan 2007 Location: Union, KY Posts: 3,344 Images: 605	No vacuum secondaries... they are mechanical. At least every q-jet ive had has been. if you twist that throttle linkage about halfway they start to open... mechanically. Even if they were vacuum actuated, he would be able to open them with a screwdriver for sure. Something is seized tony, or broken inside that linkage... take it off. Worst case, trade it in for a new one for $300 or so... Or i have a guy that can rebuild it for about $50 plus parts. __________________

04-14-2010, 01:25 AM	#7
itbrokeagain Just Empty Every Pocket - CORE Member - Join Date: Feb 2007 Location: Amelia Posts: 1,435	Yea I figured it was seized up. Even if it has vaccum secondaries I should still be able to manually push them open right? __________________ 91 fj 80 on 37 Nitto Muds with a 10k winch. Cage and sliders coming soon.

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04-11-2010, 11:53 PM	#2
cheech Join Date: May 2007 Location: cincinnati Posts: 18	There is a vacuum pull off and I think the choke linkage may restrict them. If you look at the secondary throttle shaft you will see a bell crank that, if I remember right is on the passenger side that prevents them from opening until the choke is fully open. So if it isn't running and no vacuum on the choke pull off they won't open. Mkae sure the pull off is working while running.

04-12-2010, 09:04 PM	#4
cheech Join Date: May 2007 Location: cincinnati Posts: 18	They do not have vacuum secondaries! They have mechanical secondaries with secondary air valves that open according to engine air flow requirements, hence the extra set of butterflys at the top of the carb.

04-13-2010, 11:18 AM	#6
Bear Chow Jeepless Join Date: Feb 2007 Location: Oxford, Oh Posts: 302	There are several Corvette clubs locally. And meet bi-weekly at parking lots around town. I'm sure if you bring it to one of them they could bench rebuild it right there for you.

04-14-2010, 01:25 AM	#8
Waffle Join Date: Aug 2009 Location: . Posts: 75 Images: 10	Doubt your going to find someone getting their hands greasy and gassy at the cruise-in. http://www.carburetor.ca/carbs/tech/...jet-index.html Secondaries are air......The basic 750 cfm carb is used from the 231 to the 400 because of this.