Vacuum secondary issues

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partsman1965

partsman1965

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Do I need a double pumper? I have an 770cfm street avenger with vacuum secondaries and they will not open. I have in the lightest spring and everything is free and fresh. The car is 340 flat tops with 2.02 J heads with mild porting and MP .484-262 hydraulic cam.
 
Are you sure they are not opening? typically the vacuum secondaries will not open with it in neutral and revving the engine.
 
You can test the secondaries with a zip tie. Tie a zip tie around the vacuum secondary pull rod (up at the top). If the secondaries open when you're driving, the zip tie will be pushed down the rod.
 
spl440 said:
Are you sure they are not opening? typically the vacuum secondaries will not open with it in neutral and revving the engine.
Click to expand...
Put a tie wrap on the small diaphragm rod up against the bottom of the housing. Put it on just snug enough to hold without falling. Take the car for a ride and get into it. if the secondary's are opening the tie wrap will have moved down the shaft away from the diaphragm housing.
 
Aaron65 said:
You can test the secondaries with a zip tie. Tie a zip tie around the vacuum secondary pull rod (up at the top). If the secondaries open when you're driving, the zip tie will be pushed down the rod.
Click to expand...
Dang! beat me to it Aaron! Lol
 
Funny but that is how I tested it already. I then I put a small screw in the slot on link at about 3/8 throttle and they open once the link pushes on the screw.
 
Ok. Your secondary's might be seated to tight in the base plate. Check the small adjustment screw to make sure the secondary's are cracked open a bit.
 
I think you need a 670 holley at the most.If your carb is to big your secondaries will not open even with the lightest spring.
 
Check to be sure the small round cork gasket is in place between the main body and the vacuum diaphragm housing, I put some sticky on it so it doesn't fall off while assembling after changing the spring...

Also check that the rubber diaphragm is properly sealed and hasn't pulled back off the housing when putting back together.... Or any places that it may have come back and not seal on the housing...
 
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