secondaries wont open

-
T

TimDart

Well-Known Member
Joined
Dec 17, 2005
Messages
359
Reaction score
31
Location
UK
hi Guys,
Bolted a holley 750 vac/sec onto my 360 this week.
Motor has 268 cam and air gap inlet, 3.23 rear.
for some reason the secodaries wont open.
Ive checked everything e.g linkage, diaphram, fitted weakest (white) spring and removed the ball check thingy.
Still no evidence of secondaries opening and ive driven the car all over today including full throttle kick down, cruising, lugging up hils.
Nothing seems to open 'em
ideas welcome
 
Holley says you really shouldn't feel the secondaries (vacuum) open, it should be a smooth transition.

This is from the Holley site:

"The secondaries will not open by free revving the engine. The engine needs to be under a load before they will open. If you are still uncertain if they are opening or not you can take a normal paperclip and clip it onto the secondary diaphragm rod. You will then push it up against the bottom of the secondary diaphragm housing, now you will need to go out and drive the vehicle. When you return you will be able to look at the position of the paper clip on the rod. If it is lower on the rod then you can tell the secondaries opened and how far they opened. This is useful in determining if you need a heavier or lighter secondary spring."

I'd also check to make sure the diaphragm isn't ripped or has a hole in it somewhere. Also make sure the o ring is in place to seal the cover. Another thing to check is that your throttle linkage isn't binding and that the cable is adjusted correctly to allow full throttle to be reached.
 
Can you open them by hand?

How do you know they are not opening? You won't see it by snapping the throttle.

That check ball is in there for a reason.

If all fails, could be contamination in a port. Remove and rebuild. Get a can of carb cleaner and blast out every port.
 
Years ago my buddy had the same problem with his 383. Turned out his intake was a square bore but his carb was a spread bore, so the throttle blades would hit the intake and not let them open...it is possible that is your issue ?
 
Ok,
I know that the diaphram is good. Removing the check ball is sometimes recommended for use with small vehicles
I know that they are not opening as i fitted a cable wrap around the lever against the diaphram housing. The cable never shifted.
Never thought about the throttle blades hitting the inlet. Its a eddy Air gap. would have though that it would be fine for the Holley but i wil check.
 
It's also common to see the secondary diaphram "folded over" under the cap. That acts like a giant vacuum leak and the secondaries will not open.
 
Just checked. The secondaries open if i turn them manually, so fitment to inlet is correct.
I checked the diaphram by taking it off the carb and sucking. That proved that the diaphram is good. so i guess folding isnt the case.
Other ideas welcome as i've been on this one all day without a result.
 
tim, i didn't catch weather you had removed the check ball? according to my holly book, you need that check ball in place.
 
After you have checked everything over and feel confident that they are or should be opening..... I would use a paper clip on the diaphragm arm so when you test drive it the paper clip will be pushed down the diaphragm arm. So when you pop the hood you can tell if they are opening and how much. I did this years ago on a Holley I had and it helped to diagnose a problem I was having.

You have to bend the paper clip a little and work with it but I think you get the idea.
 
edbux said:
Holley says you really shouldn't feel the secondaries (vacuum) open, it should be a smooth transition.

This is from the Holley site:

"The secondaries will not open by free revving the engine. The engine needs to be under a load before they will open. If you are still uncertain if they are opening or not you can take a normal paperclip and clip it onto the secondary diaphragm rod. You will then push it up against the bottom of the secondary diaphragm housing, now you will need to go out and drive the vehicle. When you return you will be able to look at the position of the paper clip on the rod. If it is lower on the rod then you can tell the secondaries opened and how far they opened. This is useful in determining if you need a heavier or lighter secondary spring."

I'd also check to make sure the diaphragm isn't ripped or has a hole in it somewhere. Also make sure the o ring is in place to seal the cover. Another thing to check is that your throttle linkage isn't binding and that the cable is adjusted correctly to allow full throttle to be reached.
Click to expand...

Thanks for that info...you guys know your stuff on these holleys....
 
Paer clip test was a bit wobbly. Ive used a tie wrap that is just firm enough not to slip and loose enoughto show if the secondaries are opening.
Replaced the ball check and fitted an o ring where the fibre gasket to the vacuum port goes , behind the diaphram block
Off to try again...
 
You must log in or register to reply here.
-

Back
Top