So I have set out to get the flapper on my cowl hood to work. I made the fitting to the intake manifold ran it through the valve and into the cowl diaphram. All parts were purchased from OPG.

Problem:
Looks perfect until I start the engine. The diaphram pulls door shut and does not release it. It is as if there is too much vacuum. Even with bringing the RPMs up and down the flap stays shut.

So far i tried:
- running the line directly to diaphram (Bypass the check valve)
- turning the valve around (perhaps my directions were incorrect)
- Clamping the hose and releasing the clamp slowly

The only way i can get it to work is pull the hose out from the valve and slowly attaching and detaching it allowing the vacuum to leak.

Is there a way to adjust the diaphram? It seems very sensative.

Any help would be appreciated,
Willy

Willy,
It sounds to me as if you are not dropping the vacuum FAST ENOUGH.
There needs to be a sudden drop in manifold vacuum going to the vacuum pod.
When you're driving, and under HARD acceleration, or full throttle (heavy load on the engine), the manifold vacuum drops off to nearly nothing.
The check valve that goes in the hose BETWEEN the vac pod and MANIFOLD vacuum only goes one way.
Remove the check valve, suck on it. One side will flow easier than the other side. The side that has the MOST resistance to sucking goes TOWARD the engine.
The way the check valve works (supposed to work) is to allow vacuum to go to the pod sloooooooooowly.
So, either with the check valve installed or not installed, try YANKING the throttle ALL the way open and see if the pod opens. With the car sitting in neutral (no load on the engine), when you yank the throttle wide open, then release it, the manifold vacuum is going to return quickly, thus, the door won't open much. There needs to be a load on the engine when the throttle goes to wide open so that manifold vacuum drops WAY DOWN which will allow the door to fully open.
From what you've mentioned, the vacuum pod is working correctly. You say that with the vac hose disconnected, it opens, then when the vac hose is connected, it closes. That is the correct operation. So, as long as there is good vacuum to the pod, it SHOULD remain closed until you open the throttle suddenly or under a heavy load. :thumbsup:

What Tom said.

You're not going to see much door movement without the engine under load and throttle open.

Just out of curiosity I hooked my Mytivac to the vacuum pod. It took under 3" and probably closer to 2" of vacuum to hold the door closed.

My first thought is that you had a 'true' check valve but you eliminated that possibility. With the system hooked up if the door is opening when the engine is shut off I would say the system is working correctly.

You do have the spring on it right? The door will only open under a engine load. It will open a little on a hard rev but in 4th I can floor my car and the door pops open and stays open until 100+mph

make sure you have wide open throttle.Meaning,when the gas pedal is all the way to the fllor,the linkage at the carb is open all the way too. If not,loosen the throttle bracket at the carb and move towards the firewall until you do.

It works. I was expecting it to move a little bit more on around town trips.

Thanks for everyones help.
Willy

I got the opposite problem. Since the 288/296 Ultradyne cam swap mine has a mind of its own:)

I have a problem with mine also,changed the carb from a 750 to a 600 cfm and now the flapper dosn't move at all,seems maybe there isn't enough vacum now ,I didn't change anything else.
Any ideas ????????????????

The cowl induction vacuum hose gets hooked up to the back of the manifold at the vacuum tree. This gives it full vacuum and if you floor it or go under a load (go up a hill) then manifold vacuum drops and the door will raise. The door should pop up when you shut the car off and close when you start it.

I have a problem with mine also,changed the carb from a 750 to a 600 cfm and now the flapper dosn't move at all,seems maybe there isn't enough vacum now ,I didn't change anything else.
Any ideas ????????????????

do you have wide open throttle as I mentioned? If you don't,the outer door will NOT open!

I have a problem with mine also,changed the carb from a 750 to a 600 cfm and now the flapper dosn't move at all,seems maybe there isn't enough vacum now ,I didn't change anything else.
Any ideas ????????????????

Also make sure your vacuum line isn't crimped shut. Sometimes if you move the line from where it's intended to be the hood will crimp the line when you close it.

do you have wide open throttle as I mentioned? If you don't,the outer door will NOT open!


Does this mean that the flipper will not even close when you start the car ????????

Does this mean that the flipper will not even close when you start the car ????????

engine vacuum keeps it closed...without wide open throttle,you will never reach the near zero vacuum point at which the flap starts to open.

Does this mean that the flipper will not even close when you start the car ????????

If your actuator vacuum line goes to the carb, you might have it hooked to a ported vacuum source instead of full manifold vacuum. If you're hooked to the right vacuum source, the door should shut as soon as the engine fires. If it doesn't shut, the hose might be pinched between the hood and the firewall.

The factory used manifold vacuum to operate the flapper door.

http://www.elcaminostore.com/technical/70-72cowlhood/33.jpg

Check out this Tech Article (http://www.elcaminostore.com/technical/70-72cowlhood.asp) for assembly and function.

you might need to bend the top of the cowl flat where the hose rests on it when closed. it could be getting pinched. watch the flapper when you pop the hood open w/ the motor off, if it pops open, thats the problem.