[BlackStick]

I think (actually pretty sure) I have a leak but am not getting far in locating it.

The motor idles at about 1000 rpm but after warming idles at 13-1400. Mileage is unbelievable bad. Terrible stumble between 2-300RPM unless I am on it...

The only vacuum line I have is for the power brakes and comes off the intake at the individual runners for number 4 and number 8 cylinders. Out of curiosity I put a vacuum gauge on the connect and found I had 20 with a slight pulse. I think the pulse is from this being two individual intake ports.

I checked and discovered that all 16 carb hold down bolts were relatively loose. I had to turn everyone atleast 1/4 turn to make them just good-snug. I only checked one intake (front, near number 5) and it was tight. I have no reason to believe the others may be loose but perhaps. When I installed the intaks I torqued all of the bolts three times. On a Weber set-up this is really a PIA because of clearances to get to the bolts.

I bought some German vacuum leak finder but have not tried it yet. It is supposed to bubble "more" when there is a leak. Depending on time I will try this on Sunday or Monday. I amd trying to finds some spray carb cleaner or starting spray since I am much more familar with using this for vacuum leaks.

Can it be that the carb/manifold gaskets need to be replaced due to the possible leak? Should I seal them?

Anyone have other suggestions on next steps?

 

[j persons]

When you installed the intake manifold did you wait a day between torquing it down. The intake gaskets will "relax" but it takes about 24 hours before re-torque to insure they will stay at the desired torque.
What carb gaskets did you use? There are some available that are rubber coated that seal better than the paper ones. I used spring loaded carb nuts to secure the carbs to the manifold on a DCOE application. I'm unsure if they can be used for IDA carbs.

Some IDA Ford manifolds have a steel spacer plate glued to the manifold where it mates with the cylinder head. This plate should be removed, cleaned and resealed with a good quality RTV sealant.

 

[BlackStick]

I used a Fel-Pro gasket that had raised sections on the manifold side and did not wait to torque it. I did torque it twice however. I am thinking to remove the manifold and then put sealer on both side of the gaskets. Couldn't find any starter fluid here so I ordered some to see if I can localize the problem before tearing this down. Also want to pull the plugs and see if I have some cylinders that are running lean. The nice thing about the Webers is that if a cylinder is running leans I have a good idea where on the manifold it is leaking....

 

[rpm]

Here is a fail proof intake install how to.

How to Install an Intake Manifold on FORD 289, 302 and 351W Engines - MustangSteve

This page will walk you through the necessary steps to install an aluminum intake manifold on a 289, 302, or 351W engine. Get everything spotlessly clean and be sure to clean up all gasket debris from the lifter valley. A shop vac works well to suck any gasket pieces from the lifter valley and...

mustangsteve.com

 

[BlackStick]

This was my plan exactly. Last time I used sealant only on the ends around the water ports and did throw away the cork pieces..