Frustrated!

[Paul A]

I am still chasing a vacuum leak! I installed an Offy manifold and a newly rebuilt Carter 400 cfm carb. Somewhere a small amount of air is entering! All vacuum ports are plugged on the manifold and carb. All new gaskets. All bolts torqued in sequence to proper values. I have had the upper manifold piece off a couple of times and it seems like the FelPro gasket is not compressed. I tried using shorter bolts to ensure they were not bottoming out. Following the advice posted by Dan R on the lower manifold piece I used the proper length bolts in the correct places and torqued them according to sequence and value. Frustrating!

I have made some progress and the engine will run about 1200-1250 rpms with a slight choke on the carb. The timing is close enough to run the engine but untill I can get it to keep running at 850-900 rpms it will not be spot on.

I may remove the upper manifold piece again, remove the Fel Pro gasket and use Permatex instead.

Just venting I guess! Any thoughts appreciated. I think I will have a home brew or two!!!

 

[DanR]

Paul A, What am are you running?

 

[Paul A]

Paul A, What am are you running?

what cam I think you mean stock cam for 1977 2.8 from a Mustang II

 

[DanR]

What grind? Jose or some other street type?

 

[DanR]

Paul A, Do you have an actual leak? Or is it just the engine does'nt want to idle below 1200?

 

[Paul A]

Paul A, Do you have an actual leak? Or is it just the engine does'nt want to idle below 1200?

I wish I knew what was causing the issue! Engine has run fine since I pulled it from the Mustang II and installed it
in Ol Blue. Stock cam, no special grind. Car ran just fine when I turned it off and began the manifold switch. With stock manifold and Ford carb the car will idle smoothly at 800 rpms.

 

[260Alpine]

You may have a leak down at the intake gasket at the heads?

 

[DanR]

Paul A, I just remembered that the OFY intake base has to be "fitted" to the heads. The angle sometimes changes when grinding or resurfacing which can cause different angles. Sven Pruitt has a not in his book about corrections you can take to remedy this. It may be your problem....

Give me a call.

 

[Paul A]

I just ordered the Pruett book. Found a used one for a decent price. The heads are factory, never been modified. The offy intake lower piece appears to be original as well. I will keep working and trying to find any leak while I wait for the book.

 

[Bill Blue]

Paul, are you saying that the engine runs at 1200-1250 with the throttle closed? If so, check to make sure the throttle plates are centered and indeed are closing completely.
Bill

 

[todd reid]

spraying with carb cleaner or brake cleaner will often help locate a vacuum leak - if that is in fact your problem. Several Utube videos available on the subject.

 

[husky drvr]

Paul,

I know nothing about Carter carbs or you installation, so this is a wild guess.

If your carb has the built in auto choke housing and you're not using it, there is a possibility a vacuum port is routed to that housing and would need to be sealed. This port would have been used to pull hot air to warm the bi-metallic element for the choke's operation.

Hope this helps,

 

[Mike O'D]

If you want to check for vacuum leaks, I would suggest putting a rubber tube on a propane torch and directing it at areas of interest - much less chance of having a fire!

 

[JMSiragusa]

I am following this as I had the same problem and ended up staying with the original manifold and carb set up. I would very much like to use the offy manifold setup so please let us know if and how you overcome this problem.

 

[Paul A]

I am following this as I had the same problem and ended up staying with the original manifold and carb set up. I would very much like to use the offy manifold setup so please let us know if and how you overcome this problem.

I have things torn down again - waiting for new gaskets

 

[gatkeper1]

What carb number are you using and which of the two Offy intakes?

 

[Paul A]

What carb number are you using and which of the two Offy intakes?

Carter AFB 4331s 400 cfm Rebuilt by my favorite carb shop near Minneapolis The Offy manifold is a dual port four barrel - 6096 lower with upper as pictured.