Idle Problems

1. what size jets are in the cab. Sounds like you may need to swap them for smaller size jets.
2. you may have too small an idle air bleed screw
3. have you adjusted your secondaries to let more air in at idle.

Did you buy the car with the carb conversion on it or did you convert it after you bought it?

Start by capping off every vacuum fitting on the intake manifold except the one that the vacuum gauge connects to. That includes the power brake booster and PVC or whatever you are using to vent the crankcase.Then start the car an see what vacuum you get - 13 " of vacuum is very low.

Start by confirming all fuel screws are set near the same. (example 1 1/4 out from lightly seated)
With the car warmed up and vac. gauge connected,turn all fuel (2 or 4)screws very slightly richer,and note vacuum reading. If the vac gauge did not drop,continue richer in tiny increments. When the vac. drops slightly try that.

If i read that right.
You are releasing the clutch without giving it any gas,and wonder why the revs are dropping ?

With a mild/moderate cam it should be steady. I am 244/252 @.050 gauge is steady.

You mentioned not being able to raise the idle. Any chance you have the idle screw turned very far in,uncovering the transfer slot ?

It is a ''dance'' to get it all right.
A question. In your first post you say,14 initial,23 mechanical,37* total ? A lot imo
And all in at 2500 may be asking for trouble. Do you all so have vacuum advance ?
And if so,ported or manifold ?

I'm wondering if you don't have a slipped lower intake gasket.

I don't say it's the problem,but i would back it off some until it is more sorted.
With no vac advance you want a fair amount of initial,but i would limit total to 32-33*
All in 3k+ (i am 30*,427 tfs heads)

14* should be ok,have you looked at the plugs ?

There is no easy way to find vacuum leaks. It is a time consuming job that requires close inspection of each and every hose and connection.

Small vacuum leaks may not show much change using a vacuum gauge. The range of "good readings" varies so much from engine to engine that it may be difficult to detect small leaks. The engine in my first Mustang pulled about 16.5" of vacuum at 650-725 RPM, which I consider rather low. It was a mass market remanufactured rebuild, so no telling what kind of camshaft it had. Average readings seem to run 16"-18" inches at idle and 18"-21" at 1000 RPM. The only sure comparison is a reading taken when your car was performing at its best through all the RPM ranges and what it is doing now. Use one of the spare ports on the vacuum tree that is mounted on the firewall near the windshield wiper motor.

Use a squirt can of motor oil to squirt around the mating surfaces of the manifold & TB. The oil will be sucked into the leaking area and the engine will change speed. Avoid using flammable substitutes for the oil such as starting fluid, propane or throttle body cleaner. Fire is an excellent hair removal agent, and no eyebrows is not cool...


Vacuum leak due to slipped lower intake manifold gasket...

Ask Nicoleb3x3 about the intake gasket that slipped out of place and caused idle and vacuum leak problems that could not be seen or found by external examination. I don't care what you spray with, you won't find the leak when it is sucking air from the lifter valley. It simply isn't possible to spray anything in there with the lower manifold bolted in place.





Determining if you have a leak due to a slipped intake gasket as shown above. This test is only good if you can get the engine to run somewhere in the 1000-1700 RPM range
If your valve cover oil filler & PVC systems are still in the original configuration, try this:
Cap or plug the hose from the intake manifold to the PVC valve with a bolt.
Cap or plug the PVC valve with a piece of hose with a plug or bolt in it.
At that point the only vent for the crankcase is the tube from the oil filler neck to the throttle body.

Disconnect the tube that runs from the oil filler neck to the throttle body. Make sure the oil filler cap is on securely. Start the engine and put your thumb over the end of the tube that comes from the oil filler cap. If you feel suction, there is a leak. Another thing to do is to extend the tubing from the filler neck so that there is enough to stick the end in a jar or cup filled with motor oil. If it sucks up the oil, you definitely have a leak at the underside of intake manifold.

This isn't necessarily the definitive test, but it is the best thing I could come up with on short notice. If there is a lot of blow by, this obviously won't be of much help.