I would check valve clearance.  This sounds like the same ptoblem I had and when I checked the clearance most of the valves had "closed" up.

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

I know the problem is related to the low vacuum. I have disconnected and plugged all the vacuum lines and tried the propane torch trick all around the intake manifold and carb.



When I turn the idle mixture screws all the way in the engine dies. If I had a vacuum leak I would think that opening the screws would smooth it out, but it does not.



I will check the valves this weekend and see if that does anything.



thanks

Dave Christensen

Dave Christensen

Falllbrook CA

57 Tbird

You can check power valve by turning mixture screws all the way in.Motor should quit.If not fuel is still comming in from somewhere besides the idle circuit.Power valve maybe.

  

Charlie:

The timing marks on a T-Bird are not on the damper ring, rather they are on the pulley itself.  Cannot slip.

Dave:

Perhaps the power valve diaphragm or the gasket is leaking.  A little richer mixture can be tolerated when cold, but warm it becomes a problem.

John - "The Hoosier Hurricane"

Hello Pete! If the valves are too tight to start with.As it warms up the clearance closes even more.Would that not cause the vacuum reading to drop?What was the problem with "getting the intake to seal" when you had it apart?Timing can also be set with a vacuum gauge.Slowly advance the timing until the highest steady vacuum reading.Back it off until vacuum starts to drop.Set timing halfway between high and drop point.Old time mechanics sometimes still set timing this way.

  

Dave

   You write that you have a rough idle and "When I start the car the manifold vacuum is steady at about 17 inches Hg at idle. As it warms up it drops to a steady 14 inches Hg. The idle gets worse as it warms up."

   Start there. Try to fix the vacuum leak first. Until you do eveything else will only be a waste of time. You may or may not have other issues but until this is fixed you do not know. Pete

Do you know the condition of the crankshaft damper? The damper ring can slip and falsely indicate the timing. Does it run better if you set the timing by ear?

Is the firing order correct?


Lawrenceville, GA

It has never idled smoothly. It is getting worse. It is bad enough for me to try doing something about it now. I had problems getting the intake manifold sealed when I had it off awhile ago. I tried the propane torch (unlit) next to all the runners and could not find a leak.



I have not checked the valve clearance since it has gotten worse. A couple thousand miles ago it was OK.



thanks

Dave Christensen

Falllbrook CA

57 Tbird

Thats a good suggestion from Charlie.Pay special attention to that lower compression cylinder.I was thinking vacuum leak.Check the adjustment first and then check around manifold or carb for possible leak.A burnt valve would cause the vacuum gauge to change each time that cylinder fired.

  

Has it ever idled smoothly while in your ownership?

Have you checked your valve adjustment?


Lawrenceville, GA