Exciting -------------- when the throttle hangs up !!

Is the carb a 4300 ?

Maybe try a heavier external return spring ??

Oh, heck no. That is a Holley double pumper.

The carb in the pic is actually a Holley 600 vac secondary.

I just used this photo as it showed the external spring fairly well. (which is a stock Ford item)

Is the carb you are having problems with a 4300 ?

Yup.

Externally, the primary linkage shows that the arm has returned to the throttle stop. I am wondering if the vacuum system for the secondaries is hanging up. Only happens when the throttle is pushed well past half throttle.

Once shut off and re-started, it's a 50/50 that it will idle properly.

4300's can have a percolation problem in the float bowl after being shut down which can lead to excess fuel in the manifold on start up and thus hard starting and poor idle for a while after start up.

It can be remedied somewhat by float level ajustment but if lowered too much that in turn can lead to a excessively lean condition.


If shut off again, and waiting 30-60 seconds, it's more likely to idle okay until hard pedal application.

I am wondering if the vacuum system for the secondaries is hanging up. Only happens when the throttle is pushed well past half throttle.

It's worth a look at the piston and spring for the secondary vac plates (Air valve damper piston) to be sure they are free and working correctly but in themselves the secondary vac plates wont make the engine run uncontrolled if they are stuck open (they will only make throttle response terrible)

The throttle blades themselves must be open for uncontrolled engine speed, if the blades fully close all the wizardry in the carburettor that is above them ceases to function and the engine will slow down, so if the engine speed is uncontrolled (seems like the carb is hanging up) primary or secondary blades must not be returning to fully closed.

That doesn't need to be very much when the car is in neutral, just a fraction open (1/16" inch or even less) will make the engine race.

There could be a internal vacuum leak somewhere that is only taking place after the carb has been opened up and the engine revved up.

If that leak continues and there is enough fuel available it will act like the carb as not fully closed back to the stops.

You may want to check the 4300s power valve (auxiliary valve)for proper functioning and possible vacuum leaks into that part of the system.

Also check out the "hot idle compensator" if it has one. It's the bimetal spring gadget at the back of the carb in between the secondary barrels.

check for foreign debris in the primaries. Might have a screw fallen in there unnoticed and holding the throttle plates open, then rattles around enough to get out of the way.

hey this is exactly the same problem as I had in 7207. problem was actually a bad spring on secondaries. when you cut the ignition the vacuum of the engine close the seconderies. a simple test for this is. get the problem to occur in our garage. use your finger to press down the secondaries butterflyes and see if the idle goes down to normal.

quote:

Originally posted by PanteraDoug:
check for foreign debris in the primaries. Might have a screw fallen in there unnoticed and holding the throttle plates open, then rattles around enough to get out of the way.

The thought of a piece of something in the intake is frightening !!!!! Since this is a repeating problem I sort of have to assume it is a carb issue, not a foreign object. Carb will be coming off tomorrow, so lots will be checked. There is a piece of linkage on the right side held on by a wide headed flathead screw that I think I have wrong.

quote:

Originally posted by Lofoten:
hey this is exactly the same problem as I had in 7207. problem was actually a bad spring on secondaries. when you cut the ignition the vacuum of the engine close the seconderies. a simple test for this is. get the problem to occur in our garage. use your finger to press down the secondaries butterflyes and see if the idle goes down to normal.

Ding ding --- maybe a winner. When this happens out on the road the engine pulls as hard as the brakes will retard the car, and the booster runs out of vacuum. Exciting.

It is your call but you will find the vast majority of Panteras had the original carb replaced decades ago.

There is a reason for this and that reason is the original carb is a piece of junk.

A simple 1850, 600 cfm Holley carb will make the problem go away.

The owner can demand whatever he wants but if you are dead and the car is wrecked, somehow I think that he might have second thoughts as to what to demand?

No one in their right mind wants a completely orignial Pantera except maybe Lee Iaccoca?

quote:

No one in their right mind wants a completely orignial Pantera except maybe Lee Iaccoca?

Or someone that doesn't intent to drive it much...

Thank god most of us like to be different and march to our own tune!!!

Marching is acceptable but no skipping ok?

Actually I would have loved to keep the original carb except mine only worked when it idled or when it was flat out. Well the first few drives were a lot of fun however one of my neighbors gave me a dirty look as I went sideways past his house.

quote:

Originally posted by PanteraWanabe:
Actually I would have loved to keep the original carb except mine only worked when it idled or when it was flat out. Well the first few drives were a lot of fun however one of my neighbors gave me a dirty look as I went sideways past his house.

In a perfect world everything and everyone is perfect.

"Those who refuse to learn from history are doomed to repeat it." -
Winston Churchill

I post here to share my experiences. Your's may vary, but remember I warned you?

quote:

Originally posted by PanteraDoug:
It is your call but you will find the vast majority of Panteras had the original carb replaced decades ago.

There is a reason for this and that reason is the original carb is a piece of junk.

A simple 1850, 600 cfm Holley carb will make the problem go away.

The owner can demand whatever he wants but if you are dead and the car is wrecked, somehow I think that he might have second thoughts as to what to demand?

No one in their right mind wants a completely orignial Pantera except maybe Lee Iaccoca?

I am going to take another swing at getting it working. Your assessment of "junk" IS correct. I will look at the Holly. Is that a straight bolt up? Assuming so, does one just cap off the metal line to the choke?

It is a square bore mounting and your's is a spread bore pattern. Most people swap the manifold out also.

Simplest is to put the Edelbrock intake on OR go to a Holley GM style spread bore carb.

http://www.summitracing.com/parts/hly-0-80555c

You could get an adapter plate from Summit Racing as a simple solution.

You can connect the choke tube to the Holley. Theoretically it warms up faster with it but I think it is redundant.

That pic i put up earlier of the Cleveland with the red rocker covers has a spread bore manifold with a 600cfm squarebore Holley.
The adaptor plate is about 7/8" thick. It worked pretty well. It would have the advantage that if the owner does want to swap the carb back the original manifold is still there.

http://www.summitracing.com/parts/edl-2697

There are cheaper ones but you get what you pay for.

Does anyone sell a phenolic (non metal) spread/square adapter ??

John