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

Not that I know of but you need to do a search for it.

That is not a common item at all.

quote:

That is not a common item at all.

Yeah, I know. It would be nice to have a non-metallic spacer to help reduce the heat transfer to the carb.

John

Spoke with Jegs a few minutes ago, and this is what they suggested. Apparently aluminum bodies are cheaper !!

http://www.jegs.com/i/Holley/510/0-80508SA/10002/-1

Thoughts?

Too shinny. Vintage Holleys should be gold, not purple or polished!

Put a Holley spread bore on it if you don't want to screw with the intake manifold and the air cleaner.

What's the difference what size you use? The original carb is a 600 cfm. The 1850 is the least expensive of all the carbs. You can even buy them "Factory rebuilt" on ebay.

This guy is just going to cruise around in it.

The Offe manifold is lower than the Edelbrock.

All of these manifolds are within 10hp of each other on a street car so if you do a manifold go with fit.

There is an original aluminum Ford manifold with either a spread bore pattern or a square bore. Buy one on ebay.

It is really the same manifold as the iron, just in aluminum. The iron is better if you drive it in cold weather. The aluminum will allow the carb to ice up. Not the best for a everyday driven car.

I find Summit is cheaper on everything over Jegs. You should compare before you buy.

I have pretty much just gone through this and as mentioned you will need to use an adaptor plate to fit that carb to the stock manifold. With a 600 vac sec and stock air cleaner it no longer fit under the stock engine screen. So I have changed to the edelbrock performer intake and 670 ultra avenger and due to the adjustable float bolts the stock air cleaner no longer fit. I bought a 14" drop base air cleaner and it does not fit as the dizzy cap gets in the way. I ended up with a chrome ford racing 13" drop base and that fits well. And it all sits neatly under the screen.

As for the carb I would see if they have any ultra in that make. The ultra is almost half the weight and has float side glasses as standard. Looks damn sexy in blue as well.

However I probably not get the Avenger as I have had a few issues which I don't think should have happened. The first is that the Avenger ultra has an idle circuit on the secondaries. I was told to leave it well alone but with the curb idle screw adjusted out fully it would not idle below 1200 rpm. This in turn caused the accelerator pump control arm to ride on the throttle plate spring and the accelerator pump would not actuate for about an eighth of a turn of throttle. Which then caused a flat spot off idle. So I had to remove the carb to adjust off the secondary curb idle screw. I backed it off so that the secondaries are fully closed and it now uses just the primary idle circuit. Now I can back off the the idle properly and the accel pump arm rides much less on that spring and with a slight bend of the arm it works correctly. Far too much mucking about for something that pretty much should bolt straight on! Now I just need to play with jetting.

Owner of the car wants to stay original. Dispensing with the commentary on that (and I agree that a substitute is the correct path), I still need help. I pulled the carb today, found everything in order (as far as I can tell), re-installed it, and it hung up under full throttle. And that was after about a 3-4 minute warm up. Throttle cable is NOT the issue (checked it). I can not imagine that incorrect vacuum line routing could cause this, although I am equally confident that the hose routing is correct. I have a Contour digital camera so I may point it at the right side of the carb as see what the linkage on that side is doing. I'm stumped. Everything is fine until I hammer the gas pedal.

Bob

is this a 4300A (square bore) or a 4300D (spread bore)?

I forget which year model car you're working on.

-G

Hi snaponbob,

to be sure i understand the problem, when you say "it hung up under full throttle" you mean it continued to run at high speed after the gas pedal was released as if the carb did not close. Is that correct ?? How fast does the engine run ?? Flat out ? 2000rpm ? 3000rpm ?

I understand you have checked the throttle blades are fully closing, that's good, that eliminates linkage problems, and tells you the carbs main systems have shut down. Main systems run on air flow, they just can not run with the blades closed.

I spoke previously about a vacuum leak, i was not referring to a external leak in vac hoses for accessories but rather a internal vac leak though one of the systems of the carburetor.

You were saying you pulled the carb today and all looked in order, it will.

There will be no obvious fault a visual inspection will reveal. Carbs are like that, i've worked on many that look perfectly fine when stripped down but wouldn't work for love nor money when put back on the engine.

I've had carbs that worked fine for years on the same engine and then played up in every way and it wasn't dirt, crud, broken gaskets, leaky needles/seats, damaged o-rings or any of the other obvious stuff that comes to mind, in the end it took complete recalibration of the carb (which goes against all reasonable logic) to bring them back to working order.

Carbys are actually a analogue mechanical computer and when you come across a difficult one like the 4300 you have you have to really get your mind around how all the circuits in the carburetor work and how they work in conjunction with each other to either find the source of the problem or do something to compensate for the way the carb is behaving.

Strip the carby down and while it is apart make a drawing in as much detail as possible of the various circuits in the carburetor including all the components and their methods of actuation and their relationship to each other.

You will need to look at:
idle jets, idle air bleeds, idle emulsion tubes and compensation system, idle screws, idle ports, transfer ports, throttle blade relationship to transfer ports, main jets, high speed air bleeds, main emulsion tubes and compensation system, fuel enrichment system (power valve), accelerator pump and check valves, hot idle compensator, secondary air valve system including damper.

As a last thought you may want to try reducing the size of the idle air bleed restriction, this will reduce the air going into the idle compensating circuit richening the idle mixture, you will then have to close the idle mixture screws slightly (maybe 1 or 2 turns depending on how much smaller you make the bleeds) and open the throttle blades slightly. This will reduce the air bleeding into the engine through that system when the throttle blades slam shut.

It sounds to me like there is air bleeding through one (or more)of the carbs circuits taking fuel with it in sufficient quantity to make the engine race on closing of the throttle. You have to find which circuit is allowing this.

quote:

Originally posted by George P:
Bob

is this a 4300A (square bore) or a 4300D (spread bore)?

I forget which year model car you're working on.

-G

Spread bore.

@ Aus Ford - from the list of items it makes me remember jetting and sorting a 45 DCOE Weber !!!!

Trade it in on a rebuilt one or take it to a Motorcraft re-builder if the owner needs to have the original carb.

If it were me in your position now I would have to throw in the towel and say that it is beyond my capabilities.

Getting close !!!

quote:

Originally posted by snaponbob:
@ Aus Ford - from the list of items it makes me remember jetting and sorting a 45 DCOE Weber !!!!

That's it you've got it now, treat the 4300 like it is a DOCE.

I think if you can get hold of another 4300 you can try that may be a help but i think getting the one you have "professionally rebuilt" will be a waste of time and money, all they will do is put a gasket kit though it, it won't be any better than what you have done yourself.

These "professional rebuilders" almost never go into the detailed inner workings of a carb, you could wind up with the carb rebuilt but just like it is now.

IT'S SORTED !!!!!!!!!!!
Two apparent issues -
First, the manual says the idle solenoid is not strong enough to effect the idle. My comment on that - my ass it won't !!!!!!
Second, The spring in the choke may not have been in the slot of the linkage in there. It may have been NEXT to the arm in such a way that it would close the choke when cold and then float around when warm.

In any event I have been sort of hammering around in the Pantera for about 30 minutes of "spirited" throttle use with no surprise. Thanks for the input, everyone.

Great news!
Im still driving with 4300 and its "fun".
Problems are usually mechanical and simple, you just have to spot them.

quote:

the manual says the idle solenoid is not strong enough to effect the idle.

The idle solenoid isn't strong enough to rotate the throttle shaft when the key is turned on, energizing the solenoid. Once the throttle shaft is rotated (with the solenoid energized), the solenoid will keep the throttle shaft rotated slightly until the key is turned off. This is to help control dieseling.

John

quote:

Originally posted by jb1490:

quote:

the manual says the idle solenoid is not strong enough to effect the idle.

The idle solenoid isn't strong enough to rotate the throttle shaft when the key is turned on, energizing the solenoid. Once the throttle shaft is rotated (with the solenoid energized), the solenoid will keep the throttle shaft rotated slightly until the key is turned off. This is to help control dieseling.

John

I understand all that, but the one on THIS car is STRONG !!!! It WILL push open the throttle at idle, so I have adjusted accordingly. What is interesting is that the car idles at different RPMs dependent on engine temp. Weird.

quote:

I understand all that, but the one on THIS car is STRONG !!!! It WILL push open the throttle at idle, so I have adjusted accordingly.

I forgot to mention that you are supposed to set the hot idle speed at the solenoid, not the carb.

John

[/QUOTE]What is interesting is that the car idles at different RPMs dependent on engine temp. Weird.[/QUOTE]

There is a thermostatically operated valve that provides a vacuum source to the distributor from either the carburettor venturi or the inlet manifold depending on the engine temperature.

It is usually set up so that when the engine gets hot the distributor receives manifold vacuum, the theory is this speeds up the idle speed to run the fan (on normal sedans) and water pump faster thus helping to bring the temp down.

I have heard on Panteras it is some times set up the opposite way (i'm not sure why) but this feature will cause the different idle speeds at different temps either way it is set up.

I don't know what the shop manual says about it but at one time I used the Boss 302 idle solinoid on the Holley set up and it absolutely pushes the throttle open to the extent you have it adjusted to.

It is there, in my case, to close the throttle more then the standard idle adjustment screw setting.

The reason is that in order to get the idle lean enough for emissions, the factory set up tended to have the car run on after the ignition was turned off. In many cases this would mean the carb would dump a noticeable amount of unburned fuel into the intake manifold.

That was negative for a few reasons. 1) it tended to flood the engine on hot restart 2) as a result it tended to foul the spark plugs 3) would show negatively on the idle tail pipe emissions test which eventually came in California first in '75, then the US in '76.

The solenoid is definitely strong enough to set the idle position by just turning on the ignition switch. Absolutely.

You set it cold because it works in conjunction with the choke cold fast idle positioning.

Most people don't get that right to begin with. That cold fast idle is supposed to be 2,200 rpm and most try to set it down thinking it is too high.

That's where the problems start, particularly on the BB cars with automatic transmissions. Customer complaints were that you couldn't stop the car when it did that.

Manual transmission cars theoretically don't have that problem BUT I know of one Pantera that was totaled out at the dealer, by the dealer because of this in White Plains back when the car was new.

The location of the engine in this case makes the Pantera very difficult to work on to get it right right off of the bat.

These set ups were already installed on the engines as delivered to DeTomaso and Ford told them to leave them alone and install the engine the way they got them, so no work on the idle was supposed to be done on them.

IF they got modified it would have been due to what the dealer's service department did in relation to a customer complaint.

When the engine gets "rebuilt" after the fact and everything was disassembled, that's where these issues come in. There are a lot of connections that need to be done as designed otherwise you are in for a living Hell.

There are very, very few "original stock" Panteras left for a reason. Sane people got rid of these set ups YEARS ago.

Only an anal S&M master would demand it to be put back to stock. S&M costs the customer way over the standard rates in this shop!