Barry Grant/Holley 750 Double Pumper Base Plate Question

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Psychoduster

Psychoduster

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Hi,

I need to do some tuneup to the 750 Barry Grant (Gold Claw) double pumper, because the throttle blade shaft is leaking.
All 4 blades are stamped 1.69, but unfortunately I can't find more Infos on the base plate (numbers, letters, etc.).
Can someone please help me to identify the item?
I want to buy a new one, I don't want to rebuild it.
All base plates I found have the 1.75 blades (for example: Holley-QFT-AED CCS Billet Base Plate Assembly 1 11/16" 650-800 CFM Carburetors | eBay)
I think it would't be helpfull to select bigger blades.
Because I live in Germany, it isn't that easy to get Infos from a local shop :)

The best match I found is the base plate for a 750 Mighty Demon: Demon MAD-750-B2 750 CFM Aluminum Mighty Demon Carburetor

Here are some pictures of the part - Carb is stamped A12401

Workes great on an 1973 Duster, with 1979 360, 0.030, Speed pro Pistons (10,0:1), Comp Cam 292....

Thanks in advance, Eckhard ;-)

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Holley ,bought Barry Grant.. .. Easy response, E mail Holley ... Calling is a pain ,in the ***.
 
So,the real question: What's wrong ,with the current base plate ?.
 
Abodybomber said:
So,the real question: What's wrong ,with the current base plate ?.
Click to expand...
The current base plate is leaking fuel , between the shaft and the lever.
Every time I move the blades, a few drips of fuel are leaking and wetting the Edelbrock air gap manifold..... and I don't like free fuel on hot surfaces :rolleyes:
After a few minutes of driving, it's getting ugly and after half an hour I have a litle sea of fuel under the carb on the manifold......

Regards, Eckhard

BTW, I know the BG story and a few month ago I had contact with him, but that wasn't realy helpfull....
 
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Ok.....

did some research and the base plate I'm looking for is from a Holley 5402010GC 750 Mighty Demon.
Thought here are some carb cracks arround :D, but if someone has the same problem.... that is the solution.

Regards, Eckhard
 
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Psychoduster said:
Ok.....

did some research and the base plate I'm looking for is from a Holley 5402010GC 750 Mighty Demon.
Thought here are some carb cracks arround :D, but if someone has the same problem.... that is the solution.

Regards, Eckhard
Click to expand...
Hey. Sorry I didn't see this earlier. There should be no connection between any fuel passages and the throttle shafts. If you see fuel there, it is not the throttle plate unless there was a porosity problem or crack.
Possible it is dripping from the boosters - that would suggest fuel level in the bowls is too high.
If not, look for other traces of where its coming from. Might just try a fresh set of good gaskets.
 
Mattax said:
Hey. Sorry I didn't see this earlier. There should be no connection between any fuel passages and the throttle shafts. If you see fuel there, it is not the throttle plate unless there was a porosity problem or crack.
Possible it is dripping from the boosters - that would suggest fuel level in the bowls is too high.
If not, look for other traces of where its coming from. Might just try a fresh set of good gaskets.
Click to expand...
Hi,

thank you!
And this was the first thing I did - new gaskets and fuel Level.
After I changed a few gaskets (nearly everything) I did a short "off engine test".
I gave the carburetor fuel from a pressure free source and let the bowls fill.
I opened the throttle to see if the squirter nozzles are free and I noticed the fuel coming out of the accelerator pump is leaking at the throttle shaft.
I did the same procedure, after I installed the carb back again (fuel pressure 6,5-7 psi).
Same problem (with engine running)
So the Problem are the shaft bushings..... but as the whole base plate has seen better days, I want to replace it.

I am still searchin for the needed part, because I can't find a spare part # for the base plate....
And as I wrote above (and you can see or read) I live in Germany and we don't have much Shops for US-cars (and the ones, that exist have a criminal pricing strategy) :)

Anyway my Duster is in hibernation.... the carb has to be fixed till march
.... winter is coming and fortunately I have a DODGE RAM 1500 as daily drive.

Perhaps someone has a good onlineshop for me?

Regards, Eckhard :popcorn:
 
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Okay, let me help you understand what is happening. I build these carbs, have 6 in stock right now. ALL BG's have loose throttle shafts compared to a Holley. Having a loose throttle shaft DOES NOT make a fuel leak; it DOES make a vacuum leak. Don't believe me? Think about this: When the engine is running it creates a vacuum under the throttle blades. When the shafts have play (which they all do unless bushed) un-metered air will be drawn around them. You may get a whistle at certain throttle openings, or it may have trouble returning to idle without a strong return spring.

Now, the fact that you have fuel pudding and running down the shafts is the real issue and is not being addressed. Why are your booster dripping? Mostly likely the float level is too high OR a bad needle & seat. Try lowering the float levels. You have sight glasses. Is the fuel level with the engine running in the middle of the glass? It should be. Is the car very rich at idle? Can you see fuel dripping out the boosters with it idling? Slowly open the throttle as you look down the carb neck.

Good luck.
 
Hi Mopar-Man,

o.k. perhaps my description was not good enough.
The Boosters are not dripping.
When I hit the throttle, the fuel from the accelerator pumps goes downward the carb and not all of it is sucked into to engine.
A small ammount is dripping out of the carb, between the shaft and the plate.
This only happens, if I hit the throttle a little bit harder. If I press the pedal realy slow, there is no dripping.

Fuel level is set to the middle of the window at idle Speed.

I will check the idle mixture and needle & seat......

Thank you for the reply, regards, Eckhard :)
 
Psychoduster said:
Hi Mopar-Man,

o.k. perhaps my description was not good enough.
The Boosters are not dripping.
When I hit the throttle, the fuel from the accelerator pumps goes downward the carb and not all of it is sucked into to engine.
A small ammount is dripping out of the carb, between the shaft and the plate.
This only happens, if I hit the throttle a little bit harder. If I press the pedal realy slow, there is no dripping.

Fuel level is set to the middle of the window at idle Speed.

I will check the idle mixture and needle & seat......

Thank you for the reply, regards, Eckhard :)
Click to expand...

O.K. So its definately not the throttle shafts. When the engine is running, that fuel should be pulled to the lowest pressure - the cylinders.

When the fuel comes out the accelerator pump, it should be when the throttles are opening. If you suddenly close the throttle, or the engine is not running. Then yes some of it may end up on the throttles and spread from there.

PS
6.5 psi should be OK, but it is about the maximum the float and needles can hold. If you can run less pressure, that is better.
 
Honestly. I think your description was good. Really don't think a video would change what we've posted.
 
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