accelerator pump Q..

[hardtimes]

Some carbs came without such pumps and later carbs with.
What is your opinion/experience when using a carb without a working pump. What would you expect engine performance to be, other than acceleration provided by pump ?

[Ronnieroadster]

Originally Posted by hardtimes

Some carbs came without such pumps and later carbs with.
What is your opinion/experience when using a carb without a working pump. What would you expect engine performance to be, other than acceleration provided by pump ?

With a single carb having no accelerator pump there will be a huge off idol stumble making it near impossible to drive the vehicle. Any attempt to try and gain acceleration without the pump enrichment will be meet by a much bigger stumble.

[oldford2]

Originally Posted by hardtimes

Some carbs came without such pumps and later carbs with.
What is your opinion/experience when using a carb without a working pump. What would you expect engine performance to be, other than acceleration provided by pump ?

Now, this Fordbarn.. What carbs came with no accelerator pump for 32-53 flatheads???????????

[cmbrucew]

Changler groves ?
Bruce

[hardtimes]

Originally Posted by oldford2

Now, this Fordbarn.. What carbs came with no accelerator pump for 32-53 flatheads???????????

Well, since about any carb can be used on a flathead, I'll start with Winfield Model S. There were others , but how does this answer the question ?

[hardtimes]

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Originally Posted by Ronnieroadster

With a single carb having no accelerator pump there will be a huge off idol stumble making it near impossible to drive the vehicle. Any attempt to try and gain acceleration without the pump enrichment will be meet by a much bigger stumble.

Hey Ronnie,
So, in such case, use of a choke would gain no improvement ? How about timing, as in would some advance not gain improvement either ?

[hardtimes]

Originally Posted by cmbrucew

Changler groves ?
Bruce

Hey Bruce,
Will have to check Chandler groves out, thanks.

[flatjack9]

Chandler Groves has an accelerator pump.

[Ronnieroadster]

Originally Posted by hardtimes

Hey Ronnie,
So, in such case, use of a choke would gain no improvement ? How about timing, as in would some advance not gain improvement either ?

A choke working correctly will reduce air into the carb allowing A richer mixture and also raise the curb idel at the same time if the linkage is adjusted correctly. Without the air the choke has reduced the engine will have a hard time performing correctly. Additional advance at times will help gain performance but only if the fuel mixture is rich enough to reduce pre ignition. No benefits can be gained with those two ideas.
The only two barrel carbs I know of without accelerator pumps are the secondary carbs used on factory tri power assembly's. Those factory systems work extremely well but all three carbs are designed for the purpose.

[hardtimes]

Originally Posted by Ronnieroadster

A choke working correctly will reduce air into the carb allowing A richer mixture and also raise the curb idel at the same time if the linkage is adjusted correctly. Without the air the choke has reduced the engine will have a hard time performing correctly. Additional advance at times will help gain performance but only if the fuel mixture is rich enough to reduce pre ignition. No benefits can be gained with those two ideas.
The only two barrel carbs I know of without accelerator pumps are the secondary carbs used on factory tri power assembly's. Those factory systems work extremely well but all three carbs are designed for the purpose.

Hey Ronnie,
Thanks for this information and ideas. So, multiple carbs make a difference, more so than a single ?

[scicala]

"The only two barrel carbs I know of without accelerator pumps are the secondary carbs used on factory tri power assembly's. Those factory systems work extremely well but all three carbs are designed for the purpose."


The only factory tri powers that I'm aware of without accel pumps in the end carbs were the 427 Corvette and 440/340 Mopars, and that was because the end carbs were opened with vacuum and not mechanically so they didn't open instantly. Even the original GTO set ups had vacuum controlled end carbs and still had accel pumps.

Sal

[hardtimes]

Originally Posted by scicala

"The only two barrel carbs I know of without accelerator pumps are the secondary carbs used on factory tri power assembly's. Those factory systems work extremely well but all three carbs are designed for the purpose."


The only factory tri powers that I'm aware of without accel pumps in the end carbs were the 427 Corvette and 440/340 Mopars, and that was because the end carbs were opened with vacuum and not mechanically so they didn't open instantly. Even the original GTO set ups had vacuum controlled end carbs and still had accel pumps.

Sal

Sal, thanks !
So, I get from Ronnie/Sal that a carb where the accelerator pump is not working and/or does not have such pump...is far from ideal for engine operation.
Still looking at how 'they' did without accelerator pumps back before they were recognized as necessary for better engine performance.

[scooder]

Usually with very small (for the engine) carbs that ran rich off idle, suffered flat spots, couldn't pull a greased stick out of a pigs arse, bunch of rubbish really and the reason proper carbs have an accelerator pump and a power valve.
Martin.

[RalphG]

Something to consider, my older gas tractors have updraft carburetors with no accelerator pumps at all. Yet they seem to function just fine. Are they over fueled to compensate? Off idle performance seems fine right up to their governed rpm of roughly 1700 rpm.
On my 52 Merc with the Holley teapot carb, the accelerator pump is weak and I have had to develop a driving style to compensate. I don't just step on the gas to take off, I "pump" the pedal 2 or 3 times and away it goes.

[scicala]

As far as I know, all automotive carbs have always had accel pumps either mechanically operated or by vacuum drop when the throttle is opened. Possible that real early stuff didn't (before 1930's).
A lot of industrial and commercial small engines didn't use them. I mean really small engines like Briggs and Stratton, etc.

Sal

[FRANK PKNY]

OK what's the difference between a power valve and an accelerator pump? On the early v8 carbs it's called a power valve. I think it just sends a richer mixture to the manifold, by changing the porting?

[ford38v8]

Originally Posted by FRANK PKNY

OK what's the difference between a power valve and an accelerator pump? On the early v8 carbs it's called a power valve. I think it just sends a richer mixture to the manifold, by changing the porting?

They are two different fuel systems. Three altogether in a Ford-Holley '94.
Power valve opens a system and stays open during the duration of a low vacuum period. Accelerator pump is a single squirt of fuel each time you stomp on the gas pedal. Th third system is controlled by the two screws at the back of the carb, which regulates the amount of fuel delivered to the venturi at idle speed. This system continues as long as the engine is running. Back to the second channel, where the accelerator pump delivers to, are the two nozzles at the top of the air horn, which suck fuel through the main jets in direct relation to the volume of air going through the air horn.

[hardtimes]

Originally Posted by RalphG

Something to consider, my older gas tractors have updraft carburetors with no accelerator pumps at all. Yet they seem to function just fine. Are they over fueled to compensate? Off idle performance seems fine right up to their governed rpm of roughly 1700 rpm.
On my 52 Merc with the Holley teapot carb, the accelerator pump is weak and I have had to develop a driving style to compensate. I don't just step on the gas to take off, I "pump" the pedal 2 or 3 times and away it goes.

'Are they over-fueled to compensate?'
This makes me think that you are onto something here.
I mean that the shape, design and size of things....were made( circa '30s) too fulfill the idea of necessary enrichment without 'complicating' carb/system (accel pumps perse).
For example, even the shape/size of the holes/ tube(s) in the carb throat could/were changed as 'compensation' over-fueling was needed.

[hardtimes]

Originally Posted by ford38v8

They are two different fuel systems. Three altogether in a Ford-Holley '94.
Power valve opens a system and stays open during the duration of a low vacuum period. Accelerator pump is a single squirt of fuel each time you stomp on the gas pedal. Th third system is controlled by the two screws at the back of the carb, which regulates the amount of fuel delivered to the venturi at idle speed. This system continues as long as the engine is running. Back to the second channel, where the accelerator pump delivers to, are the two nozzles at the top of the air horn, which suck fuel through the main jets in direct relation to the volume of air going through the air horn.

Alan,
Nice explanation !
Even today, guys change power valves/disconnect power valves and disconnect accelerator pumps and change orifice sizes to tune either single and more often multiple carb set-ups , to change / compensate for fuel flow for best work (street,track or strip) I think that the great engineers back when thought of same problems / solutions and approached them with different tech/ideas/conditions faced then

I'm now thinking that the answer that I was asking about...the design of carbs were job specific designed and if wanted to use for more than one job, i.e.- racing and/or street use , some form of enhanced enrichment had to be thought out ?

[flatjack9]

Originally Posted by ford38v8

They are two different fuel systems. Three altogether in a Ford-Holley '94.
Power valve opens a system and stays open during the duration of a low vacuum period. Accelerator pump is a single squirt of fuel each time you stomp on the gas pedal. Th third system is controlled by the two screws at the back of the carb, which regulates the amount of fuel delivered to the venturi at idle speed. This system continues as long as the engine is running. Back to the second channel, where the accelerator pump delivers to, are the two nozzles at the top of the air horn, which suck fuel through the main jets in direct relation to the volume of air going through the air horn.

The accelerator pump gets it's fuel directly from the float bowl independent of the jets.