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Historical - Fuel Metering in SI Engines #5348925 02/13/20 11:24 AM
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MolaKule Offline OP
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Before the advent of fuel injection systems various carburetor designs were used.

For V8's, the carbs of choice were either the Rochester 2-Barrel or the QuadaraJet 4-Barrel.

In the QuadaraJet,carburetor there was a small piston assembly sitting in a fuel well.

Q1: What was the name of this small piston assembly?

Q2; What was it's function with respect to the metering rods?


This question is NOT open to any Engineering Discipline.


Remember, your response goes into a queue so there will be a delay in the appearance of your response.

Last edited by MolaKule; 02/13/20 11:27 AM.

Charlie Eppes: "Larry, have a minute?"
Dr. Larry Fleinhardt: "Yes. Because we all have exactly the same number of minutes at all times, do we not?" From NUMB3RS
Re: Historical - Fuel Metering in SI Engines [Re: MolaKule] #5348936 02/13/20 11:38 AM
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BigGee Offline
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I always called it the power valve ,it lifted metering rods to richen the mixture at part throttle.The secondary top butterfly lifted the rods when the secondaries were opened.

Re: Historical - Fuel Metering in SI Engines [Re: MolaKule] #5348942 02/13/20 11:46 AM
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Accelerator pump. Augment fuel flow during increased throttle opening where otherwise fuel/air ratio would go too lean for smooth engine operation.


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Re: Historical - Fuel Metering in SI Engines [Re: MolaKule] #5348954 02/13/20 11:59 AM
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We called it an accelerator pump. It squirts extra fuel in when the metering rods are raised to give the fuel time to catch up with the extra air when the secondaries are actuated. To help with the fuel delivery delay.


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Re: Historical - Fuel Metering in SI Engines [Re: MolaKule] #5348961 02/13/20 12:11 PM
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It's the accelerator pump. (or that is how I learned it).
It squirts gas into the engine when you step on the gas pedal. Without it, the engine would hesitate when you step on the gas.


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Re: Historical - Fuel Metering in SI Engines [Re: MolaKule] #5348981 02/13/20 12:35 PM
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old1 Offline
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I think Big Gee had it right


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Re: Historical - Fuel Metering in SI Engines [Re: MolaKule] #5349018 02/13/20 01:28 PM
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As others stated, accelerator pump. Gives fuel as the air flow increases so fast when the secondaries open, prevents a lag when they open. Holley had a double pumper carb with 2 pistons.

The quadrajet spreadbore, when right really got decent mileage and ran well. I've rebuilt a few, but its been a while. Not everyone could get them right.


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Re: Historical - Fuel Metering in SI Engines [Re: MolaKule] #5349044 02/13/20 02:34 PM
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ragtoplvr Offline
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The small piston sitting in a fuel filled well is called the accelerator pump.
The small piston sitting in the middle of the fuel bowl is the power piston.

your question is unclear. Hence 2 answers.

Re: Historical - Fuel Metering in SI Engines [Re: MolaKule] #5349104 02/13/20 03:38 PM
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MolaKule Offline OP
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Looks like a Hint is in order:

This device prevents oscillation of the metering rods.


Charlie Eppes: "Larry, have a minute?"
Dr. Larry Fleinhardt: "Yes. Because we all have exactly the same number of minutes at all times, do we not?" From NUMB3RS
Re: Historical - Fuel Metering in SI Engines [Re: MolaKule] #5349128 02/13/20 04:02 PM
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There is a metering rod spring that prevents movement of the rods relative to the hanger in the primary power piston. Having rebuilt a lot of Qjets in the day, there is nothing to prevent the primary power valve piston from oscillating except the mass of the piston and the size of the passage feeding it vacuum. Well that and occasionally varnish from fuel builds up there. I never noted excess wear of the piston or bore, so it must not oscillate significantly.

Rod

Re: Historical - Fuel Metering in SI Engines [Re: MolaKule] #5349951 02/14/20 01:17 PM
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BigGee Offline
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Power piston assembly is the correct name that I have found on a diagram today.

Re: Historical - Fuel Metering in SI Engines [Re: MolaKule] #5351907 02/16/20 03:54 PM
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MolaKule Offline OP
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Thanks for the many responses and I too have rebuilt quite a few Quadrajets myself for older Suburbans.

According to E. Obert in, Internal Combustion Engines and Air Pollution,, Section 11-10 where he describes Carburetors for High Output Engines and specifically he discusses the Quadarjet he says, "To prevent wavering and oscillations of the metering rods, a dashpot, a piston in a fuel well arrangement, is included."

I would have preferred the term damper.

Now the closest thing I could find to what is described as a dashpot assembly is Part 15 in the exploded view below for the 4MV of 1966..

https://quadrajetparts.com/-a-7.html

Last edited by MolaKule; 02/17/20 02:24 PM.

Charlie Eppes: "Larry, have a minute?"
Dr. Larry Fleinhardt: "Yes. Because we all have exactly the same number of minutes at all times, do we not?" From NUMB3RS
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