<VV> Stock fuel pump pressure output

corvairduval at cox.net corvairduval at cox.net
Tue Jul 30 12:22:54 EDT 2013

The following concerns stock mechanical pumps:

The two valves in the pump are check valves to keet the fuel flowing
towards the carbs and not back to the tank. They are not relief valves, as
in relieving excessive pressure.

Fuel pressure can only develop if the needle and seat provide back pressure
to flow. So the highest fuel pressure is at idle, since more time with the
needle on the seat.

Maximum fuel pressure is determined by the spring constant of that big
heavy spring in the top of the pump pushing on the diaphragm.

Pressure is not rpm dependant (except as noted above the needle/seat
relationship at different rpm) as the throw of the fuel pump eccentric just
compresses the spring. The spring relaxing pushes on the diaphragm.

John Moody wrote a great article describing how a typical mechanical fuel
pump works.

Frank DuVal
Fredericksburg, VA

Original email:
From:  Sethracer at aol.com
Date: Tue, 30 Jul 2013 11:28:02 -0400 (EDT)
To: chsadek at comcast.net, virtualvairs at corvair.org
Subject: Re: <VV> Stock fuel pump pressure output

1965 factory Shop Manual - (Engine tune-up page 6-2) says 4-5 lbs. at idle  
(1000 RPM) One pint flow in 30-45 seconds. - Seth
In a message dated 7/30/2013 8:12:17 A.M. Pacific Daylight Time,  
chsadek at comcast.net writes:

What is  the design fuel pump pressure? Tolerances?  Is the pressure rpm  
dependent? Is there any data on the relief valves within the fuel  pump?


Chuck S
Fredericksburg, VA

myhosting.com - Premium Microsoft® Windows® and Linux web and application
hosting - http://link.myhosting.com/myhosting

More information about the VirtualVairs mailing list