Fuel pump questions

James Boughton jpb01 at ibm.net
Wed Dec 10 20:19:07 GMT 1997


> The return line must have a min of pressure.
> All gas tanks have a line at the bottom of the tank, for the pick-up,
> and then various others, they can be mounted all over the place.  
> I beleive it was some Chry. where they had some mounted on the sides at
> about what would be 7/8 full.  On some tanks there is a large trapped
> air bubble, all I was making the point was not to let the return line be
> covered, if the return is sometimes covered the return line pressure
> goes up, the regulator can't bleed the pressure down, and the motor goes
> very rich.
>   Hope that better explains it   Bruce  nacelp at bright.net


Uhhh, no.  The pressure 1" below the surface of the fuel is not that much
different than the pressure 1" above the surface of the fuel.  In fact, a 6'
tall column of fuel should only change the return pressure by ~3 psi (this
may be considerable for a carb., but I haven't run into too many 6' tall
on board fuel tanks recently:-)).  Anyhow, unless there is some mysterious
flow phenomenon (or you run very low fuel pressures) where the return line
is should not make a difference.

Jim Boughton
jpb01 at ibm.net



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