Register now to get rid of these ads!

Technical mechanical fuel pump too much pressure

Discussion in 'Traditional Hot Rods' started by highpockets, Apr 15, 2017.

  1. 24riverview
    Joined: Jan 13, 2008
    Posts: 897


    My son volunteered to get my mother's 37 ready for a wedding late last year- post 46
    Fuel pump was leaking on the 305, he put a new pump on Friday night and had fuel pressure issues right away. He didn't have a way to check the pressure (I was already on my way to wedding) and no amount of attempted carb repair (Q jet) would cure it. Interesting part to me was this spacer you were suppose to install if pressure was to high. Anybody else ever heard of this before?
    Saturday morning he got a different pump from another supplier and the car purred like a kitten for around 5-600 miles that weekend.
  2. Blues4U
    Joined: Oct 1, 2015
    Posts: 5,092

    from So Cal

    I had 2 of them fail on me. The first one just started dribbling fuel, so I replaced it. Maybe 6 months later the new one failed, and when it failed it was squirting a steady stream of fuel. That's not a good situation to have a flammable liquid being squirted into a hot engine compartment. I replaced it with a Holly regulator and it's been working great ever since. The Holley regulator is a good quality part.
  3. Blues4U
    Joined: Oct 1, 2015
    Posts: 5,092

    from So Cal

    Not to argue, but just to clarify, pumps produce flow, not pressure. As 31 Coupe posted above, pressure is a result of resistance to flow. But yes, a pump like you described increases flow with increased RPM, and as that flow encounters resistance the pressure will increase.
    carbking likes this.
  4. Truck64
    Joined: Oct 18, 2015
    Posts: 4,235

    from Ioway

    Somebody here at the HAMB in fact mentioned stacking gaskets to reduce pressure output. I tried it without much success. Given the angle offset on the particular fuel pump I was messing with it seems like it should work. How thick is that spacer, maybe 1/4"?
  5. carbking
    Joined: Dec 20, 2008
    Posts: 2,927


    OK - will agree.

    However, if one tests a pump with the outflow blocked, then, assuming there is a bypass, a certain output pressure will result, which is basically controlled by the tension of the diaphragm spring in the pump.

    Since engines use the least amount of fuel at idle, the resistance to flow will be highest at idle, and the resultant pressure will be highest at idle.

    Truck64 and Blues4U like this.
  6. NAPA 68
    Joined: Dec 4, 2011
    Posts: 25

    NAPA 68

    This post here bailed me out. It's a great point that is not often pointed out. I was pulling my hair out on a 2100 Autolite that would flood out...........but not always
  7. JeffB2
    Joined: Dec 18, 2006
    Posts: 8,660

    from Phoenix,AZ

    Your issue comes up on a lot of forums since almost all pumps are now offshore made pressures are all over the place and causing problems,if you run a mechanical pump use a regulator like the Holley with a sight gauge those dial a pressure ones are junk.
    olscrounger likes this.

Share This Page

Register now to get rid of these ads!


Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.