Ford V8 Flathead Fuel Pump

OK, I read that a stock Flathead fuel pump pressure can be reduced by shortening the pump rod, not so much that it won't work??????????
True or False...
Duane..

 

Never heard of. Just a thought, would that drop the pressure or volume? I am guessing the latter.

Neal

 

Shortening the pump or adding gaskets under the stand will drop pressure but also volume, and I suspect will reduce available vac for the thing to self prime.
Apparently most current manufacture flathead pumps come with diaphragm springs (the part you really want controlling the pressure) from some later model pump and are too high, some as high as 7 pounds.
Unscrew the lid and install the spring from the oldest and dirtiest flathead pump in your junk bin.

 

I read about the gaskets. I just bought a new offy manifold and it seemed it was a quarter inch shorter than the stock manifold. I cut the rod a quarter inch and now it doesnt pump. Im getting a new rod and will try adding gaskets till it works good. I also read that if the rod is off by just a little that it wont work right, or at all.

 

Measure the distance from lower gasket surface of manifold and gasket surface where pump stand mounts; you don't say what engine you have, but there is only one height for '49-53 engines and that height plus one 1" shorter for various pre-49 applications.
Compare that with your stock manifold. I don't have numbers without measuring some manifolds, but the long-rod ones will be around 2" and short about 1". If you have a late engine or almost any iron early manifold, correct will match that, if you have one of the low manifolds it'll be 1" shorter exactly.
A late offy should match the long. I think early Offy's use the higher platform too, but not 100% sure without looking in the manifold bin.
You want full available rod length for your application, since lobe travel is only like .2 or so. If a new manifold is manufactured fubar, I'd return it. If you want to jury rig, measure a stock manifold and shorten the rod by no more than the manufacturing error in the manifold. Stock gasket under pump stand is thin stuff...either a fat gasket or a warped pump stand flange can kill most of your travel.

 

Great info Bruce..Now, if I don't have and old spring, what is the proper way to weaken the spring, using heat and cooling or what...Any help how to do this..
Thanks
Duane..
ps..can the spring be shortened???????Not so many coils????????

 

I would use a pressure regulator instad of modifying springs. modifying the springs could lead to failure of the spring=no fuel. And you know it will happen the furthest away from home you ever got in the dark in the rain.

 

why do you need to reduce the fuel pressure.the needle and seat should be able to handle 5 to 6 psi.

 

Well, I have someone that doesn't want any guages..5 to 6 psi is to much for a Stromberg 97..
Thanks
Duane..

 

Where is Continental John?? He manufactures springs...he can surely give advice on reducing spring rate, but isn't this a product possibility?? Fuel pumps in general are becoming a flathead problem. Everything new seems to have wrong spring.

 

If you remove coils the spring rate will go up not down. Add coils and it drops because the range were the spring is working in is lower. Also reduce the wire size and increase the diameter. Don't heat her up . Please give me some specs and I'll make you some to try Thanks

 

Thanks Bruce and more than happy to help. What kind of fuel pumps are we talking about?Please give me some spring dimensions and I'll twist some up for ya Also the new 97 carbs and fuel inlet replacement have a ball check and that needs to be looked at. I have not put a force gauge to one but should to see were its at, Thanks

 

CJ...these pumps are the same construction as about any engine driven pump from the '50's and '60's, up til they went to crimped and sealed construction, but very low pressure, 1 1/2-3 pounds output spec.
I'm at work and don't really know how much info I can beat out of the books (Ford didn't need to provide that much info on a readily available 10 cent part!) but...
The diaphragm spring spec that I can find is for 7.10--8.6 pounds spring pressure at .625 compressed height.
I think most late pumps put out 6-7 pounds pressure, and I suspect that the springs from those are going into current flathead pumps.

 

Transmission guy Van Pelt has the Ford exploded view online:

http://www.vanpeltsales.com/FH_web/FH_images/FH_fuelsystem-pics/Flathead_Engine_fuelpump1947to48.jpg

9396, the root call number, is the piece...I think diameter is pretty well fixed by the cup areas that hold it in casting and under the diaphragm. Most small size AC type pumps used maybe 1935--1967 use a closely similar spring, but with wide range of spring rates...so spring rates most readily available to rebuilders/builders are from applications involving carbs with much greater pressure tolerance than a Stromberg. I understand you can buy brand new flathead pumps from Carter and such that come in at about twice the early Ford spec!

 

Bruce, If you have a spring that's the right one, measure the wire diameter and the lenght of the wire. That's what CJ needs to figure the spring rate and make a new one of the right tension.

Frank

 

I am World Headquarters for filthy old flathead pumps.

 

And...anyone have any recently purchased new flathead pumps that could have a bit of vacation time to go visit Continental John? We need some numbers to go with the anecdotal evidence.

 

I grab one out of the cellar and will take her apart in the morning. So who wants to give it a go I'll have specs and what range do I shoot for 5lbs @.625 ?

 

I'd go for about the LOW end of the spec above. That spec is for the originals, not the current repro ones. Bruce

 

I have two 97's and run them at 2 lbs. with a pressure regulator(recomened). It runs great.

 

Found some numbers...40-9396 diaphragm spring used on most '34-48 flathead pumps.

All I have:

7.10--8.6 pounds pressure at 0.625 test length...1 1/2-3 1/4 pounds output pressure spec on the common later pumps.

 

dont do it,insytead if u need to reduce pressure get an in line adjustable regulator.I have used stock pumps on my flathead for years,have had 3 deuces,one deuce and now 2 deuces and there is no problem with the stock pump.flatheads florever

 

Is there anyway to increase the pressure? I am using the stock pump on an early flathead ('39) with two Strombergs. I have an inline gauge and it's only reading 1-1 1/2 lbs. Is this pressure ok? I haven't driven the car yet, this is only tune up in the driveway so far.

 

You are fine. Chill.

 

Thank you Bruce, I feel better already.

 

Quick and easiest method....Go with a pressure regulator..... 3 PSI for Strombergs...New as well as old ones.....

4TTRUK

 

God I love this place............!

 

I'm sorry to drag this up again. But, we're restoring a historic Roadster to match the photos of it in old magazines. This car didn't run a fuel regulator or a fuel pressure gauge as shown in the pictures. We want to keep the car authentic to match the early photos, so adding a fuel pump regulator after the fuel pump is not an option. Since we can't use a regulator, we want to try and provide the correct pressure (and volume) with the stock fuel pump.
The car has two Stromberg 81's on an Evans intake. it uses a stock Ford 11A-9350 fuel pump (without glass bowl), stock fuel pump stand and a 7.87" fuel pump push rod. The goal is to get no more then 2.5-psi to the carbs to avoid flooding. I've read above about adding gaskets and cutting the push rod, but both ideas sacrifice volume. I've also read about replacing the diaphragm spring, this seems most promising. Can anyone share their experiences with modifying or substituting the diaphragm spring? I'm also open to other suggestions for modifying the fuel pump. Thank you!

 

I have been building hi po flatheads for 60 years. A new pump will put out 5-6 pounds. I don’t have enuf “space” between the pump and carbs(always more than 1 carb) to run a regulator so I put extra gaskets under the pump(usually 1/4 inch or so) to reduce the fuel pressure down to 1.75 or 2 pounds. Have NEVER run out of fuel and have run 2 engines on dyno runs(6 runs) and the car(32 ford cabriolethiboy) has run many times at the track—-has run 80 mph in the 1/8 with 3:89 locker and has never run out of fuel and I run my engines as hard as you can imagine. Flatheads Forever!!