Fuel pump pressure?

[Talkwrench]

After fitting the slingshot manifold Ive jumped up by a good 1\2 lb . So now 3 1\2 lbs Must be a slight difference in height of the manifold. I was just going to put a thicker gasket under the pump stand but remember reading that it can also adjust volume flow, am I reading into this to much and knocking say 1 lb of with a thicker gasket won't hurt anything?

 

[Jack E/NJ]

Experiment. Jack E/NJ

 

[slowforty]

Also check the amount of flow from the pump. Should be able to flow about a pint in 15 seconds into a can.

 

[flatjack9]

I'd suspect the gauge.

 

[Phil Gillespie]

The above answers assist ie check flow as advised. I recently checked my fuel pressure from the mechanical pump. Removed fuel line to carb and fitted a pressure gauge. On crank over got 1.5 psi which i consideredto be ok. Did not measure flow volume. maybe the gauge?
Phil NZ

 

[flatheadmurre]

Fuelpressure is set by the springpressure so height of pump on intake should only affect flow not pressure...

 

[Jack E/NJ]

I don't think spring pressure is a linear response. Take it to the extreme where the push rod is just touching the pump a little bit. Little pressure, little volume. Jack E/NJ

 

[flatheadmurre]

I don't think spring pressure is a linear response. Take it to the extreme where the push rod is just touching the pump a little bit. Little pressure, little volume. Jack E/NJ

Within the limit of travel set by diaphragm it shouldn´t be a huge difference...spring is preloaded from start.
The design should aim for a constant pressure not pulsating...just my thinking.

 

[Jack E/NJ]

Yes, you're right, preloading in a near-linear response region sounds reasonable. Jack E/NJ

 

[G.M.]

I like 4 lbs COLD. Take the temp of the pump with a pressure gauge
in the fuel from the pump to carb this will give you the TRUE story.
The hotter the pump gets the more the pressure drops. If it gets hot
enough you will see vapor lock start to form by the fluxuation of
the pressure. G.M.

 

[Talkwrench]

Fuelpressure is set by the springpressure so height of pump on intake should only affect flow not pressure...

So why did it jump a good 1/2 lb when all I did was change manifolds?

 

[alanwoodieman]

height of the manifold boss for fuel pump, thinner intake gasket, both would yield more pressure. I will vote for manifold boss height.

 

[Phil Gillespie]

http://www.reds-headers.com/html/red_s_engine_talk_10.html

This info gives a few details concerning Fuel Pressure for the flathead as recommended at 3.5 psi. So from that looks like I need to check mine out as at 1.5psi seems a little low. Fitted with an 8 7/8" fuel pump rod. How much wear down before output volume and pressure are affected?
Phil NZ

 

[flatheadmurre]

So why did it jump a good 1/2 lb when all I did was change manifolds?

That´s a good question...have been thinking about it.
May it be that on idle you use very little travel of the spring between each time it´s compressed by the pushrod and that intake height affects it...would be interesting to see what average pressure you have running it under load when using more volume.

 

[Lawrie]

the length of the push rod will control the volume and the spring under the diaphragm will control the pressure ,in the service bulletins there is a length and poundage for the different models.
Lawrie

 

[Talkwrench]

I think I'll just try a thicker gasket and see, I doubt I have any problems with volume as I had a float failure on the weekend and just on cranking it fair pissed fuel out everywhere! I'll update when done.

 

[189j40]

had same problem. 2 extra gaskets under pump tower done!

 

[Talkwrench]

Well I did the gasket. I measured the one I took off at .022 but The only gasket material I had measured .029 (or .060 ) so went with that as I thought doubling it might be too much. Didnt do much , slight difference now just over 3 lb so I'll kick on with that for a bit.

 

[SofaKing]

The .022 was compressed, I am curious what the .029 material will measure after it is compressed. What changes were part of the upgrade, fuel lines, number, length, diameter, etc? Please update this thread if you have further developments.

 

[Talkwrench]

Really no other changes, the line length from the pump is a little longer for the added height, tiny bit extra of 5 /16 hose.. Did have to remove some of the bottom of the pump as it was touching the manifold..