Fuel pump 3 psi at idle
 

Hi All
Any advice would be great. I’m trying to dial in my carb. 850 SS quick fuels. On a 427 bb.

I have a mechanical pump that I clocked so I could hook up my fuel lines.

Earlier today day I had 5 psi on the Guage then it dropped to 4 then 3. I can’t figure out what’s up.
Needless to say I can’t dial in the carb on 3 psi. It calls for 6.5.i have a pressure regulator in line too. Maybe that plays into it. I have it cranked down all the way. It’s rated to 9 psi.

Seems like the motor is starving for fuel. I have to pump it 2/3 times and hold it to the floor!

Anyone have any insight?

Is the pump compromised because I clocked it?

Re: Fuel pump 3 psi at idle
 

I will start off with Yes I am a rookie. 100 percent super green.

Just learned about liquid filled fuel pressure gauges and what happens to them when they heat up. They drop like a rock. Nice.

So so that answers the pressure drop mystery.

But next question - will fuel pressure increase as motor gets warmer?

Re: Fuel pump 3 psi at idle
 

Unfortunately, not a lot if 1st Gen owners on the site any more. Sometimes we get lucky and someone pops in and helps out.

A long time since I had a car with a carb and a mechanical fuel pump, most of my experience is with high pressure EFI systems using an electric pump in or near the tank. But I'll give it a try.

Could you describe your fuel system in more detail? I believe in your earlier post you indicated you have a 3/8” fuel (suction) line from the tank to the mechanical pump. What size is the pump discharge line, and is that where you placed the fuel pressure regulator? Do you have the make and model number for the fuel pressure regulator (FPR)? I believe earlier you asked about adding a return line. Is the FPR a bypass type, or self regulating inline type? Do you have a filter on either side of the pump? Is the FPR “adjustable”? Have you checked the pressure without the FPR in the system?

Re: Fuel pump 3 psi at idle
 

Hi Fred -

I have a 3/8" stainless delivery line that goes to the mechanical pump. then braided stainless to the carb. I eliminated the pressure regulator now because the pump gives me the 6/6.5 I need for the carb. I do have a filter right after the pump on the way to the carb. pressure now Seems right on. So I have a better pressure gauge coming - one that heat won't effect - this way I know for sure.

But now my next gremlin (one at a time) is the fuel line on the frame rail is 2" away from the header and that line gets hot. Is there a fuel line sock that can handle the heat? should I re-route the line? Not much room to do so..

I'm gaining on this - thanks for the help!

Brian

Re: Fuel pump 3 psi at idle
 

Something like this will work. Good for up to 800-degF, wraps and seals with hook & loop (velcro) so you do not have to unhook the line to wrap it.

https://designengineering.com/heat-shroud-gold/


If you are close to the header primaries, the 800-degF spec above would be best. If you are further downstream on the exhaust system, you could use the lower temp, lower cost product:

https://designengineering.com/heat-shroud/

Those are Design Engineering retail prices, you could probably find them at a discount. Amazon has it.

If you continue to have problems with vapor lock, the next step would be to look at the diameter of the line from the tank to the pump. At very high flows required to support a high HP engine, if there is excessive pressure drop in the suction line, the fuel can flash to vapor. I run a 3/8" (-6AN) supply line for 800 HP, but I'm using dual electric pumps at the tank, so my line is on the discharge pressure side of the pumps (58 PSI), One pump is mounted outboard of the tank, capable of supporting 500 HP, and even with the short suction line between the tank and the pump, we used a 5/8" (-10AN) braided SS line.

Re: Fuel pump 3 psi at idle
 

Thx Fred

just ordered some heat shield from them. I’m sure it will help.