what is normal working pressure for a mechanical fuel pump?

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fuzzman

fuzzman

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Hey all just wondered if it is normal for a carter mechanical fuel pump to drop down to 5-1/2 pounds pressure when it gets warm? When I first start the motor it runs at about 7 pounds and after it warms up it drops down to 5 to 5-1/2 to 6 it kind of bounces back and fourth around those pressures and sometimes lower. Is this normal? I have a 3/8 fuel line along with a 3/8 pick up. I had a holley pump that would start out at 8 pounds and would drop down like that when it got warm also. just curious if this is normal
Pat Faley
East Peoria IL
67 NB
69 convertible
Barracudas
 
My 318 runs at 7.5 if I don't regulate it. It is an OEM mechanical. I put a regulator on it to keep it below 6. Now it likes to sit at 5.5 all day. My Eddy does not like 6+, starts to flood at idle.
Probably doesn't help but wanted you to know where another mechanical was running.
 
it doesn't matter which RPM when it is cold and warming up it sits right at about 7 than as soon as it warms up it is running at 5 to 5-1/2 I would like to see it stay right at 6-1/2 but I have tried two different mechanical pumps and they both do the same thing. I have the original mechanical nonperformance pump that I haven't tried yet. I have insulated al the lines close to the headers and tried to make sure the line coming from the pump to the carb doesn't touch any heater hoses just don't understand why it drops when its warm.
Pat
 
I forgot o mention I'm running a quick fuel 750SS mechanical secondary's and it is suppose to have 6.5 fuel pressure. I had the holley mechanical installed and took it on a road trip about 100 miles each way an d the temps on the way home where around upper 80's so the car at the time was running a 195 thermostat so the car was running right at 195 and the pump at that time was running at 3 pounds when I pulled into my drive way so I guess what my dilemma is do I go with a electrical pump and do away with the mechanical because they don't seem to be doing the job. like I said in the last post I have insulated all the lines that I think are close to the headers and put a heat shield under the carb changed the thermostat to a 180 with little change other than I've seen now that it stays at 5 to 5.5. so totally baffled.
Pat
 
3 is not good, 5 to 5.5 is in prob not bad. The main question is does it maintain that pressure as you run it thru the gears at WOT. If it drops any more I would worry about the carb running out of fuel. The reason so many people like electric is they will maintain whatever pressure you set it at. I don't know the demands of your engine but if it maintains the 5 thru the gears and doesn't show any signs of sucking the carb dry you should be fine.
 
Lol my carter fuel pump runs 6psi-7psi and i believe the engine biulder said after 7 or 10 seconds at wide open throttle it dropped to around 3psi.
Whos gonna be on wide open throttle that long, especially when you shift rpms wil drop the pick back up. Maybe get there in a 1/4 but deff not in a 1/8 and deff not on the street
 
In 15 years Ive never measured my fuel pressure.IMO a fuel pressure gauge on a streeter,is just one more thing to worry about. Im glad I dont have one. Im also glad I dont have a fancy oil pressure gauge. Same reason.I dont have a fancy temp gauge either. Same reason.
When I get in the drivers seat, I just want to drive. I want to get sideways. I want to feel the power, and the rush;again and again.I want to hear the screaming tires, smell the burning rubber, see the tack-needle buried.
If it blows up, it blows up.
It hasnt yet.

I got no time for steenking worries.
Jus MO
 
I hate to sound stupid but I did find out by mistake that it is a good idea before you make the connection from your fuel main is to make sure that gas is running out like a siphon so that you know all the air is out of the line. The mechanical pump works much better when the fuel line has all the trapped air out of it. I think I have been fighting this issue for quite some time. Like I said I found this issue by mistake. I was going on the assumption that the sock inside the tank was clogged with junk so, I was trying to blow the line out and all of a sudden the gas started running back like a fountain so I hooked the pump back up and fired the motor back up and the pump was holding a steady 6.5 pounds. It was all because it was line locked with air. I would say a good rule of thumb would be make sure the main fuel line has all the air out of it before you hook it up to the suction side of the pump. Problem solved, DAH!!! thanks for all the replies
Pat
 
fuzzman
that is fuzzy logic.
If a mechanical pump(not necessarily yours) cannot self-prime it is ndg.That pump will suck air out just as fast as fuel, provided that the end of the line in the tank is clear. Either you blew a hole in the sock, or blew it off.It would probably be a good idea to check it, or at least put a new filter in the glove-box.I have a feeling you're gonna need it.
 
AJ
I have decided that you are correct with this being fuzzy logic I have looked into this further by pulling the filler tube out of the tank and decided that the tank needs to be dropped and drained because of flakes of stuff in the tank. which I'm sure is clogging up the sock inside the tank that's why I keep getting up and down pressures on my fuel system. It still runs fine when I drive, the pressure will start out at 6.5 than drop down as low as 3 psi than creep back up to around 6 and back and fourth. The problem I have right now is a full tank of gas and rainy weather so waiting for the sun to come out to get some windshield time. Thanks for the replies
Pat Faley
 
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