Carter Mechanical Fuel Pump?

[brian6pac]

i know that the carter 6903 was mopar performance supplied pump for street/strip as well . that the one i just installed on a mild 340 . it gets my vote . the 4862 is to much pressure for the thermo carbs . and for most street carbs as well .

The M6903 is a big block pump

 

[pomonamissel]

sorry about the part #'s just used the #'s given . my pump was a m6270 . its the same series as the 6903 as far as pump volume and pressures , as well as fittings used .

 

[pomonamissel]

my mw ran two 660 holleys . i never had a pressure issue , but we did use the holley fuel pressure regulator in line from the electric pumps , and used it to split the fuel to the carbs . i think @ 5 psi would be enough . i used the gross jet ball needle seat set up , never had an issue with them . in my holleys at high pressures .

 

[SSing]

How much if any, can you adjust the psi on one of these Carter Mechanical Fuel Pumps?

 

[pomonamissel]

never tired on the pump itself . just used a external psi reg .

 

[SSing]

my mw ran two 660 holleys . i never had a pressure issue , but we did use the holley fuel pressure regulator in line from the electric pumps , and used it to split the fuel to the carbs . i think @ 5 psi would be enough . i used the gross jet ball needle seat set up , never had an issue with them . in my holleys at high pressures .

Ok, well the thing is I want to run this thing like they did back in the days. No fp regulator...

 

[pomonamissel]

well its all about the needles and sets . not sure if there is good ones that can hold the psi back . i know the gross jet ball set did . your set up was a stock package , there has got to be some members running there as they came . holley made a mech fuel pump as well . might it be the answer to the issue ? that pump had 1/4'' pipe threads also i believe . holley owns everything aftermarket , maybe there still servicing that pump too . i had run them with my holleys back when with on issues .

 

[SSing]

well its all about the needles and sets . not sure if there is good ones that can hold the psi back . i know the gross jet ball set did . your set up was a stock package , there has got to be some members running there as they came . holley made a mech fuel pump as well . might it be the answer to the issue ? that pump had 1/4'' pipe threads also i believe . holley owns everything aftermarket , maybe there still servicing that pump too . i had run them with my holleys back when with on issues .

Thanks for you input
No it has to be all SS/B (carter), so I´ll try the 4862. This was used in the mid 70`s after the 4024. The 4862 is a 4024 with 1/4" pipes... right? No way I want to use a fp regulator. There must be a way to lower the psi on the fuel pump, If I need to...

 

[pomonamissel]

well every pump has a relief spring for the check ball , less spring , less psi . just like an oil pump right .

 

[SSing]

Yes, one more thing than...
Anyone who have tampered with these Pumps, to change PSI? I´m thinking of the spring on the pressure side?
Or maybe a rebuild kit from a pump working with less PSI?
And no, no regulator in this engine bay...

 

[Mattax]

The answer to your question about rating is yes. Your shop manual will have a free flow test based on a low rpm and stock resistance on the suction line. The aftermarket usually uses free flow and whatever rpm they feel like. It's almost useless. What is needed is a graph of flow for rpm at a pressure that represents a nearly open needle and seat (or two or three).
Some circle track guys will go through the trouble of testing.

A diaphram type pump, as these all are, uses inlet and outlet check valves. The Carter and Holley check valves are little flappers (spring loaded). Volume per stroke depends on the diaphram size, the number of valves. Flow depends on the volume per rpm. The spring returns the diaphram. Enough pressure prevents the return and provides regulation.

Catherder explains it better than I. See
racingfuelsystems.myfunforum.org - View topic - Daytona's 'improved' Inlet Needle & Seat?
Follow the link to the Studebaker Carter 3508 thread for inside pictures of this type of pump.

 

[SSing]

The answer to your question about rating is yes. Your shop manual will have a free flow test based on a low rpm and stock resistance on the suction line. The aftermarket usually uses free flow and whatever rpm they feel like. It's almost useless. What is needed is a graph of flow for rpm at a pressure that represents a nearly open needle and seat (or two or three).
Some circle track guys will go through the trouble of testing.

A diaphram type pump, as these all are, uses inlet and outlet check valves. The Carter and Holley check valves are little flappers (spring loaded). Volume per stroke depends on the diaphram size, the number of valves. Flow depends on the volume per rpm. The spring returns the diaphram. Enough pressure prevents the return and provides regulation.

Catherder explains it better than I. See
racingfuelsystems.myfunforum.org - View topic - Daytona's 'improved' Inlet Needle & Seat?
Follow the link to the Studebaker Carter 3508 thread for inside pictures of this type of pump.

Thank you Mattax. Interesting reading, not just for me I´m sure.

As for the pump, I´m going to chose the 6903 model, witch is rated at a lower PSI than the 4862...
On the manciniracing website you can read about the 6903 - 02 pump... "These Super Mechanical Fuel Pumps are available exclusively from Mancini Racing"
But the 6903 you can found on several places on e-bay. Have Mancini added some tricks to their pump? I suppose and hope all the 6903 pumps are all the same...