Fuel System help

[69gmachine]

My engine was running too rich. Fuel pressure was 7.5psi at idle and the needle and seat assemblies were too large (130 windows). I had a modified Carter mechanical fuel pump with a larger than stock spring and valves, -8AN inlet and outlet. I ran 1/2" line with -8AN fittings from the fuel cell to the pump, and from the pump to a Summit G3131 pressure regulator. From there it teed off to the primary and secondary fuel bowls, still with -8AN lines. No matter what I did, I couldn't get the fuel pressure to go down, although it was supposed to be adjustable from 4.5 to 9 psi.

Since then I replaced the needles with 97s (also windows) and a regular street Carter pump. I retained the -8 fitting on the inlet so I could plumb it into the exisiting fuel lines. Now I need to get the fuel up to the carb. I was thinking of using a stock Boss 302 pump to carb line, but wonder if it is adequate to support close to 500hp (what I think I should be near with my combination). The -6 AN fittings seem to go with 3/8in line, and that is very common for pump to carb lines.

My goal for this car is to take it to open track events (hopefully in the not too distant future) so it won't be sustained running at 500hp anyway. I will also take it to the drags only because I live less than 20 miles from MIR. It is too radical to be a daily driver, but it will see street duty.

Any help from someone with a similar large carbed (around 400cu in) NA combination would be greatly appreciated.

 

[69gmachine]

Problem solved

Didn't get much sleep last night, but I decided how to proceed. This morning I disassembled the fuel pump and drilled and tapped the outlet for 3/8 NPT. Next I enlarged the hole at the back to the same size as the i.d. of a -8AN fitting. Then I installed a 3/8NPT to -8AN fitting in the outlet with teflon sealant. This seemed to be the obvious solution, allowing me to use all the existing fuel lines. After I get everything dialed in I may redesign the supply line to mimic the Boss 302/428 CJ layout by swapping front carb bowls. Anyway, I reinstalled the pump on the engine and re-connected the fuel lines. This will work for now. Still not sure how to adjust the regulator , but hopefully with the stock fuel pump it really isn't needed anyway. With the -8AN inlet and outlet I should have an HVLP fuel system.

 

[iskwezm]

to adjust the regulator,you turn the "set" screw on top in to raise and back it out to lower pressure.Your FP seems kinda high at 7.5 psi, you might be lifting the needle off the seat, i keep mine at anout 6.5-7 with the blower.

 

[10secgoal]

130 aren't really too big. But the bigger the needle and seat, generally the lower the pressure you can run. It has a bigger suface area that the fuel is pushing down on the needle.

 

[69gmachine]

Thanks for the replies! After getting it all back together, now the solenoid just clicks . Maybe it's just a loose connection, but a wicked cold front blew in last night and I lost the motivation to get out there and lay on that cold concrete floor to find out.

According to my Holley Carburetor and Manifolds book, circa 1976, the required fuel flow for a 400 cu in engine, with a fuel air ratio of .08 (or 12.5 for the air/fuel ratio) and 100% VE (not sure where mine is but certainly less than 100%) at 6000 RPM (my redline) is 250 lbs/hr. A 120 window needle & seat at 6psi delivers 305 lbs/hr. They didn't even make a 130 back then so it's not on the chart. But I can only imagine the 130 window at 7.5psi must be flowing something near 400 lbs/hr. They also didn't make the 97 in a window style back then, but a 97 w/holes at 6 psi delivered 225 lbs/hr. The windows typically flow about 7% more than the holes, so that would put me at 240 lbs/hr. With a realistic VE of 90%, it should be just about right.