truckerlary

I've been dealing with this problem for a while and thought maybe some help from the forum might help. With the engine running at idle the fuel pressure runs about 6 1/2 to 7 lbs but when I fast idle to about 3000 rpms for a little while the pressure drops to around 3 lbs. My problem is when going thru the gears when I go into 3rd and am getting on it the engine seems to shut down with what seems due to a lack of fuel. I let off the gas and it keeps on running. I've changed carbs but still does the same. Manual pump was new about a year ago when I built the engine. Probably has 300 miles at most. Has had all the rubber fuel lines replaced. Thought might be a restriction so took an air hose and blew back thru the lines but no help. Any ideas. Could the fuel pump be bad? I'm thinking I got it at NAPA. Car is a 75. Thanks Larry

hraponte

Larry,

I would check the fuel pump, again. It may sound crazy, but I had the same problem with a helicopter. Replaced the fuel pump three times before I got a good one. Same thing happened with a generator (replaced four times before getting a good one). The pump might be pushing enough fuel to maintain pressure at low rpm, but not for higher.

Hope this helps.

71VetteLover

It's possible the sock filter in the tank is plugged up but it's also very possible the new fuel pump is no good. Fuel pumps used to be very reliable but I have a hunch they're all getting check valves made in China because I have heard of MANY new fuel pumps fail; regardless of their brand. That's why I went to an electric pump 5 years ago.

To test your fuel pump disconnect the steel fuel line from the carburetor and slip a 2 foot length of 3/8" hose onto the end of the line. Stick the other end of the hose into a large coffee can or something similar. Crank your engine and it SHOULD deliver 1-1/2 pints (24 ounces) in 30 seconds.

truckerlary

The check valve is non existing because as soon as I shut off the engine the pressure gauge drops to zero.

ariba

I did bought a new fuel pump for my GM SB 350/290. I dont remember the brant but it was from advance auto it gave me a headache. It was sending a lot of fuel, I resolved it with a fuel regulator.

https://www.summitracing.com/parts/sum-g3032b


It sounds like the fuel pump but there is a lot of people hear are more expert than me they can correct me if am wrong!..

Grumpy 427

Rule of thumb. Minimum of 5 psi through the top end floored. If your at 3, under acceleration you either have too small of pump for your application or a bad pump. I have an Edelbrock 110 mechanical with 3/8 NPT fittings in and out, on my 355 sbc 350 hp have had no issues. Your issue is not enough VOLUME., Pressure is not a substitute for volume. I would put a minimum of 110GPH pump on any car.

71VetteLover

A mechanical fuel pump has two one-way check valves and if either of them won't hold pressure the pump is no good. The "American Made" fuel pumps may be assembled in America but that doesn't mean ALL of the parts are made in America. I bought a Pierce fuel pump for my 454" about 5 years ago and immediately had trouble with it. I cut it apart and found neither of its two check valves were holding pressure so I converted to a Carter 100 gph electric fuel pump. Since then I have read many posts about failing fuel pumps of EVERY brand which makes me suspect they're all using Chinese check valves.

In 2010 I discovered all of the American Made TH700R4 filters were using Chinese o-rings that shrunk really bad when exposed to hot oil. The o-rings shrunk so bad they would literally fall off the neck of the filter as their I.D. expanded about .025" while their O.D. shrunk about .025". So the term "American Made" really means "Assembled In America".

truckerlary

Put a new mechanical pump on and now runs super. Question I have now is that the fuel pressure runs a steady 7 1/2 to 8 lbs. Does this pressure need a regulator installed to bring it down a couple pounds. Thinking its a tad high on the needle and seat. Pump I installed was a carter that specs said flows around 110. Thanks Larry

Grumpy 427

If Its a Holley carb, No they run at that pressure. Most preset pumps are bolt on and go no regulator required.

truckerlary

It is a quadrajet

Grumpy 427

Ok well my Eddy 110 pump sits at around 6.5 psi i had a Qj on it for a bit then an eddy 1406 not a holley . The needle and seats are pretty tough

Grumpy 427

Look at stock eliminator those guys run Qj with electric pumps they have to be set to at least 7 psi to maintain 5 through the top end

71VetteLover

You need to sweat solder a 1/8" NPT brass "T" into your fuel line and then run a hose and gauge up to your windshield so you can see how much pressure it's producing at a full throttle and high rpm.

To install the "T" drill the 1/8" NPT brass "T" with a .375" bit lengthwise, cut your fuel line with a mini tubing cutter, slip the "T" into place with the cut ends of the fuel line in the center of the "T", then sweat solder it into place.