Using stock carb modified by the engine builder my fuel pressure is all over the map. From low of 1 to high of 5lbs. At beginning of the season ran at 3lbs from startup to shutdown. Have changed pump, filter, regulator with no change. Engine sometimes dies in corners and at end of straight. Is it a carb issue?

 

A lot of pressure regulators will have burrs inside that will cause fluctuations in pressure. You have to disassemble them and clean out the bore...

 

it sounds like it was working fine before, so probably not burrs. I'd check the fuel pickup, but i suppose it could be the carb as well...

 

If its fluctuating at a gauge before the carb, I would be checking things between the gauge and the tank. If the hardlines were left open for a while during swap of pump, or a line was left loose, there could be some **** in there. I'd recommend filling it with carb cleaner and a squirt with some high pressure air, anything in there will no longer be.

If you've ruled out everything but the tank, it could be the sock on the pickup is nearly completely stopped up. That's a relatively easy fix, unless the reason its stopped up is floating around in the bottom of the tank... but its not terribly hard to clean them out unless its rust.

 

Don't see how it can be a carb problem if the fuel pressure is all over the board. At 5lbs the nikki will easily flood as the floats can't hold it back. At 1lb you can be running the float bowl empty.

Why first guess would have been a bad regulator. Personally I tried several low buck NAPA style regulators in combination with my 7lb carter and the regulator would start at 3.25 and slowly creap past 4 and 5lbs until it flooded.

If at times you get down to 1lb of fuel pressure I would consider two other problems. One is that the pump has enough pressure but not enough volume. At low RPM you may be able to get 5 lbs but at high volume it drops to 1lb which may not give enough total volume. Stock type low volume pumps did this. Especially if line or filter is partially plugged. Can you read fuel pressure in the car while racing? Is pressure low at end of long straight? If so this could be it.

The other thing I would look at is the ground on the fuel pump. I had a ground that slowly corroded and when I hit the brakes the fuel pump would cut out and if I stayed on the brake to long the floats emptied and the motor died. With the motor running I couldn't hear when the pump wasn't running.

This may not have anything to do with it but as long as you are doing maintenance blow out the hard fuel lines, replace the rubber fuel lines and check the pick up in the tank. Sounds like you checked everything else.