[Mark IV]

Originally Posted by 1795

I do not know if anyone took notice, but in an earlier post when I was discussing getting the fuel system installed I mentioned that there were no leaks at 3 psi. Well, the system had no leaks, but 3 psi while allowing for the engine to run at low rpm, was not going to cut it on the race track.

So I tried taking 90 degree fittings out of the circuit to possibly reduce restriction and that did not help. Tried replacing my Carter fuel pump with a Holley that had a 140 gph and 12 psi as compared to the 100 gph and 7 psi rating of the Carter. That did not seem to do much initially, then all of a sudden the pressure gauge started to rise and then jumped around at around 10-14 psi and then the pump quit. The Holley came with a 7.5 amp in-line fuse to be installed, which I did not install because the switch that I was using for the fuel pump was already on a fuse. When the pump quit I figured that I had blown the fuse and then went to the wiring diagram to find the fuse so that I could replace it. I found the fuse and it was not blown, because it was a 25 amp fuse! Lesson learned, always cheek the fuse box to verify the amperage of a fuse that you are going to be using.

I called Dennis Olthoff for some suggestions and he said that the Carter should work fine and it might be a bad pump, but check the pre-filter first to check to see if it was blocked and try to bypass the filter to see if it change anything. So I re-installed the Carter and replaced the 25 amp fuse with a 10 amp fuse that the Carter called for. The only way that I could bypass the fuel filter was to remove the element. I also removed al lines from the fuel cell to the pump and made sure that there were no blockages. Ran the pump and was getting only about .5 psi on the gauge, even after I was certain that there was fuel in the line. This was not making sense, so I unhooked the fuel line from just in front of the fuel log and placed the end in a mason jar. Turned the pump on and after a couple of bursts of fuel and air there was a substantial fuel flow; filled that quart mason jar in about 2 seconds. Reconnected the line and the pressure gauge was reading 3 psi again.

Given the fuel flow it did not make sense. So, as I sat there and pondered the situation I looked at my MGB race car sitting next to the Cobra and decided to switch pressure gauges. Guess what happened? With the engine off I immediately was getting 5 psi and with the engine running and drawing fuel it went up to 6.5 psi! With moderate acceleration it stayed at 6-6.5 psi prior to the fuel log in an 8 AN line. Problem solved.

A rather expensive lesson given the cost of the Holley fuel pump, but a lesson learned.

3 weeks until the big race.

Jim

A hard lesson many of us have been taught the hard way, "New in the box" does not always equate to "Good"!!!