74ZZ430

I have a 74 with a copy of a ZZ430 motor, except I'm using a Qjet with a Edelbrock 110gph mechanical pump. The car has always ran good and my wide band oxygen sensor would read about 13.2 at WOT. However this year even though the car still seems to run fine, it is running lean at around 14.6 at WOT, it starts going lean as soon as the secondarys start opening up. I have change everthing I can think of. The fuel pump, filter,( I'm not using the in carb filter), all hoses, in tank strainer even tried a different carb, and rebuilt both carbs, all made no difference. I was using a fuel bypass set at 6 lbs. I removed it today and have about 10 lbs of pressure at 2000 rpms. The fuel pressure did do something strange today. I had been running the car hard and the fuel pressure hadn't changed much, and then under moderate acceleration the pressure dropped to about 3 lbs and then came back up after I let up. Any suggestions would be appreciated.

SH-60B

Maybe the o2 sensor is not reading right.

74ZZ430

I though about that, I did recalibrate it. The strange thing is as long as you dont bring in the secondarys the air fuel stays fine. It sometimes. goes a little rich, 11.5 when just accelerating hard on just the primarys.

cardo0

Well its hard to see what your measuring fuel press with from here in California. If its one of those tiny liguid filled inline gauges toss it. If its an air filled gauge or an electronic fuel gauge then u really are loosing fuel press on acceleration. If so that would mean either the fuel bowls are emptied too fast (unlikely) or the fuel is getting dumped some where. Or possibly too much restriction in the fuel line. The fuel line is losing suction when u accelerate and could be a pinch in the line or line is just too small for that ZZ430 with a bypass.
Yes, i blame the bypass dumping too much fuel and press when u accelerate - most likely. Just my 2 pennys recheck your bypass setup.

cardo0

74ZZ430

The gauge I'm using is a large approx 4 inch diameter air filled unit I purchased from Napa. I also thought the bypass might be the problem so I removed it from the system, my pressure went to 10 lbs, but had no effect on my problem.