I have a 1965 Chevrolet with the original 396 engine. When I purchased the car, I noticed the fuel pump was wet with fuel at the weep holes. I replaced the pump with a new one. This pump also leaked at the weep holes. I thought dirt may have been in the fuel tank and the ckeck valves were stuck causing the leak. I installed a glass inline fuel filter before the fuel pump and installed another new pump. There is no dirt in the filter. This pump also is leaking from the weep holes. The pump only leaks when I give it full throttle and bring the car up well over 65 mph. I would like to retain the stock type of fuel pump. I’m wondering if the pump push rod is a replacement at some time and too long. Any suggestions?
What brand of fuel pumps are you using?
If a mechanical pump leaks fuel at the weep hole it is defective or damaged and nothing done external to the pump will correct the problem. Does the pump have a 2nd smaller nipple for a smaller rubber fuel line like this
and the smaller nipple is capped? Those pumps require an external pressure relief valve in a line that returns to the tank.
Pump pressure is determined by the diaphram spring and not the push rod.
Did you use a NOS original pump? If so ethanol may be quickly damaging the diaphram.
Grasping a bit here, but if it’s not related to the pushrod or Ethanol any chance of the crankcase pressuring up excessively and rupturing the diaphragm?
Is the engine oil being contaminated with gasoline?
That early model had a large open vent from the valve cover to the air filter housing @ok4450. And while excess blowby could cause crankcase oil to weep from the fuel pump the OP specified fuel was leaking.
Excellent that you thought of the fuel entering the crankcase. It is very likely that the engine oil is contaminated at this point. Hopefully the OP will change the oil before restarting the engine.