Popping and revving?

[tphoyt]

I’m very curious. Can you explain inconsistent fuel pressure?

 

[Mystic Mariner]

When the engine first started (cold), I had had good fuel pressure (put a T-fitting and gauge on the output line). Once the engine got hot the pressure would fluctuate intermittently. Pulled the pump and rebuilt it. Noticed the gasket between the pump and block (seals the pulse port from block to pump) was pretty deteriorated. Evidently from thermal expansion the gasket would leak as the engine came up to temp and would start leaking. The pulse wasn’t strong enough to actuate the diaphragm in the pump. Before I rebuilt the whole pump, I ended up just putting a new gasket over the pulse port and didn’t have a problem while running. I decided to rebuild the rest of the pump as the diaphragm was pretty deformed.

 

[F_R]

The motor had a classic symptom of not getting enough gas to maintain proper fuel to air ratio, Causes can be varied, from running the tank dry to unplugging the fuel hose to sucking air from a leak in the hose, to yes carb sync, etc, etc. And of course, the fuel pump.