Irregular fuel pressure

[67cuda360]

What would cause irregular fuel pressure when the engine is hot?

I noticed a lag of power when i floor it, only when the engine is hot (ran 195 degrees when i noticed the lag of power with a 180 thermostat) It was pretty warm here today, probably around 25-27 degrees Celsius outside and i was running her hard, so the temperature doesn't surprise me (my car doesn't have a fan shroud).

I had a fuel problem last year and i replaced the Fuel pump with a new mechanical fuel pump. My fuel pressure gauge reads a mostly steady 4.5 -5 psi but drops down to 3 psi every now and then (idling in my driveway). what could cause this?

Below are some specs of my car:

My barracuda has a warmed over 360 with a edelbrock 650 cfm carb backed by a 727. I have a 1 inch spacer between the intake to insulate the carb from heat. fuel tank looks brand new and so does the fuel sending unit, fuel filter is new and shows clean and clear.

My Timing is set at around 16 initial and i believe 35 total with not exceeding 50-52 with the vacuum advance all in. (don't think it is a timing issue since the car runs great when cold and starts easy even when it is hot)

Any ideas...?

 

[hellion_locdogg]

Sounds like idle air mixture to me.

 

[67cuda360]

Sounds like idle air mixture to me.

But that wouldn't affect fuel pressure would it? I have set the idle air mixture screws (on the front of the carb) right at the point where they don't increase engine RPM anymore (while turning the screws) and where the manifold vacuum is at its highest. My car idles at a steady 650 rpm with 21 inches of vacuum.

 

[omahamoparguy]

more like fuel percolation with todays new fuels. If you can, run a bypass filter with a return to the fuel tank. Another idea is to use some fuel injection hose instead of hard line. it insulates much better. Also, the quality of standard over the counter fuel pumps is not that good. Of course, quality fuel pumps are way expensive. try to keep the heat away from the fuel line to the carb from the pump. Another problem with the cheap pumps is that the built in one way valves sometimes leakdown and cause hard starting.
Its all supply and demand- there is not a big demand for mechanical pumps these days so that effects the quality. Same thing goes for the alchohol in the gasoline- not at all good for a car with a carburetor but works just fine in a fuel injected application with tons of pressure and a big return to the tank to keep the percolation down.

 

[hellion_locdogg]

If it burps or misses and the idle drops, yes fuel pressure will drop momentarily. Also make sure you have a big enough air filter, it will mess with metering if you don't. It also may just be that your mech fuel pump can't keep up with your carb, but that shouldn't be an issue at idle.