Wierd fuel pressure and hard start issue

[my5thmopar]

This is in my 70 D200 with a 383. After setting for 4-5 days I have to crank and crank. I've checked the carb and there isn't any fuel when the throttle is pumped, hence the crank and crank. I rebuilt the carb and replaced the fuel pump. I checked the fuel pressure today and it was 7-8 psi at idle. Here it the weird part...After shut down the pressure climbed to 12 psi. I've never seen this before and I suspect it is overriding the needle and seat letting the fuel overflow the carb. Any suggestions or questions to figure this out. Thanks Craig

 

[GeorgeH]

Heat soak/fuel Percolation after shutdown? There are thick heat isolator gaskets and or heat shields available. What carb?

 

[my5thmopar]

I don't think it is heat and it has the 3/8 thick carb gasket. This engine has a 4 core radiator and runs pretty cool. It has the factory carter 2bbl and I use non-ethanol gas. I removed the gas cap and it didn't change the after shut down pressure climbing to 12 psi.

 

[AJ/FormS]

What type of pump;mechanical or electric?With or without a regulator?, with or without a fuel return?

I'll go with what George said.
The pressure rise is NOT from boiling in the carb tho,lol. But rather the fuel is trying to boil in the line between the float valves and the pump. You need to insulate the steel supply line, and minimize the amount of rubber in that area. Get rid of any plastic fuel filter you might have. The purpose of these changes is to reduce the heat getting into the fuel line.
Once the fuel is in the bowls, it cannot affect the fuel pressure gauge, as described. It may boil away or evaporate, or leak out, but it cannot cause the pressure to rise in the line.
But IMO you have multiple problems.
>If I had to guess, it would be that some part of the fuel line is in direct contact with something hot, or the fuel is boiling in the mechanical pump that is bolted to the engine.That is the first problem.
>The second is the lack of fuel in the carb 5 days later.At this time of year, the filling stations are probably still stocking winter gas that has a lower point of vaporization. My guess is you got a load of that in your tank, and it is simply evaporating.
Here is a test for that
Put some of that gas in a clear lidless jar, and mark the liquid level with a Sharpie.Set it under the hood somewhere. Come back every 24 hours and note the loss of fluid.
>And finally, if the choke is working correctly, it should still start, allbeit with a long crank time.
>PS I have seen many of those BBSs do this for no apparent reason, and many guys have installed a draw-thru electric pump and just prime the system before every start.

 

[my5thmopar]

First thanks for the help.Craig
Pulled out the needle/seat looking for trash and there was none.
Mechanical pump from parts store, no regulator and no fuel return. These trucks have vented cap and one hose from tank to pump.
Will check line to see if touching something hot and insulate.
Metal fuel filter.
Just filled up from empty will fresh non-ethanol gas.
Choke is working correctly, first thing I checked.

 

[AJ/FormS]

Also, 7/8 psi at idle is too much for most float valves. It tends to over-fill the bowls, and the engine runs rich.
The fact that you are seeing 12 on the gauge says one of two things; 1) the float valves are taking it, and not flooding, so possibly the wrong float valve is in there, or 2) your gauge is somewhat optimistic.
To prove a rich running condition, due to a too-high fuel level in the bowl, at idle, simply pinch the rubber part closed up tight, and let the engine continue to idle.
One of three things is going to happen: the engine idle speed is going to:
1) slow down until it stalls, or
2) stay the same for a bit, and then continue as in 1)
3) the idle is going to rise and rise,then level out and continue as in 2) above.

1) is lean, 2) is just right, and 3) is rich

You cannot arbitrarily mess with the fuel level. The other circuits are calibrated to the factory fuel level. But if the hi fuel pressure is causing a hi fuel level, something needs to be done about that.