flat spot in acceleration.
 

1963 suburban, all original 305E with a really nasty dead / flat spot just off idle. Its difficult to describe via text the stumble / dead / flat spot is sharp and sounds like it is SUDDENLY starving for fuel or fouling a couple plugs or??? This truck sat for 20+ years. We cleaned the tank, replaced rubber fuel line, rebuilt the carb, flushed the cooling system, primed the oil pump, and changed the oil. The original fuel pump was already replaced with an electric one long before we owned it so I also just replaced the old pump with a fresh, new electric one.

It ran like a champ for 1000 +/- miles but has developed a dead spot that occurs just after the accelerator is pressed slowly. If the accelerator is pressed quickly to the floor, the dead spot is non-existent or so slight that its hardly noticeable.

Thinking the issue may be timing related (and wanting to convert to HEI anyway) I ordered a new HEI unit custom built for this engine by HEIDIZZY in Woodruff SC. Installed all new plugs, wires at the same time.

Purrs like a kitten at idle but still has the flat spot just off of idle... What now, rebuild the carburetor again? The issue did not change at all withe the new ignition system.

Re: flat spot in acceleration.
 

There is actually a name for this behavior. It is called "tip-in sag" and is definitely a carburetion problem. A rebuild is likely the best way to attack it, taking special care to make sure that all the small passages are clear.

Ray

Re: flat spot in acceleration.
 

A side question here pls. You mentioned on the start up procedure, changing the oil, and priming the oil pump. I'm cleaing up the bottom of my engine, getting out the old sludge, fixing the bent up oil pan, removing, dissassembling, and cleaning the oil pump and screen. When I put the assembled pump back up in there, how do I "prime the oil pump"? Engine has not run in 23 years. Tks.

Re: flat spot in acceleration.
 

I know on small block Chevys, you can make something that fits down in the distributor hole tho turn the oil pump with a drill. All I did was unplugged the coil and electric fuel pump and turned the motor over a few times until I had oil pressure.

Before that, I squirted some ATF in each cylinder and slowly turned the engine over by hand to make sure I didn't have any sticky rings.

Probably better ways to get it done but I had to work with what I had on hand.

Re: flat spot in acceleration.
 

Is your accelerator pump working correctly???

Re: flat spot in acceleration.
 

Not sure if it's working or not. I will have to check it out this weekend.