Occasional stumbling

[JohnKcj5]

Occasionally I can be revving through the higher RPM range(~3000) winding out first and second gear and the engine starts to cut in and out. If I let off the gas it's stops cutting out but doesn't have any power. As soon as I throttle it, it repeats the problem. If I just baby it for about a 1/2 mile the problem goes away. I can't purposely replicate the problem, which makes it difficult to diagnose. It's almost like the carb bowls have gone dry and have to refill. But like I said, I tried revving the out of it and can't get it to cut out. This last tank of gas was from a relatively new Shell station. 87 octane. If it was fuel, wouldn't it buck all the time?

 

[Torxhead]

I have had issues from getting bad gas from the pump. In the form of gas with water in it. There are additives that can help, you can look online for options there. You might want to make sure you are getting enough gas by doing a pressure test to make sure the pump is operating correctly or have any obstructions in there like even a bad fuel filter. A low carb float bowl level is another possibility. These old Jeeps can have rotted fuel lines that have not been replaced also, creating air in the lines. This could be an ignition issue also, but it does sound like you are low on fuel. You just have to eliminate all these possibilities.

 

[Lumpy Grits]

Run prem gas, and try without the gas cap in place.
OLG

 

[Stonefly]

I was having a similar issue and it turned out the accelerator pump gasket on was bad. The blown gasket allowed fuel to leak through the vent hole on the cover plate and collect on the intake. It was an easy and cheap fix (20 min / $12 gasket) and it potentially prevented a catastrophic fire.

 

[JeffP]

I agree completely with the first two responses... it’s starved for fuel or “good fuel”. Check the filter(s) first.
I normally run glass filters so I can see what’s going on. I also carry a few extra filter cartridges if I get into trouble out in the desert.
However it could be ignition related too. Check the primary voltage and make sure the wires aren’t corroded or frayed. Frayed wire can reduce current, while the voltage is correct it doesn’t have enough Wheaties for higher rpm.

 

[JohnKcj5]

Thanks for the suggestions, guys. Keep'em coming. I believe the accelerator pump gasket is specific to Holley, right? I'm running an Edelbrock. I'm gonna run this tank out and fill up with non-ethanol. Add a bottle of Heet and try a new filter.

 

[Lumpy Grits]

Does this happen after the engine is good and hot? Vapor lock maybe.
When was the last time you replaced the fuel filter?
When was the last time you confirmed ign timing and replaced dizzy cap, rotor and SP wires and plugs?
Have you checked for vacuum leaks?
LG

 

[JeffP]

Thanks for the suggestions, guys. Keep'em coming. I believe the accelerator pump gasket is specific to Holley, right? I'm running an Edelbrock. I'm gonna run this tank out and fill up with non-ethanol. Add a bottle of Heet and try a new filter.

The “Edelbrock” series carburetors are copies of the old Weber carburetors. As such you should find an accelerator pump that is mounted vertically on the top of driver’s side front corner.
However, that would only be a problem the first few seconds under acceleration. Example starting from a dead stop, floor the pedal and it will almost quit, 2-3 seconds later it will respond. If it’s not doing that, it isn’t your problem.
Again, check fuel delivery to carburetor and primary ignition first.

 

[JeffP]

Occasionally I can be revving through the higher RPM range(~3000) winding out first and second gear and the engine starts to cut in and out. If I let off the gas it's stops cutting out but doesn't have any power. As soon as I throttle it, it repeats the problem. If I just baby it for about a 1/2 mile the problem goes away. I can't purposely replicate the problem, which makes it difficult to diagnose. It's almost like the carb bowls have gone dry and have to refill. But like I said, I tried revving the out of it and can't get it to cut out. This last tank of gas was from a relatively new Shell station. 87 octane. If it was fuel, wouldn't it buck all the time?

I just read this again and I’m 99% certain you have restricted fuel delivery. Such as a clogged filter!
The bowls will fill at lower rpm but as demand increases, the flow can’t keep up with consumption.
Check the filter(s)! If the filter appears clean, remove the line and test the volume of fuel coming from the pump. There is also a “sock” type filter in the tank.