a little over a year ago i found a new in box edelbrock quadrajet. i changed jets and rods and got it running very good . a couple weeks ago it seemed a little flat so i had a new accelerator pump from cliffs left overhand decided to put it in. when i got it apart the edelbrock part looked o.k . but i changed it anyway but not believing that was the problem , well it was. the skirt was not distorted but was scuffed really badly and casual observation may not be enough . if you have an issue change it anyway. maybe Lars and Cliff will chime in.

 

If enough barnacles and fishheads got past the fuel filter, they may have scuffed up the pump bore. Polish it with crocus cloth, and replace the fuel filter.

 

it wasn't caused by dirty fuel. it was caused by alcohol attacking the material.

 

That's impossible. E10 causes no issues.

 

I had two accelerator pumps go bad due to not being compatiable with the gasoline.
I had taken the carburetor to a professional, (or so I thought) to have it rebuilt. it was after that, that the accelerator pump went bad. I took it back and he blamed it on dirty fuel. So he replaces the pump and a couple of weeks later, the same thing.
This time I took it to another guy and he told me there has to be a special accelerator in the carb to be compatiable with the gas in this area. So he replaces the pump with one of these special ones and I haven't had a problem with it since. That was well over a year ago.

 

That's correct, and both Cliff and I see it all the time. I've seen 2 common failure modes on the pumps:

The most common is that the pump rubber swells up, seizing the pump in the bore. This often results in the pump cup getting sheared off the pump shaft, but can also result in the pump simply locking up in the bore. Due to the spring loaded action, the pump shaft will still appear to be functional from external appearances (it still moves up and down), but there will be no pump shot at all.

The second failure mode is a little more subtle. The pump rubber can get hard and actually shrivel up a little and appear to erode - just as you observed. This will not lock the pump up in the bore, but will produce a "weak" pump shot. It's actually a little difficult to spot, because you will still see a pump discharge when looking down the venturi of the carb. But the discharge is much weaker (lower volume) than it should be. I've caught these problems regularly on my test engine: The engine will not have good throttle response, even though the accel pump appears to be working. Swap the pump out with a known-good pump, and it suddenly comes alive as it should.

Good job finding the problem and getting a good part installed!

Lars