Author Topic: Accelerator Pump Seal Testing  (Read 453 times)

Offline Cliff Ruggles

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Accelerator Pump Seal Testing
« on: September 15, 2021, 03:44:22 AM »
This is a MUST READ. 

I keep getting calls to the shop for "free technical advice" and one of the most common topics is difficult starting after the vehicle has sat for a day or so. 

EVERYONE is thinking that the bottom plugs are leaking down so wanting to seal things up there.  Most have just "rebuilt" there carburetors with cheap kits so NOT wanting to buy anything thinking they are good to go there.

So I ask each person who calls here what would happen if they sent a carb here and got it back, and installed it dry without putting fuel in the bowl?

It the carb re-filled  quickly the engine should roar to life with just a few pumps on the throttle, correct?

99 percent of the poor starting issues are a failed or failing accl pump, not a bottom plug leaking or empty carburetor issue.

This happens because the kits folks are buying have "blue" and "black" seals on the pumps that are failing quickly when they come in contact with this new fuel.

So yesterday I pulled two pumps out of NAPA kits, typically regarded as top quality components in this industry (even though they actually come from the same source most other kits do).

Anyhow, I took some fresh BP 93 octane fuel advertised to have 10 percent ethanol in it.  All three pump seals were removed from the pumps and put in the fuel at the same time.

At 15 minutes the "black" seal had already swelled up some.  The light blue seal, although still pretty much the same size was staring to get really "soft" to the touch or felt like it was made of silicone. 

After 3 hours the black seal had grown in height at over .110" in diameter!  It will no long fit in a Quadrajet accl pump bore without considerable effect to get it in there.

The light blue seal had grown just over .020" and starting to get a little tight in the pump bore.

My seal is exactly the same size/shape that it started out at.

I will continue this test and upgrade the thread over the next week or so.......Cliff

The first pic below are three seals after 15 minutes soak time.  The one I sell is on the left, the center is the NAPA blue seal, the right is the NAPA black seal.  You can see that after 15 minutes the black seal has already grown some.

The bottom pic is the black seal after 3 hours soak time.

Offline Cliff Ruggles

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Re: Accelerator Pump Seal Testing
« Reply #1 on: September 17, 2021, 04:19:19 AM »
Update on the seal testing.  The black seal stopped swelling up but it had already got so big it will not fit in the pump bore or even stay on the pump!

The light blue seals NAPA/Walker swelled up about .030" in diameter and .020" in height.  It also broke when I tried to stretch it out.  I could also break pieces off of it, the material is no longer pliable or serviceable.

The seal I use hasn't grown any in diameter or height, and you can't rip or tear it.  Even stretching it out quite a bit it returns to it's original size.

Since I broke the light blue seal I started the soak test over and will leave all of them in fuel for a couple of weeks to see what happens.

It's a little difficult to see how much it has grown but the seal that was soaking in fuel is on the right in the first pic.  The second pic is the seal after failing the "stretch" test.  It broke very easily and I was able to tear it with my fingers. 

If anyone wants to do any testing of their own PM me or call the shop.  I'd LOVE to get a few second opinions on this and have them put their results up here......Cliff