The Stovebolt Site Forums The Shop Area Engine Shop 54 GMC 450 carburetor flooding

I hope I can get some advice on this problem. 302 engine , Holley carb. Has a tag that says List 660.
I try to run this old fire truck a bit each summer. It has always run great.
The six volt battery holds a charge from year to year.
This week I started it, and it began to flood badly.
I thought the float valve might be sticking open, but had it apart and its clean and normal, isn’t running over.
Looking down the intake, there is a stream of gas pouring down the center.
I have been putting in the usual ethanol gas, and haven’t drained or otherwise winterized the fuel system.
Maybe a mistake. I would appreciate any input on this, what to try, or check.
Charley[img]https://www.stovebolt.com/ubbthread...FF32104-0293-44B5-B67D-91F794BFE360.jpeg[/img]

As a far as Ethanol gas, I would drain all of it now.
You need a commercial water separator and contaminant filter made for Ethanol gasoline. They have the large filter cartridge.
Run a separate line to a new/rebuilt fuel pump.
Add a new fine micron filter and a new line to the carburetor.

You can try to PM Tim. Member name "tclederman". He has the 261 with the AA-1 carburetor.
He may be of more help than myself.

I'm not familiar with any Holley carburetor but looking at a diagram for the AA-1, I see:

Item 54, "Economizer Valve Assembly".
Item 53, "Pump discharge valve".
Item 60, "Pump Check Valve".
My guess is that any of these could cause leakage.

Charley,

Some on-line checking indicates your Holley "List 660" carb appears to be original equipment for your "old fire truck". By definition, this is listed as a Holley Model AA-1 (see screenshot attached taken from the below web site listing - all credit to "The Carburetor Shop" for posting this information for all to use).

https://www.thecarburetorshop.com/TruckkitsG.htm#TkitGMC

I myself don't have any experience with this model carb, but others will hopefully chime in with some help on what might be causing your predicament.

Will note that many have suffered the results of ethanol in today's fuels and its bad effects for older equipment not designed for it's use.

Dan

Any time a carb floods like that, gas is getting by the needle & seat. It could be dirt between the needle & seat or the needle might be stuck open. I might be the float is full of gas or stuck to the bottom of the bowel.

George

Thank you fellas for the responses. And I concur on the carburetor shop, very generous and helpful info.
One thing I tried was to close both the jet screws at the bottom of the carburetor experimentally, to see if it made any difference at all. It didn’t. I noted the number of turns and put them back the same.
So, I did check and clean out the float bowl, the float valve, needle and seat looked clean and normal, and the level was down where it should be. Only some fine dirt in the bottom. The inline filter is functioning.
The items buoymaker mentioned for the AA-1 to check, sounds possible.
So, I’ll let you know if I have any luck!

Those two bottom screws you adjusted are idle adj., normally ride about 1.5 turns open.

Ed

Check the condition of the power/economizer valve (buoymaker comment 54).

Jon

OK. So, I’m obviously not going to avoid taking the Holley apart🙂
I am on the right track now, and I’ll report the results.
Again, this engine has run great right up to this occasion, so I feel confident
in getting the carburetor to work.
Thanks to you all.
A great bunch.
C