I believe this is a 4160 vac Secondary carb. I'n new to Holley carbs. Last summer the imperial would not run or idle well, and it turned out to be the rear float valve had crud in it, and the high fuel level was leaking into the engine. Got an Edelbrock carb kit locally, cleaned the fuel bowls and all is well.. ended up only using the float bowl gaskets at that time, the rest of the carb kit went on the shelf. Car just quit while idling, and a puddle under the secondary throttle shaft lead me to pull the carb and have a look-see. Sure enough black grit like stuff in the rear float bowl. I have had a fuel filter just in front of the carb inlet the whole time. . . It is a metal filter, so I do not know if it is catching a lot of junk or not. A couple of questions: Where can I get some "great" float bowl gaskets? The Original ones were blue, and stuck like glue to both half's of the float bowl surfaces.. The black ones just ripped on the primary side as well.. is there a better solution regarding gaskets? does soaking them in WD40 or something of the like get them to release better? Does the fact that it is the rear float bowl that is getting the sediment, suggest a problem within the carb? I did not think to see if the black grit was actually sand, or rubber, or what it was.. And I just had the question pop up: the rear float bowl should not be getting much fuel, as the car is not even being driven on the road, only moved out of the shop and around the yard, to get it out of the way of what ever project is in full swing. So it would seem that the rear float bowl should have stale fuel in it by now.. any thought or suggestions welcome.