Small Block Chevy, Popping Thru Carb.

I'M A NEW MEMBER AND HAVE A QUESTION FOR YOU ENGINE GUYS OUT THERE. I RECENTLY WENT OUT FISHING ON MY COUSINS BOAT WHICH IS POWERED BY TWO CHEVY SMALLBLOCKS. HE TOLD ME ONE ENGINE, AFTER IT GET WARMED UP STARTS TO POP THROUGH THE CARB. WE WENT OUT FISHING AND AFTER ABOUT 35 MINUTES RUNNING AT ABOUT 3000 RPM'S THE RIGHT ENGINE STARTED TO OCCASIONALLY "POP" THROUGH THE CARB. I INITIALLY THOUGHT IT MIGHT BE TIMING BUT THEN I THINK IT WOULD "POP" CONSISTENTLY, NOT ONLY WHEN IT WARMS UP. ANY FEEDBACK WOULD BE APPRECIATED.

Hopefully he doesn't have Holley carbs on it, since with all that backfiring the power valve would be gettin abused quite a bit. I have seen it quite a bit on startup but not when running consistently at a steady load. There might be a leak in the carb (fuel, vacuum of some sort), or for some reason I am thinking that it is possible that the valve is not closing completely and he is getting some combustion to sneak back up the intake...how loud is this popping and does it sound sort of consistent, almost like it is one cylinder? However, that whole open valve thing is sorta rare, so my best guess is that some air/fuel mixture is igniting before it gets into the cylinder. I can only think of a couple of things...I am far too young to be any kind of expert on the subject. Hopefully someone else is more help to you.

Water in the fuel is a big problem with boats...The tanks sweat and create a lot of moisture that gets thru regular fuel filters...A water seperater filter system works best....IF.!!....the element is changed regularly....Water just won't pass thru the passageways of a carb ver well....Keeps the fuel tank (s) full as possible and use a gas dryer of some sort...And of course water/gas mixture doesn't burn so well causing a lean condition and back fire...Just one of the many problems with boats....Damn things..:LOL:

Or he could have a bad lobe on his cam

I had been thinking that maybe a guide was getting sticky once it warmed up...not sure though. And water in the fuel on a boat was a consideration...but only one seems to be doing it, so it could be only one tank if there are two tanks, or a bad fuel line. Could be a bad seat or valve like Streets said. Do some diagnostics on that ol Chebby and see if you have any of these problems.

If the engine run's fine when It's cold and it start's popping when it warm's up, it could be your choke on your carb . If it has a Rochester carb the chance's are good it's a carb problem. It's agood place to start .Good luck .

more than likley its a lobe worn on the cam

Thanks to the members who responded to my question. We took the heads off the motor and brought them to a machine shop. The problem was a valve guide that he said had something like a burr on it. We had the heads rebuilt and the engines run perfect now. Thanks again