I recently bought a 1977 24' excalibur. I has been running fine and one day out on the lake it started making a noise at about 3500 rpm. I let off and it went away. I planed out again and the noise came back. but when I went back to idle it kept making the noise. At home the next day on the hose the noise sounded as if it was coming from the carb. Very regular noise. then I throttled it to about 3000 rpm and back to idle and then the popping was sperratic and not very loud. Could it be bad gas.?? a lean condition.? Changed the fuel filter, but still doing it. The engine is a built 454 w/ aluminum heads, steel crank. Any ideas?? Thanks Eric

Possibly a bad intake valve, perform a compression test on the engine. If any cylinder is down more than 10% do a leakdown on that cylinder-you will likely hear air from the intake.

have to agree with ted ( well dont have to but but as usual hes right ) more then likely it is a burnt, stuck intake valve or a bad spring

you could also check for loose wiring, on coil and what not. Look at you distrib rotor...make sure distributer is nice and dry inside....stuff like that.

Thanks guys for the Ideas. The guy I bought the boat from suggested I change the fuel filter. He said to make sure and put in good quality gas. I think I put in bad gas. Changed the filter and the noise went away. Also added some 110 octane race gas to boost up gas that was in it. seems to be running fine now!! Thanks, Eric