ive got twin 350 mags 300 hp ive been running all summer.today went out for a ride and the port motor under a load started poping i couldnt tell if it was comming from the exhaust or carb.stopped the boat checked the oil no water.pulled the plugs all dry.started the motor ran great untill i put it under a load.back to idle no problem it's not rap what do you think.im running silent choice.oil preasure fine water temp fine.???????????????

I have had a similar problem in the past. Although mine was popping back through the carb. Try checking to see if the exhaust valves are opening, if you have a broken exhaust rocker arm the cyl. can"t exhaust itself so when the intake opens the combustion pressure "pops" back through the carb. could be a worn cam lobe "exhaust" somthing along that line?? maybe?? I also had a head gasket blow between two cyls. that made a slight pop noise. Hope this helps.. Good luck

I'd guess it's a broken valve spring, if you wiped out a cam lobe it would run a little rougher even without a load on it. You might want to pull the valve covers and take a look. Will it start popping if you increase rpm's in neutral?

no in neutral i can rev to 5500 no problem sounds great.i was just thinking could it be the ignition module?again no water and compression is great if it was a bad spring it should have shown on the comp test.

Have we overlooked somthing simple? how long have the spark plugs been in, I have to change mine every season or my motor will pop under load. did you idle for an extended period? (such as down a canel or a river trip?) it could be a simple fix. keep us posted. good luck.

check cap and rotor

new plugs today cap and rotor are fine wires new this season.installed new dist pick up. took off valve covers no broken springs.ran it at idle to 3800 rpm popping started a littlle.brought engine back to 800 rpm fine. could it be a bad coil? it has to be somthing easy i hope.

yesterday i stated it did not pop in neutral it did today 3800 rpm.the boat wasn't at idle for a long ride up the river. but after the popping ran at 2500 5 miles home no problem.

Just had same problem on buddy's boat, had put new wires, plugs, cap... etc... found popping on once and a while at a little about 3000 rpm... problem was finally figured out to be new set of plug wires.... try using your old plug wires and replace your new ones one at a time, we did this and the popping went away... one of the new plug wires was causing the problem... again, our popping was very intermittant, but always at around the same rpm....

Good luck!

went back to te old wires same thing.any more ideas i'll try anything except pay 90.00 an hour