loud pop when taking off
 

i have a 25' OL with a 502mpi and bravo 1 out drive. this past weekend i was planing out and the boat made a a few popping sounds when under full throttle talking off. i had 6 people in the boat witch is a lot of wait and 50+ gls of gas in it also. not sure it it was from the trans or motor. it ran fine and didnt jolt or loses power when it made the noise. the temp was great and oil pressure was good to.

i talked to david wade marine. (davidwademarine.com old throttle man for the popeyes race boat) they said it sounded like a backfire into the intake from old gas plugs wires and rotor and cap. i am new to this game and have no clue were to start. i just know it shouldnt pop like that. ill answer and questions for some help. i am going to get all the gas out and put new plugs in and see what happens. other than that i am lost.

Is this a new to you boat ?

Thats what i would do !!! And check timing !!

From what you described, it does sound like a lean condition backfire.( popping through carb). How old is the fuel?? How long has it been since the boat has had a full service?? Like David said, fresh fuel, and a good tune up would be a good place to start.





Darrell.

Casey,

I had a 97 Donzi 27 ZX with a 500HP Carb motor and had the exact same problem. My wrench kept changing the power valve in the carb. It would work for a little while and then the popping would start again. You might need some new valve springs, that's what cured mine.

Good Luck, it took a while and a few power valves to figure that one out.

Mark

no the baots not new, its a 2000. with 420hr on the motor. its been well cared for i know the guy i bought it from. its a efi motor and the gas is been in there since sep. oct. some were in there i was planing to run it out, but work and weather didnt let me. i havent lost any proformance at all eather

If you have marginal plugs, plug wires or rotor/cap, and with the high load on the engine getting on plane, you may experience spark jump and misfire. It's harder to fire that plug under high load and getting on plane is when a problem like that would show up. May run fine just cruising. I agree with David Wade to start there. Good luck!

Just went through the same thing on my fathers Sunsation 288 with a 496. It was a cracked spark plug, backfiring through the spark arrestor screen. Change the plugs and I bet it goes away.

What they all said.

Full tune up and fresh fuel.

were is the bast place to get the cap, rotor, plug wires ( stick with factory or aftermarket if witch ones) and also whats the best plug to use? thinks off all the help!!!!!!!!

I would stick with factory. There is www.mercruiserparts.com I have never purchased through them, but I believe all the parts are factory and they have a nice website. Maybe someone can comment. They are an advertiser here (Bam Marine).

For a new cap, rotor, spark plugs, wires and a 6-pack you are probably looking at $150-$175. Not bad.:drink:

You shouldn't need plug wires. Just inspect them for cracking first.

I use merc caps and rotors. Get the spark plugs at an automotive store. I prefer NGK's. NGK Part # is BR6FS stock #4323. BTW, I have 2000 502mpi's as well.