knock noise/stalls

[clasavi]

i have a 1998 mercruiser 350 magnum bravo outdrive. i had the seawater pump and impeller replaced today. on the first test drive, the boat ran great however 2 hours later, on my way to a night cruise, the engine made a loud metal popping sound as i approached 15-20 mph and stalled. the boat runs great at low speed between 1000-2000 rpm. Also, when revving it in neutral, it still stalls slightly, but there is no popping or knocking sound. can anyone give me some idea to what it may be. the engine was rebuilt last year...

 

[hartv427]

Re: knock noise/stalls

I could be your running lean you might want to check for a fuel restriction ... fuel filters, anti-siphon valve ...

 

[clasavi]

Re: knock noise/stalls

well, the boat ran fine 20 minutes prior. also, what about the sporadic noise coming from the engine compartment which takes place only under load?

 

[hartv427]

Re: knock noise/stalls

I had a similar problem with my engine it had been running fine all of a sudden it wouldn't do over 2,700 RPM it fell flat on its face turned out to be a dirty a piece of dirt jamming the anti_siphon valve. You said it ran fine at low RPM mine did also. The noise coule be pre-ignition.

 

[Volphin]

Re: knock noise/stalls

Is the engine knocking too? Or just popping. Popping (backfire through the carb) could be a fuel restriction. Knocking would indicate internal engine damage. :facepalm:

V

 

[clasavi]

Re: knock noise/stalls

thank you for the replies. i will head to the marina and check out the fuel lines.

 

[clasavi]

Re: knock noise/stalls

well, i put the boat in the water and she ran fine on saturday. sunday i go back out and shortly thereafter sea tow has to tow me back to the marina. both of my batteries went dead. could the stalling i was experiencing before Saturday have had something to do with the not fully charged batteries?