1975 233 hp 351 ford mercruiser running rough after water/fuel contamination

[soulsalvation]

started season off well with an engine that ran beautifully until we hit water in the tank,episode out on the lake getting back to shore assisted by Coast Guard, at first big stall then trouble getting going ,boat ran well on and off then we decided to head in and call it a day took out 12 litres!, obviously a bad purchase at that amount. So yesterday we wanted to go out and prestarted at home to make sure all was well...and it wasn't, engine had trouble starting, conked out but after a while began to run steady but rough, and we noticed black smoke(poor ignition) and peculiar metallic vibration sound between 1500-1800 rpm but goes away above that...long story short could this be coincidental bad ignition plugs,rotor cap or something more insidious...I'm hoping engine wasn't damaged by the water content. There's no blue smoke, just what looks like engine not burning properly...she's responsive but not smooth. Praying for an encouraging answer. The ignition system is 7 years now but low hours(and no operation between 2008-2009) so I wasn't suspecting any problem at that level. Thanks for help.

 

[alldodge]

Re: 1975 233 hp 351 ford mercruiser running rough after water/fuel contamination

Welcome to the forum

Let me start by rephrasing your statements and correct me if I misunderstood

Engine running good until this year after getting gas and being towed in by Coast Guard. later found 12 liters on water in gas tank.

Next day started engine at home ran ok but rough, noticed black smoke and a metallic sound around 1500-1800 rpm but goes away above that.

Currently not running smooth but does ok, just not running correctly.

That being said and I will offewr the following:
12 liters of water found in gas would also lean me to thing the gas you have is bad. If all that is gone then not to worry. Water trying to be used in a gas engine will not damage a gas engine only a diesel.

Suggest check and/or replace plugs, cap, rotor and fuel filters. It appears to be more an ignition issue and maybe a lot of sitting and mosture build up """ That is if the bad gas is gone """.

 

[Bondo]

Re: 1975 233 hp 351 ford mercruiser running rough after water/fuel contamination

started season off well with an engine that ran beautifully until we hit water in the tank,episode out on the lake getting back to shore assisted by Coast Guard, at first big stall then trouble getting going ,boat ran well on and off then we decided to head in and call it a day took out 12 litres!, obviously a bad purchase at that amount. So yesterday we wanted to go out and prestarted at home to make sure all was well...and it wasn't, engine had trouble starting, conked out but after a while began to run steady but rough, and we noticed black smoke(poor ignition) and peculiar metallic vibration sound between 1500-1800 rpm but goes away above that...long story short could this be coincidental bad ignition plugs,rotor cap or something more insidious...I'm hoping engine wasn't damaged by the water content. There's no blue smoke, just what looks like engine not burning properly...she's responsive but not smooth. Praying for an encouraging answer. The ignition system is 7 years now but low hours(and no operation between 2008-2009) so I wasn't suspecting any problem at that level. Thanks for help.

Ayuh,... Welcome Aboard,.... I'd think a Tune Up, 'n Service is overdue at 7 years,...

Sounds like many problems, 'n the tune up, 'n service will point out the Suspects,...

Throw in a Compression test, 'n you'll pretty much know the health of yer motor,...