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Mercruiser 5.0 running rough at idle

T

Todd Sabo

New member
Hi there,

I'm a newbie here and I have a 5.0 V8 305 carb and just took it out for the first time this summer. I started it up out of the water to warm it up for about 15mins and everything seemed fine. Got it in the water and was cruising around at about 35-40mph for a little while and then when I slowed down I noticed that something didn't sound right with the engine and it eventually died.

It started back up after a few tries, but when I put the throttle in gear it didn't start going like usual. It started to sputter and died again. I was able to restart and push the throttle forward much further than usual, it sputtered a little, but then finally kicked in and took off. It would run fine at a higher RPM for the rest of the day, but would run rough at idle or eventual die.

I'm assuming this might a fuel filter or carb issue. Not sure exactly where to start, but would appreciate any help.

Thanks,

Todd
 
What year engine and serial number? Is the spark arrester (air cleaner) clean or full of oily crap? Check/change the carb fuel inlet filter and any other filters. Take a look at the spark plugs to see how they are burning fuel/air mix...you want to see medium brown deposits on the plugs.
 
Thanks for all your feedback. I got around to replacing the fuel filter and no crud; spark arrester was full of oily crap, so I cleaned out with carb cleaner. Carb had some stuff on it where the spark arrester was so cleaned it off. Also sprayed some carb cleaner in. Plugs look ok, so I tried starting it up. It's having trouble idling. When I try to advance the throttle in neutral, the engine dies. Did this a couple of times with the same result. If I push the throttle almost full forward it will start, rev up high and then die.

No the boat was not put in storage properly last year.

Any ideas?
 
No the boat was not put in storage properly last year. It's having trouble idling.
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Carb choke functioning properly? What year and carb are you talking about? It probably needs a thorough cleaning.
 
I'll have to check the carb choke next. The year is 2000 and it's a Mercarb. Engine serial #0M079776. I'm going to look at cleaning it over the next day and see if that works.
 
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