'74 Merc 1150 115hp Idling Issues

[capn kurt]

Hi guys,
I've got an issue with my inline 6's idle quality. I am able to easily start the motor using the choke and idle up lever. It always starts; however, sometimes when I return the idle up lever to normal the motor will stall, other times it will idle perfectly. Doesn't seem to matter what the motor temp or the ambient temp is when this happens. Sometimes after an hour or so of constant cruise it will idle perfectly when coming in to dock, with a nice, low idle that doesn't jar the driveline while shifting. Other times, it stalls and I have to use the idle up lever to keep it running at a higher rpm until I can quickly get it into gear (with an obvious driveline clunk) and give it throttle to move out.

The Compression is good, gas is fresh, and it runs perfectly otherwise - great holeshot, and no lags or hiccups at any point in the rpm range. The boat sat for about two years without use before I got it, with stabilizer in the fuel.

I'm new to boats and was wondering what you all thought that I should check first?

 

[aussieflash]

Re: '74 Merc 1150 115hp Idling Issues

Your idle may be a little low.Check revs in water and just in gear and make sure it's in spec range as per Merc manual.Your carbs/ jets may need a clean.

 

[Texasmark]

Re: '74 Merc 1150 115hp Idling Issues

The intermittent part is what concerns me. I have increased my idle speed from the 675 in gear that my manual recommends to keep it from doing what yours does (continuously). The rubber hub in the prop absorbs the shock if you don't get too carried away with rpm's.

Might run a can or two of Sea Foam in the next couple of fill-ups. Cleans carbs and combustion chambers. I use it all the time.

Mark

 

[capn kurt]

Re: '74 Merc 1150 115hp Idling Issues

Thanks, guys.

Okay, I'll do the Sea Foam right away - is this comparable to a de-carb? If that doesn't solve it I will be pulling the carbs and doing a re-build.