Merc 3.0 running rich?

[beason]

I have the 4 cyl merc 3.0 in my 17ft boat and burned an entire 22 gal tank in about 9 hours of lake time. (not all running, but probably 80%). I can smell gas fumes at low speed, it idles rough, and if i dont let it idle for 5 seconds or more after throttling back to neutral before shutting it off, it will diesel, and knock.

Does this sound like a rich condition? If so, does anyone know how, or have documentation on how to adjust the carb? I downloaded the service manual for the boat, but I would like to have some personal experiences before diving in.

 

[Bondo]

Re: Merc 3.0 running rich?

Ayuh,... It sounds rich...

Rebuild the carb, 'n reset the internal settings...
Probably the float setting, but who knows til ya tear it apart...

 

[beason]

Re: Merc 3.0 running rich?

any info on how to go about doing this? I was told it was rebuilt last year, so maybe its just an adjustment needed.

Thanks

 

[LilRedNeckGirl]

Re: Merc 3.0 running rich?

a 4cyl engine at full load burns how many gallons per hour? you say 9 hours, 80% run time, so apx 7.5 hours running? Im guessing water sports so high rpm, heavy load. IF, you burn 3 gal an hour, thats your tank full in 7 hours. You may have other issues related to the after run and gasoline smell, but im thinking your consumption ratios are near where they should be. Your options for 9 hour days on the water may best be solved with a bigger tank.... nPersonaly, I wont leave the dock without topping off my 100 gallon tank.....
AE; I run twin 3.0's. (140 horse mercruisers} 30 gallons gets me about 5 hours of run time with both running at 3000 rpm. ( apx 80 ~100 miles over the weekend) twins run at a lighter load as two props are pushing the boat. factor in no major chop or waves, just an empty boat on plane in calm river conditions. be glad your running a 3.0, as bigger engines are measured often , in gallons per mile.......
Another check is your prop. Right pitch? good condition?
Then examine your habits. are you cruising at a reasonable speed on plane or are you running full slam wide open? Lots of factors influence your consumption rate. And just a fyi, running wide open heats up an engine, which could lead to after run and gasoline smells when you stop.

 

[beason]

Re: Merc 3.0 running rich?

it was over 2 days. the first day was 6 people in the boat and dragging the tube all over the lake and burned about 3/8 tank in 5 hours. the next day was 4 people and some tubing and kneeboard attempts for 4 hours that ran me almost dry. I guess i just have to fill up before every outing.

I have the 19pitch power prop on the boat, and i almost never run wide open, mosty just up on plane and cruse. the lake was very choppy both days so maybe that was an issue.

I am still concerned about the dieseling at shutdown, and the rough idle.

thanks for the info!