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Rough Idle

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sullybe

Contributing Member
I have a Merc 115 hp 1978 that

I have a Merc 115 hp 1978 that runs rough at idle and seems to use a lot of fuel. Runs great at high speed but still uses a lot of fuel.Anyone have any ideas on how I can improve fuel and idleing??
Dan
 
"At full throttle you should b

"At full throttle you should be burning about 10-12 gallons per hour - that is NORMAL.

These are gas pigs just like every other outboard out there.

The rough idle could be due to, varnish/clog forming on the low speed carb jet, old plugs, carbs out of adjustment (although they almost never go out on their own), old gas (gas that's 2 weeks old is OLD).

Only way to improve fuel economy is get a smaller motor. For all the advances that have been made an 1970/80 something 115 burns 10-12 gallons per hour. A new 4 stroke 115 burns 10-12 gallons per hour ditto Merc's Opti's and Evinrudes ETEC's.

Stay light on the throttle, consumption drops by over 50% if you use no more than about 3/4 throttle - every motor has a sweet spot usually somewhere between about 3200-4500 rpms (depending on the motor) - you just have to find it..."
 
"Thanks for the info Graham, I

"Thanks for the info Graham, I ran 2 tanks with high octain gas and Sea Foam thru the motor and it seems to idle much better. I don't have a tack but the sweet spot is like you said about 3/4 throttle.

Thanks Dan"
 
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