Is there a better MPG carb for Mercruiser 120?

[Boatist]

Re: Is there a better MPG carb for Mercruiser 120?

Boat fuel mileage is best at a high idle, then as you increase the speed the fuel mileage goes down until the boat comes up on plane. As the boat climes up on plane then your speed increases with out advanceing the throttle. This point is usually your best mileage or cruseing speed. At this point advanceing the throttle will again start to decrease mileage. At or near WOT RPMs with full throttle will be your worst mileage. So you need to decide if you want good mileage or higher speed.

Another thing that affect mileage a lot is the boat weight and type of hull. The deeper the V the more fuel you will burn but you gain a softer ride. Flat bottom good for fuel mileage but a rough ride.

Going up in prop pitch is just like shifting into over drive in your car and you will get better mileage. However need the stay in the WOT RPM range. The car will down shift if you go wot but if the prop pitch is too high the engine will be lugging and you can burn a pistons.

Many car today are running 65MPH at just 2000 rpms in over drive.

Going down is pitch is like shifting your car to a low gear. You will get faster hole shot use more gas and if too low a pitch can over rev the engine and shorten it life.

 

[woodrat]

Re: Is there a better MPG carb for Mercruiser 120?

I finally found the numbers on the prop that I have. It is a 15 by 17. the next one up in the Michigan line is a 14 1/2 by 19. I'll try that one and use your tips about engine rpms and see if I can do better. Also going to put the kicker on it's own tank so I can see how the big engine does alone. Hopefully will get out in the ocean this next week again and maybe the weather change we've been having has brought the fish in closer.

Thanks!