why is my motor using up gas way to fast

[bfensom]

I have a 75 mercury fourstroke efi and it ran out of gas from a full tank in about 20-25 mins tops. I didn't see any fuel in the water and couldn't smell it either. My friend has the same motor on his boat just its a 90 on a bigger boat and his needle barely moved. What kind of problems could be happening?

 

[Scott Danforth]

Magic Carnac says.....

Since none of us have psycic powers
What kind of boat? Is the motor set up correctly? What speed were you running? A 3 gallon tank or a 30000000000 gallon tank?

 

[bfensom]

Its an 07 legend exterminator with a 75 merc fourstroke efi... I had it running at 5500 rpm max and I used to for 20-25 mins tops going from the boat launch, to 2 fishing holes then back to the launch. I just had the boat in to my mechanic 3 days before I went out and he said the motor was running fine and was in great condition. The tank is a 6.6 gallon as well. It makes zero sense, but it happened and I was just wondering if anyone had any insight as to why.

 

[MTboatguy]

Have you checked to make sure the choke is not hanging a small amount on it, I have had that happen, which cased high fuel consumption.

 

[GA_Boater]

Did you start with a full tank or an almost full tank?

 

[roscoe]

Did you fill the tank before you took the boat to the mechanic, or after you picked it up?

Took a motorcycle in with 4 gallons, picked it up with a pint.

 

[bfensom]

No I never even thought about the choke actually. I'll have to check that out... And ya the tank was topped right up full. Someone mentioned the air valve on the tank lid being shot.. Could that cause it to use more fuel?

 

[MTboatguy]

I would expect it to be low on power or maybe even quit at WOT if the vent is messed up on the tank, because it would starve for fuel with a plugged vent. Take a good look at your choke, I have seen it happen more times than you would imagine, I towed a guy back to the dock a couple of years ago, who ran out of gas and when we got it back to the dock pulled the hood, one of his carbs the choke plate was partially closed.

 

[Alumarine]

If it's EFI it won't have a choke.
Running it at 5500 rpm will impact fuel consumption.

 

[Scott Danforth]

Its an 07 legend exterminator with a 75 merc fourstroke efi... I had it running at 5500 rpm max and I used to for 20-25 mins tops going from the boat launch, to 2 fishing holes then back to the launch. I just had the boat in to my mechanic 3 days before I went out and he said the motor was running fine and was in great condition. The tank is a 6.6 gallon as well. It makes zero sense, but it happened and I was just wondering if anyone had any insight as to why.

you went 25 minutes at WOT from the boat launch to the fishing spot. then WOT from fishing spot back.

the data per http://www.boat-fuel-economy.com/mercury-outboard-fuel-consumption-us-gallons has your fuel usage at WOT at 7.6 GPH. you ran aprox 50 minutes at WOT and went thru 6 gallons of fuel. (7.6 gallons x 50/60 = 6.333 gallons)

back off the throttle. nothing wrong with your motor.

 

[bfensom]

Your 100% right Scott this is from a test Mercury had done on the same motor as mine with a similar sized boat. I think I'll keep her humming around 3500 for now on lol... Thanks for the help guys

 

[MTboatguy]

If it's EFI it won't have a choke.
Running it at 5500 rpm will impact fuel consumption.

Sorry, guess I skipped the EFI notation, I guess us old guys think older....

 

[Alumarine]

Sorry, guess I skipped the EFI notation, I guess us old guys think older....

I do the same thing all the time. I still think all I/O's have points.