1991 Force 70hp Exsessive Fuel Consumption

[Excalibur5]

Managed to fit the trim tab anode last week and took her out for a little fishing trip. Put 16 litres of fuel in which was already in cans on the boat when we bought her. Only went a few miles out and used half of the 16 litres so then just made it back to the boat yard! How many miles per litre should you expect from an engine of 70hp? We only throttled her up to 3/4 when we were out. Could it have been old fuel we were using that had lost its kick? Did i put too much two stroke oil in the mix?(Put 40/1 ratio in the tank) Any help gratefuly recieved.

 

[Justinde]

Re: 1991 Force 70hp Exsessive Fuel Consumption

Depends how far " a few miles' is. Depends on load, who was in the boat, prop ( pitch?), but ratio would make diddly squat difference. 16 litres aint much fuel but, by any stretch. I have a 30litre,15litre and a 20litre tank, and my 1988/125 goes for hours on 3/4 throttle on the 30 litre tank. I mean HOURS.

When I have my boat on a plane, I back off ever so slightly to maintain plane and increase mileage.

There are so many variables with fuel burn, unless you have a leak, it could nearly be anything.

I am assuming that the timing is ok and the link and sync is ok, and compression etc is all good.

Maybe post back with boat size/load and prop pitch?

 

[jerryjerry05]

Re: 1991 Force 70hp Exsessive Fuel Consumption

Justinde you keep this up and I can retire.Good reply.
Also you can check the fuel pump for holes in the diaphragm or leaks.
Like Justin said.You need to check the motor for WOT.
1-2 people 1/2 tank of fuel cooler,maybe a kid or dog(normal load).
Go for a ride and see what the motor revs to at WOT.
Should be 54-5500 rpm.
A wrong pitched prop can KILL your economy.
My boat has 17's I tried to get more speed and put on 19's and my fuel usage went up by 25-30%
I only got 3-4 mph with the 19's
16 liters that 4 gal?

Profile?Location? You might be close to someone who can help.

 

[Excalibur5]

Re: 1991 Force 70hp Exsessive Fuel Consumption

Hi guys we did three mile out and three mile back on 16 litres and used it all. boat is 18ft shetland kestrel. It may have been old fuel will get some more details from prop next time we go to the boat yard. moored in suusex england. Buy the way so grateful to you guys for your replies. Am sure pretty soon we will have this boat and engine running great with all your help

 

[pnwboat]

Re: 1991 Force 70hp Exsessive Fuel Consumption

18ft Shetland Kestrel. It seems like that's a pretty good size boat for a 70HP motor. More for cruising rather than water skiing? Like Jerry said, need to know prop pitch and RPM's. Fuel mix should be 50:1.

 

[roscoe]

Re: 1991 Force 70hp Exsessive Fuel Consumption

It could burn 24 liters per hour if held wide open.
12-15 liters at 3/4 throttle.


Another thing to check, and should be done as a maintenance item anyway, is the fuel pump.

The diaphram inside, can get hole, or tears.

When this happens, the fuel runs through into the crankcase, and is basically wasted.

Eventually, it will get bad enough to flood the engine.