Fuel consumption 1977 Evinrude 70 hp outboard

[Bubbasboat]

I have a 1977 Evinrude 70 hp outboard motor. The motor is running smooth and is totally responsive. There is no excess fuel smell during operation, as in raw fuel. I am currently using about 2 gallons of fuel per hour. Seems high to me. Can I reduce this in any way without effecting performance.

Or can someone tell me if this is normal for this motor?
I just bought the motor this spring.

 

[glenn property of pam]

rule of thumb is 1 gallon per 10hp at wot.

so 70hp = 7 gallons per hour at wot

so 2 gallons a hour means your not pushing the lever far enough forward

 

[Bubbasboat]

OK, not quit the answer I was expecting, use more fuel!

I am pushing the lever as far forward as it will physically go.

Sounds like a throttle cable and idle adjustment.

Thanks for the unexpected but appreciated info!!

 

[UncleWillie]

Unless you tend to travel well more than 30 miles at a time,
2 gal per hour may indicate that you do not run at WOT for all 60 minutes of the hour.

My 220hp engine shows 16 gph at WOT on the fuel flow meter.
But, I average about 3.5 gph overall as WOT is not used all that much.

 

[Bubbasboat]

The time I went out was specifically for the purpose of running the motor at wot. Was the first time out after I installed motor. Lake is large enough to keep speed up at all times. I left no wake zone at harbor and opened it up, slowed 4 times to change driver, ran for 3 hours until my 6 gal tank ran empty. Tank was positioned to use all but 1 quart of fuel content. Yes, I had reserve on board! HA HA

 

[roscoe]

2 gallons is unthinkable. Wish I could do that.

Maybe more info would help.

Size, make, model, aluminum or glass boat?
WOT rpm you are running at?
Speed you are getting at WOT?


My 50 can use 4.5 gallons per hour.
My 75 uses a little over 6 per hour.
My 115 goes through 8 gallons per hour at 4000 rpm. (wot is 5600).

My 5 hp troller, uses about 1 quart every 3.5 hours.

 

[Bubbasboat]

1977 Evinrude 70 hp outboard. 1974 16 ft Glasspar V165 hull, weight 990, motor weight 212lbs, RPM unknown as tach is not working. My speed at WOT is 23 mph. I had three people on board during test run as well as 5 extra gals of fuel reserve.

I going out again tomorrow, hoe to get Tach working, not sure why its not.

Maybe I should be happy with 2 gph looking at your 75hp at 6 gph.

 

[Stumpalump]

That boat should be in the 30's with that engine.

 

[UncleWillie]

That boat should be in the 30's with that engine.

+1
The speed is lower than expected.
Not only is 2 gal per hour unusual, so is the 11+ miles per gallon.

What prop is on the motor?

 

[H20Rat]

I had nearly the exact same setup... Speed should be mid to even high 30's on a good day with a light load and trim up.

 

[Bubbasboat]

What prop is on the motor?

13 3/4 X 15 Aluminum

 

[UncleWillie]

13 3/4 X 15 Aluminum

Assuming a 2:1 gear ratio and a 6000 rpm WOT; A 15 pitch prop at 23 MPH would have a 46% slip!
A modest 7% slippage would put you nearer to 40 mph. No slippage yields a theoretical 43mph.
There is no reason not to be in the upper 30's.

The physics behind 2 gph indicates you are only producing 20 hp, and ~3500rpm, not 70hp at 6000rpm.!
Something is seriously amiss.

The good news is that once you get all 70 hp and 40mph at ~7gph, you can always throttle back to 23 mph and get your original 2 gph again.

 

[iggyw1]

13 3/4 X 15 Aluminum

I have a 16 ft fiberglass 1965 Geneva with a 75 HP Evinrude 1965 model on her. I am using more than double the gas you are using at WOT for an hour. I would use up a 6 gallon tank in an hour at wide open the hole time. I am getting about 34 MPH on my speedometer (not knowing how accurate that is) and I have no tach. I would be real happy with two gallons per hour WOT. That is impossible it would seem.

 

[Bubbasboat]

Fortunately and unfortunately my fuel consumption question has been answered. I am in fact in the 6 or so gallon per hr usage range. 2 felt better! HA HA

Still working on the speed. Just not getting what I'm told I should be. Consensus seems to be 35.

 

[metriccrescentwrench]

Still working on the speed. Just not getting what I'm told I should be. Consensus seems to be 35.

Are you going by the speedometer or a gps? A lot of things can be wrong with a speedometer to give you an inaccurate number, including a partially plugged pitot, leaking tube, or problems with the gauge itself.

 

[Bubbasboat]

I have been using the speedometer on the boat, Pitot, tube good and clear. May be the speedo itself. I am going out next time with gps. Waiting for power jack to arrive.

 

[glenn property of pam]

check the butterflys in the carbs are opening fully. when I first got mine the cable was badly adjusted so the carbs only opened 50%. Not sure if someone done this by mistake or to restrict the top speed.

 

[nickcunn]

I have a 25 hp mariner on a 1971 glasstron v156. I use a little over a gallon and hr. at 14 mph. I believe I should be in upper teens closer to twenty. I have everything adjusted right. Not sure whats going on. Now my mechanical fuel pump was broke so I replaced it with an inline fuel pump.

 

[metriccrescentwrench]

I have a 25 hp mariner on a 1971 glasstron v156. I use a little over a gallon and hr. at 14 mph. I believe I should be in upper teens closer to twenty. I have everything adjusted right. Not sure whats going on. Now my mechanical fuel pump was broke so I replaced it with an inline fuel pump.

Did you have a question? (If so you'd probably get more help if you started your own thread.)

As far as the electric fuel pump, that's not the greatest idea on a 2 stroke engine.... if something bad happens the pump will keep pushing fuel to the engine and feeding the flames. Electric pumps are used in racing, but those guys are mandated by the rules to shut the pump off with their safety kill switch.

 

[nickcunn]

I was just making a statement like everyone else on fuel consumption for a motor. no questions. I have plenty of threads over the years.