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1977 Evinrude 70hp Fuel Consumption

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Evinrudebigtwin35

New member
I was wondering what the fuel consumption of my 77 Evinrude 70 engine should be. It has 145 PSI in all three cylinders, new water pump, spark plugs and idles and runs smooth in all throttle ranges. Its mounted on a 1985 15' Henry O McKee Challenger (Boston Whaler Clone) Myself and one passenger and two six gallon tanks of gas. Results were that I burned about six gallons per hour at 3/4 throttle on flat water. I checked the plugs after the last outing and they were even brown in color. No wet plugs. The plugs from cylinders 1,2 and 3 all looked the same. If this is good I am going to bump up to two 12 gallon tanks soon.

Thanks
Tony
 
Re: 77 Evinrude 70 Fuel Consumption

6gph sounds a little high. Sounds like the plugs are the right color and the engine is running properly though. 145 psi sounds a bit high to be running regular gas on. Have the heads been shaved or any performance mods done to the powerhead? Is your gauge accurate? Most experts recommend premium above 140psi compression.
 
Re: 77 Evinrude 70 Fuel Consumption

6gph sounds high to me.
dcramer is right about the type of fuel you are useing for 145 psi
 
Re: 77 Evinrude 70 Fuel Consumption

On a 15' rig, 6 gallon of fuel should run that 1977 70hp Evinrude for approximately 1hr & 45min..... at crusing range.

Assuming that compression, spark, carburetion is as they should be.......

Crusing range is set by obtaining full throttle then backing off approximately to 3/4 throttle. This sets the spark advance to full BUT closes down the throttle butterflies considerably.

NOTE: Simply going from a throttle idle setting up to 3/4 throttle doesn't do it..... full throttle must be obtained first.

YOu can get a ghood idea of what I speak by having the hood off, engine not running BUT in forward gear, then watching the spark and throttle linkages while obtaining full throttle..... then backing off somewhat.

When backing off, notice when the spark advance just starts to move back.... that is the point referred to as "crusing range" (notice hown much the throttle butterflies closed?)...... Of course you do not want that spark advance to move back at all, I was just making a note of where that point is.

Let us know if this makes any difference.
 
Re: 77 Evinrude 70 Fuel Consumption

Joe, I think I am close to that 6 gallon per 1 3/4 hour rate. After talking to my son and wife they corrected me as to how long we were out. As far as operations go, I always reach full throttle then back off to cruise at 3/4. Thats how I always run my 58 Bigtwin 35 too. When I checked compression it was before I started it for the first time after having set for 15 years. I gave each cylinder a light spray of oil first then rotated the flywheel by hand. I then cranked it with the starter to check the compression. I'll try one now at normal operating temperature. I am the third owner. The second owner never used it much in the 20 years he owned it. He was not aware of any problems when he bought it. It is very clean and shows no signs of having been rebuilt. The head has never been off as the factory paint still bridges the head gasket. I'll take it out later this week and watch the linkage. I'll let you know.

Thanks
Tony
 
Re: 77 Evinrude 70 Fuel Consumption

Rule of thumb - a motor will burn (in gallons) 10% of it's horsepower at full throttle.

As Joe points out, you can cut that number in half by finding your "cruise speed".

So if you have a "two speed motor - idle and full throttle" expect to burn upwards of 7 gallons per hour at wide open with a 70 horse model.

Despite all the claims of newer motor (particularly 4 strokes) of how much more fuel efficient they are, at WOT the rule of thumb still applies. On water tests consistently show that a brand new 150 (for example) still burns 15 gallons per hour at max rpms, just like it's carb model predecessor did in the mid 1980's. It's at lower rpms, generally below 3000 where they are far more efficient...
 
Re: 77 Evinrude 70 Fuel Consumption

I checked the linkage as Joe suggested after work tonight. The linkage is working correctly. I moved the trottle to WOT and both spark advance and trottle were full. As I backed the trottle down to about 3/4 the butterflies closed partially while the spark advance remained full advance. I like this motor as it seems pretty simple like my 35 with the exception on the power pack CD ignition. I will not get the chance to do any long runs until this weekend but a few short trips for fishing after work this week are in my plans. I'll let you know how I made out.

As always thanks for the help
Tony

Thanks for the replies
Tony
 
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