My 1978 70hp Johnson is a heavy drinker. Yours?

[jbo_c]

New to this motor. How much fuel should it take? Today I used 4ish gallons in an hour or so of full throttle use. Does that sound right? Jbo

 

[fireman57]

4 actually sounds on the great side. As a rule you will use 10% of your horsepower rating in gallons per hour at cruising speed. Usually about 3/4 throttle. So if you had a 70hp you will burn around 7 gallons an hour.

 

[jbo_c]

Thanks. Interesting rule of thumb I hadn't heard. I was actually thinking before supper that I could probably save fuel by going a little less than full throttle because I'm guessing that's a lot more fuel consumption with only a small increase in speed. I'm thinking between full and 3/4 throttle I only add 2-3 mph but likely a 20% or more increase in fuel consumption. I'm not in it for the speed as long as I'm on plane. 20mph or 30mph doesn't matter much to me. What's everybody else seeing? Jbo

 

[Bosunsmate]

yep i run about 3/4 throttle and get about 4.5 gallon per hour with my 82 60hp.
i figure its best at that throttle position as the first throttle movement is mostly timing changing on mine but the last throttle movement is all opening the butterflys further=more fuel

 

[emdsapmgr]

Bosun is right on the money. As you decrease the throttle from WOT, the first carb butterflys close slightly and you will lose a few rpm's. The spark stays at full advance. The trick is to decrease the throttle so that the butterflys close somewhat, but the spark stays at full advance. You'll maximize your fuel economy and lose just a few mph. 3/4 throttle is pretty close to that ideal point.

 

[canuckmark]

Mine's a 1978 85hp and is a heavy drinker too. Changing the prop made a huge difference for me in a good way - got the revs down.