120 johnson looper fuel consumption/cruising rpm

[suzukidave]

can anyone give a ballpark on fuel consumption for an 85 120 looper on a 19' mid to deep v? also, from a search it looks like wot is 5500-6000 but what rpm have folks found to be optimum for fuel consumption? can you run these down in the low 4000 rpm range to save gas or do they need to be kept near wot to keep'em happy?

these questions bear on two things. First, i'm looking at buying a 19' grady white with an 85 120 looper and an owner who is vague on fuel use. boat itself is nice and i was hoping to keep the motor for a couple of years until my wife/bank account recovers but this assumes it doesn't suck gas too bad. the boat weighs 2075 lbs without the motor. Second, i can also pick up an 87 120 looper with good compression very cheaply from a friend who has run it on a smaller boat for years with no tach or speedo or idea of gas usage (wish i was so carefree). i have to decide on the spare looper in the next couple of weeks as the friend's new motor is going on and i won't have time to figure out for myself how much gas the looper uses on the grady.

thanks for any help

 

[R.Johnson]

Re: 120 johnson looper fuel consumption/cruising rpm

That engine live's best at about 6000 RPM, that would be 12 gal. per hr. at full throttle. Cruising would be where the boat maintain's the best planing attitude. Here again, you will have to check out engine set-up first. Then select the prop for your need's.

 

[Silvertip]

Re: 120 johnson looper fuel consumption/cruising rpm

Fuel consumption at wide open throttle on any engine can be figured quite easily. Put a decimal point one position left in the HP rating. 120 = 12.0 gallons/hour. While that's a rough number, it is usually quite close. You need a fuel flow monitor, tach, and speedometer to determine the actual sweet spot (most fuel efficient) RPM for the engine/boat/load/ combination. It will likely be in the 4000 - 4500 RPM range however.

 

[suzukidave]

Re: 120 johnson looper fuel consumption/cruising rpm

thanks, so they are just as bad as a 70s 115 merc then :% darn, i always thought the loopers were more efficient.

 

[Silvertip]

Re: 120 johnson looper fuel consumption/cruising rpm

Better, but it still takes so much fuel to make so much horsepower. Go to Yamaha's web site and check performance tests on any boat and engine combination. Then compare two and four stroke fuel use. At wide open throttle the four strokes are not that much more economical. They have their advantage at mid range RPM.

 

[Walker]

Re: 120 johnson looper fuel consumption/cruising rpm

thanks, so they are just as bad as a 70s 115 merc then :% darn, i always thought the loopers were more efficient.

Yours is a big bore motor and more inches take more fuel.