1984 Johnson 85HP Drinking Fuel

niceandeasy

Seaman Apprentice
Joined
Jul 5, 2013
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32
I just got a 15' tri hull boat with a 1984 johnson 85HP on it. I took it out for the 2nd time yesterday and burned 9gal in about 2 hours at 3/4 throttle most of the time. dont know alot about the motor and the propeller is a 19X13. my friends boat was with me with a 80's model 70hp johnson on a 17' tri hull can out run me and burns 1/2 the gas.
 

Solittle

Fleet Admiral
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Apr 28, 2002
Messages
7,518
Re: 1984 Johnson 85HP Drinking Fuel

Rule of thumb - fuel burn = 10% of hp at WOT. So 85 hp = 8.5 gph at WOT - 2 hrs = 17 gal at WOT - you ran at 3/4 throttle so I would say you be doin good. Those V-4s love fuel. On comparing with another boat - lots more into it than hp.
 

82rude

Rear Admiral
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May 8, 2012
Messages
4,082
Re: 1984 Johnson 85HP Drinking Fuel

what are your rpms with that prop.im assuming its a 13x19p prop.you could be lugging the motor or possibly over reving .need to know your rpms at wot to help.
 

niceandeasy

Seaman Apprentice
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Jul 5, 2013
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32
Re: 1984 Johnson 85HP Drinking Fuel

Don't know the rpm's and don't have room for a gauge. And what does wot stand for?
 

pn

Petty Officer 1st Class
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Apr 20, 2013
Messages
374
Re: 1984 Johnson 85HP Drinking Fuel

if there's excessive smoke or fuel spewing from the carb, might be 1. broken reeed valve, 2. hole in your fuel pump diaphram or 3. float bowl needle that stays open dribbling fuel down the manifold. good luck.
 

niceandeasy

Seaman Apprentice
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Jul 5, 2013
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Re: 1984 Johnson 85HP Drinking Fuel

There is no smoke but come to think of it there is fuel/oil on the trans.
 

bonzoscott

Senior Chief Petty Officer
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Jul 26, 2008
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745
Re: 1984 Johnson 85HP Drinking Fuel

WOT is wide open throttle. I'm not sure if over pitch on the prop would consume more fuel, but I had 15' tri-hull with an 85 hp and I found a sweet spot with 14 dia. 17 pitch prop. You need a tachometer and find your prop by achieving 5500 - 5800 RMP at WOT. Another variable is: Did you have 7 people on the boat?
 

niceandeasy

Seaman Apprentice
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Jul 5, 2013
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32
Re: 1984 Johnson 85HP Drinking Fuel

Come to find out the boat motor is a 74' it was titled wrong year some how. And there was 2 adults and 2 little kids on boat maybe 450lbs.
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: 1984 Johnson 85HP Drinking Fuel

Your fuel usage sounds cometely normal. Your friend's 70 is a loop charged design and is much more efficient.
 

gm280

Supreme Mariner
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Jun 26, 2011
Messages
14,585
Re: 1984 Johnson 85HP Drinking Fuel

It is always hard to make honest statements about one boat/engine over another without knowing a ton more details. How old are the two boats? Does your tri-hull have soaked wood/foam now making it so much more heavier? What is the total weight of each setup? What is the type props of each? Are both props made from the same material and in new condition? Are the two setups equally adjusted for maximum efficiency with their engines setting at prop height and setback? And the list goes on and on... Just that fact that there are both tri-hulls and their lengths are certainly not enough... Now if you swapped engines and did another comparison, then you have some data to work with. Your tri-hull could be soaked with possible rotted wood in it's structure and even the foam over the years and not basically know of it making your boat so much heavier... JMHO!
 

wayneo99

Petty Officer 2nd Class
Joined
Oct 14, 2005
Messages
151
Re: 1984 Johnson 85HP Drinking Fuel

I have a 1983 115hp fast and strong but drinks alot of gas, so did my 85hp but not as much as the 115
typical for cross flow V4s.
 

niceandeasy

Seaman Apprentice
Joined
Jul 5, 2013
Messages
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Re: 1984 Johnson 85HP Drinking Fuel

Looking up the boat it's saids it's 700lbs empty max hp is 70 for the boat.
 

82rude

Rear Admiral
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May 8, 2012
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Re: 1984 Johnson 85HP Drinking Fuel

Looking up the boat it's saids it's 700lbs empty max hp is 70 for the boat.
my last boat said just over 1000 for weight.when I took it to the scrap yard the boat alone weight in at 1950 lbs!!!!so it had over 900 lbs of soaking wet foam .
 
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