90hp 1986 Johnson peak fuel efficiency

[fchristo]

Recently bought a used 90hp 1986 Johnson VRO (the oil side of the VRO pump has been disabled, I mix 50:1) and was wondering what reasonable fuel efficiency was for this motor at various rpms. At what rpm does peak fuel efficiency usually happen? When running at about 4000rpm I seem to be consuming 10-11gal/hr, which seems pretty high, but I'm also used to my little 15hp four-stroke. <br /><br />Thanks,<br />FC

 

[fireman57]

Re: 90hp 1986 Johnson peak fuel efficiency

WOT is your highest fuel use. Usually around 2/3 to 3/4 throttle is your best. You should be able to hear and feel your engine if it is lugging or screaming. My '91 25hp uses about 6 gallons in three hours at WOT. If your 90 would fit on my small boat I's swap you.

 

[dolluper]

Re: 90hp 1986 Johnson peak fuel efficiency

10 gallons per hour is high my old 85 uses about 5 gallons in an hour going 4500 to 5200 rpm hum maybe old is good check out your plugs!

 

[fchristo]

Re: 90hp 1986 Johnson peak fuel efficiency

Wow, I would be ecstatic if I could get that type of fuel efficiency. I take it your motor is a 90hp, 4 cylinder as well? Sorry if this is a dumb question, but what's the rationale for checking the plugs?

 

[phatmanmike]

Re: 90hp 1986 Johnson peak fuel efficiency

if the plugs are fouled, they aint getting the propper spark, and there for not burnig as hot or propper as they should, and there for you experience a power loss, and therefor......<br />..<br />..<br />..<br />.<br />..<br />.<br />.<br />.<br />.<br />.a witch!!!!!!

 

[piers]

Re: 90hp 1986 Johnson peak fuel efficiency

I thought I read a rule of thumb somewhere that said you take half your total H.P. i.e. if yours is a 85 then use the figure 4 for aprox.(4.25 to be exact) then add 2 gph for each engine you have.So at the most eff. RPM for your boat set up your fuel burn should be somewhere around 6-7 GPH.It seems to work for my boat but I don't have a fuel flow guage to know for sure.That is going to be my next purchase for all kinds of reasons and fuel costs being the bigest one.I am running twin 150's and being at that sweet spot can make a huge difference.<br /><br /> PT

 

[Tolly family]

Re: 90hp 1986 Johnson peak fuel efficiency

You have something wrong, my brother and I have the 90 and 115 and they burn about 8gph at 4500. What is your max RPM? Mine is 5500.<br /><br />Dan

 

[piers]

Re: 90hp 1986 Johnson peak fuel efficiency

FC<br /><br /> I forgot to say in my rule of thumb to first divide your total H.P. by 10 then chop that figure in half and add 2 GPH per eng. for the expected burn at your most efficient RPM.Sorry its been a long day.<br /><br /> PT

 

[fchristo]

Re: 90hp 1986 Johnson peak fuel efficiency

Dan -<br />My max RPM is 5500 as well. I think my motor would guzzle about 13gal/hr at 4500rpm... What year is your 90hp? <br /><br />FC

 

[Tolly family]

Re: 90hp 1986 Johnson peak fuel efficiency

My 90 is a 87 on a Montauk and my brothers 115 is a 91 on a Montauk. I have heard that an outboard burns 10% of its HP rating at full throttle. Are you using US gallons? <br /><br />Dan

 

[dolluper]

Re: 90hp 1986 Johnson peak fuel efficiency

Hay sorry to confuse you guys but I was thinking as a canadian 5gal can is 6 something u.s.a and it's and old 85 hp Johnson

 

[JC1933]

Re: 90hp 1986 Johnson peak fuel efficiency

Hi guys no more confusion.1 gal,US is 0.8326742 UK gal, 1 UK gal, is 1.2009499 US gallon. You all have anice day. J C.

 

[fchristo]

Re: 90hp 1986 Johnson peak fuel efficiency

Dan --<br />My motor is on a Montauk as well, and I'm talking US gallons. Sounds like I may have an issue if you're really getting 8gal/h @ 4500rpm. <br /><br />FC

 

[ledgefinder]

Re: 90hp 1986 Johnson peak fuel efficiency

Those crossflow V4s burn a TON of gas, if you're used to a smaller motor, and I've never found an rpm that really reduces the consumption. Your usage sounds about right to me. The 50/56 cubic inch triples (60-70hp) do a lot better.

 

[Tolly family]

Re: 90hp 1986 Johnson peak fuel efficiency

I did a search over on the Whaler web site and there is a lot of info on mileage. Most people with Montauks and 90-115 2 strokes are claining 4-5 MPG at cruise which is right on with my numbers. Labor day weekend i ran from Port Ludlow Washington to Port Townsend and back with 2 adults 2 kids a 6hp kicker and 24 gallons of fuel, the trip was 32 nautical miles and we burned 9 gallons for an hour and 5 minutes of cruise (my wifes mascara was gone by the time we got home).<br /><br />Dan

 

[fchristo]

Re: 90hp 1986 Johnson peak fuel efficiency

Dan, what year is your 90hp?<br /><br />-fc

 

[funpilot]

Re: 90hp 1986 Johnson peak fuel efficiency

I burn about 5-6 USgal per hour crusing with my 1990 90hp V4, more when I'm pulling skiers.<br /><br />Dan... I used to have a 1952 Tollycraft Utility with a 1963 Mercury 45 hp on it. I loved that boat! (sorry for the threadjack)<br /><br />fp