Forum: WHALER
  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  90hp Johnson / 17 Montauk range

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   90hp Johnson / 17 Montauk range
fchristo posted 10-28-2004 08:47 PM ET (US)   Profile for fchristo   Send Email to fchristo  
I recently purchased a 1985 montauk with a 1986 90hp Johnson on it. So far, I'm a little concerned about the fuel consumption of the motor, given my tank is non-stock and only 19gal. In some pretty quick and dirty testing I've found that I burn 6gal/hr @ 3200rpm with a speed of 23mph. At 4000rpm I burn 11gal/hr with a speed of 30mph. Can anyone else out there with a 17 montauk and a 90hp Johnson tell me if this sounds reasonable?

The specs on newer 2-stroke 90hp Johnson motors show about 4gal/hr at 3200rpm and 7gal/hr at 4000rpm, which is a huge improvement. Could there be something wrong with my motor that is limiting my fuel efficiency? If this is the best I'm going to get with the motor I may consider repowering.

-fc

Freeport Alan posted 10-28-2004 09:00 PM ET (US)     Profile for Freeport Alan    
is the motor loop charged or cross flow ?
If it's a Spl model then I believe they were all cross flow induction, even if it's not a Spl it still may be a cross flow, cross flows were thirsty { but good } engines.
whalercop posted 10-29-2004 11:31 AM ET (US)     Profile for whalercop  Send Email to whalercop     
That sounds about right, maybe a little high. I have the same setup, only 87 newtauk and 88 90 johnson ex-vro. Bored .30 the last rebuild. There's a 27 gal pate tank and I can only imagine the range I could get with a 4 stroke. I like the v4's, with the exception of the vro's I think they were some of the best omc produced. They used the same design for alot of years, I also believe they produce more power than the newer motors, and weigh less. They are just thirsty. It is also very nice to be able to work on it myself, that is invaluable to me. Maybe rebuild your carbs and check the compression over the winter, that way everything is "tight" for next season.
2manyboats posted 10-30-2004 12:01 AM ET (US)     Profile for 2manyboats  Send Email to 2manyboats     
I owned the same year boat and motor you have and unless you were running in rough conditions , your numbers sound a little high. If range is the problem a larger fuel tank is the cheap fix. If fuel consumption is the problem and your gals per hr. are correct it looks like you would have to run 650 to 1300 hr. to break even on a new motor. ( I used $2.00 per gallon so if you pay more for gas it would not take quiet as long)
Peter posted 10-30-2004 09:29 AM ET (US)     Profile for Peter  Send Email to Peter     
I agree, the figures sound high and, if accurate, I think they indicate a problem. At wide open throttle (WOT) your 90 HP motor shouldn't burn much more than your horsepower rating divided by 9 or about 10 GPH. At 4000 RPM, approximately 2/3 throttle, and you are already exceeding the rate of fuel consumption for WOT.
jimh posted 10-30-2004 10:35 AM ET (US)     Profile for jimh  Send Email to jimh     
As Peter suggests, a seat-of-the-pants figure for fuel consumption in gallons-per-hour is about ten-percent of the engine's maximum horsepower when operating at wide open throttle. That is, 90-HP implies 9-GPH consumption at WOT.

Here is a link to a similar discussion and explanation in more detail:

http://continuouswave.com/ubb/Forum4/HTML/002038.html

In my experience, reports of fuel consumption are often understated by the boat/motor owner. The best way to find out how two boats compare in fuel consumption is for the owners to switch boats, and then buy gas for the boat they're running. This will eliminate any shading of fuel economy results.

Also, awareness of fuel consumption is directly proportional to price. When gasoline was $1.49/gallon (like it was in October of 2003 when I winterized my boat last season) you don't have as much concern about fuel consumption rates as when gasoline was $3.75/gallon (like I paid to those pirates on Beaver Island in Lake Michigan in 2001).

Re-powering with more a more fuel efficient motor will not always provide a return on investment, but a new motor will often increase enjoyment of boating. That is the whole point, anyway, isn't it? Have more fun, and get a new motor if you like. Or keep that older two-stroke running and just pay a little more at the gas dock each time.

masbama posted 10-30-2004 11:37 PM ET (US)     Profile for masbama  Send Email to masbama     
All I can tell you is I went down most of Mobile Bay today (and back) in search of fish with my '77 Montauk and a 2002 Johnson 90hp 2 stroke. I had about 9 gallons in one of my tanks and when I put it on the trailer it had one or two left. I ran about 3000-4000 rpms most of the way. Fuel consumption is NOT and issue with these engines. In fact, nothing is.
Bayoumontauk posted 11-01-2004 09:47 PM ET (US)     Profile for Bayoumontauk  Send Email to Bayoumontauk     
Your numbers seem a little high but close. I have a 96 Montauk with an 88 Johnson SPL and it drinks alot of fuel. I like to run a little fast because my runs are long and I burn 7-9 gph at about 4800-5000rpm. That's one of the rasons I am thinking about repowering with a 4 stroke or an optimax.
TightPenny posted 11-03-2004 12:03 PM ET (US)     Profile for TightPenny  Send Email to TightPenny     
I have been averaging a little less than 4 NMPG and around 4 GPH based since i put the 2001 90hp Johnson on my 2000 Montauk.

Most of my running is at 25-30 knots in the Barnegat Bay, and 15-22 knots out in the Atlantic.

The numbers are based on hour meter and actual fuel usage and GPS trip distances calculated by spread sheet. I'd post the actual numbers, but they aren't on this computer.

alvispollard posted 11-05-2004 11:16 AM ET (US)     Profile for alvispollard  Send Email to alvispollard     
Recent day's performance on '90 Montauk/'97 Mercury 100 2 stroke. Trolled for kings with '02 Yamaha 8 hp 4 stroke. 16 gallons used. 1 gal. trolling 6 hrs. 15 gallons running 44 miles (gps). 12 miles running to/from inlet WOT (40 mph). 3' waves slowed us in ocean to 15-17 mph speed. With 3 people and gear, boat , & motor (2500 # total). 44 divided by 15= 3 mpg. With 2 people and 1'-2' waves, I have gotten 4 mpg with similar driving pattern.
Blane posted 11-05-2004 12:55 PM ET (US)     Profile for Blane  Send Email to Blane     
The kicker is key!
rbruce posted 11-07-2004 07:41 AM ET (US)     Profile for rbruce  Send Email to rbruce     
Indeed this is an issue of planned obsolescence! The question is where is the point of equilibrium: should one "scap" a good used albeit gas hog Johnson V4 for an expensive brand new would be gas miser HPDI or four stroke?

Now, could it be that these Johnsons of yore where neglectful of the whims of the futures oil market and the deep pocketed speculators that roam its alleys? or could it be that the issue here is that the motor is not correctly tuned?

I get close to 2 gallons per hour with my Chrysler 20. Imagine that! What a gas hog!

Post New Topic  Post Reply
Hop to:


Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.