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This was my second voyage on my 1988 montauk 17 with same year Johnson 90 & the tempo metal tanks. I ran them both dry in far less than a full days boating & although I was operating under full power most of the day does this seem right? It was my belief that with this being a fairly seaworthy boat it would be better equipped to travel long range without stopping to refuel. It appears to be running fine & the sparkplugs seem to be burning properly with no smell of unburned fuel present but I am litterally looking around to see if I'm actually burning all that fuel or is it leaking somewhere? Something doesn't seem right here, all seems to be functioning well & it is equipped with a remote auto lube injection unit but all seems fine there to. Any comments or advice would be appreciated because I certainly don't want to be worrying about running out of fuel anywhere! thanks, Darren

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Darren:

I need more information. Specifically, when you're "running"... how are you running (i.e. speed, water conditions, #passengers, gear, size of Tempo tanks, etc.)?

i'm on a lake about 12 miles long. When I fish for 6 hrs or so... over 5 or 6 spots round the lake.... travel on plane but not WOT.... with 2 on board.... I might go through 5 or 6 gallons on my Evinrude 90hp.

Mike

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If I remember correctly the older two-stroke 90's averaged 3.5-4.5 mpg at cruise and much less at wide open throttle. So if each of your tanks holds 6 gallons you have 12 gallons of fuel multiply that by mpg 3.5 = 42 miles. Not very far. To put it another way if you are running the boat at 20 mph then 42 miles is a little more than 2 hours of run time.

But don't take my word for it.

To determine your MPG Miles Per Gallon
Get out a GPS and set the trip odometer to zero also note the time you leave the dock.
Go for a 30 minute run and make sure you run the boat at YOUR normal speed(s).
When you get back to the dock check the distance you travelled on the GPS and write it down. Now go refill the tank you used at the gas pump and note how much fuel was consumed.
To get your MPG figure take distance traveled (from the GPS) and divide by fuel used.

To determine your Gallon Per Hour rate (GPH)
If you ran for 30 minutes then double the amount of fuel consumed.

To determine your safe travel distance:
Multiply your total fuel capacity times MPG divide that number by 3.
The rule of thumb is one third out, one third back and one third in reserve.

If you need to travel farther than your capacity currently allows then buy a bigger gas tank or buy a motor with better fuel economy or both.

I run a 20 gallon tank myself.

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see the above post. acknowledge the fact that your boat has a sweet spot for running and unless you get a fuel flow meter and connect that to test, that you will only be approximate.

in my boat, idling burns a lot of fuel - idle speed up to plane. then over a certain RPM it's a hog too. i calculate i have about 7o miles capacity with my current 20 gal tank. moving to a 26 shortly.

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I have been quite surprised how much gas I go through with my 86 Johnson 90 on my Montauk. I have two 12 gallon tanks. I have been averaging 16 gallons a trip - feels like a lot of gas for a "small" boat. I miss my four stroke Suzuki I had on my 19. Didn't use anywhere near this much gas and it was a larger boat.

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Seaworthy and fuel efficiency are two totally different concepts. Your boat is seaworthy, meaning it is in a fit condition and ready for a sea voyage. Your engine may not be fuel efficient and an older 2 stroke probably isn't very efficient. You should calc your fuel burn for how you run boat on average, that is number of miles per gallon based on the speed, distance and type of running you do. It sounds as if you either need to carry more fuel, so you can observe the rule of thirds or you need a more efficient engine. or you simply need to travel slower, and find the best speed to fuel burn ratio for you.

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Darren, it's not surprising that you used up lots of fuel running full throttle - I am surprised 12 gallons lasted anywhere near a full day. You'll probably find you get the best mileage at about 4000 RPM.

Tim