Fuel Usage

[supreme]

Hello, I am a newbie to the power boating world. I have 16 ft alum. side console with a 40 hp Evinrude 74. I had it out for the first time on Sunday my daughter age of 10 and I, combine weight 225, for about 1 1/2 hour a little cruising 5 mph zone and a little WOT, it run pretty good. I burned about six gallons, is that about right? It sounds like a lot to me. The prop is 10 1/2 13 and the motor wasn't trim out at all. Is this what to be expected in fuel usage?

Many thanks for all the info: in the forum.

 

[NelsonQ]

Re: Fuel Usage

First of all, welcome to the forums supreme.

Good rule of thumb is 10% of horsepower is your hourly fuel consumption at WOT. So 40HP, would be 4 gallons at WOT for 1 hour.

With 1.5 hours on the water, a 'little WOT' (don't know how long a little was) and without the motor trimmed, you're pretty close.

I'm not to guy to comment on prop, but it could also have an affect on this as well.

Hope this helps. For reference, I had similar consumption in a '65 Merc 50 HP and it was on a 14' runabout so you're pretty close. (My 115 now eats that in 30 mins at WOT)

 

[Splat]

Re: Fuel Usage

Sounds like it may be a little bit much. Typically most of us use a formula like putting a decimal point one space over from the left number of the hp. This will give you a rough guess of fuel consumption per hour.

so a 115hp will burn like 11.5 g/hr.

or in your case 40*.10=4.0 gph

4*1.5 hours= 6 gallons total

Still seems a little high to me if your just putting around.

Bill

 

[Splat]

Re: Fuel Usage

looks like supreme and I were typing at the same time.

and he's a little quicker.

BIll

 

[supreme]

Re: Fuel Usage

Many thanks guys, I am going to rebuild the carb. to see if that will help a little.

 

[QC]

Re: Fuel Usage

It sounds like a lot to me. The prop is 10 1/2 13 and the motor wasn't trim out at all.

Why no trim? Did she get up on plane easily enough? Was the bow "plowing" at all? Fuel use does sound a little high, but this is a 35 year old two stroke . . .

 

[supreme]

Re: Fuel Usage

Just got back from work. The thrust rod or pin is missing so I couldn't trim the motor. I just picked one up I'll try it out tomorrow, I hope! It did get up and plane, but it did feel like it was working on the low end cruising. Theres four holes any suggestions were I should start. It's a light alum. boat 16' Lunker alumacraft. Thanks for the help guys.

 

[DJ]

Re: Fuel Usage

Start at one out and go from there. You'll have to experiment a bit.

The highest you can go, without cavitation, is where you want it.

 

[Boatist]

Re: Fuel Usage

I would also suggest do not run WOT if you want fuel mileage. My 140 hp on a 21 foot Aluminum Runabout will run 3 hours plus and cover 70 miles in the ocean on 15 gallons of fuel but I do not run WOT very often.

 

[tashasdaddy]

Re: Fuel Usage

those motors have what was called "cruise control" they were built to start at wide open throttle, the feather back to 7/8 - 3/4 throttle, this kept the timing advanced, and feathered the carbs to cut fuel consumption. you will only notice 1-2 mph drop in speed, but can be significant drop in fuel usage. works on the new motors also. but if you run to 3/4 throttle, and don't go to wot, you will use more fuel, just the way they were set up.

 

[haskindm]

Re: Fuel Usage

That may be a little on the high side for consumption, but remember that it is a 35 year old motor and motors from that era were not known for their fuel economy. My advice is: If the motor is running well otherwise (idles smoothly and no excessive smoke) LEAVE THE CARBS ALONE! They are tricky things, and if it ain't broke - don't "fix" it. If there are other signs that the carbs have problems - leaking fuel, smoke when engine is warmed up, rough idle, hard to start, etc. - that is a different story, but to rebuild the carbs in an attempt to improve economy would be a mistake. You will need a tachometer to determine if your prop is correct. The correct prop will allow the engine to reach it's recommended top RPM at WOT with the boat typically loaded. You do not want the engine to be lugging and running at a lower than recommended RPM at WOT and at the same time you do not want the engine to run at a higher RPM than that for which it was designed. Don't guess, hook up a tach at least temporarily and make sure that it is right.