Gas on surface of water around engine

[fishing dad 2011]

Hi... Was just wondering if anyone might have an idea of what might be causing the fuel ring around my engine (outboard) when its in the water. I dont see any apparent leaks in the fuel lines etc. could this be coming out of my exhaust??? Possibly over fueling???? It does seem to use alot of gas but it runs great and I am afraid to mess with it because the old saying "if it aint broke dont fix it"... Any Ideas???

Its a evinrude 70 hp. 1979 thats in great shape I will try and attach a photo

 

[Will Bark]

Re: Gas on surface of water around engine

If you are talking about the boat just sitting still after running it is most likely unburned fuel coming out of your exhaust which is normal.

 

[Bigkat650]

Re: Gas on surface of water around engine

If you are talking about the boat just sitting still after running it is most likely unburned fuel coming out of your exhaust which is normal.

x2 it doesn't take much gas at all on the surface of the water to be able to notice it. I would think unless it is a real abundant amount--then you don't have much to worry about.

As far as gas consumption, what kind of boat are you pushing and how much gas are you burning up in an outing?

 

[fishing dad 2011]

Re: Gas on surface of water around engine

15'6" starcraft trihull using about 6 gal - 10 gal an outing(4-6 hrs.)

 

[Bigkat650]

Re: Gas on surface of water around engine

I have read there is a formula to determine how much gas your motor should be using at WOT. I believe the rough estimate is a properly tuned 2-stroke motor burns between .6-.8lbs of fuel at WOT per HP per hour. Gas weighs about 6.02lbs per gallon. If we figure on the high end, that your motor will burn say .75lbs per hp per hour--it will burn 56.25 lbs of gas every hour. Divide that by 6.02, and that's 9.34 gallons of gas per hour of use at WOT. If your boat goes 35mph at WOT, this would mean your boat gets roughly 3.75 miles per gallon of gas at WOT. The one thing I don't like about this formula is it does not take into account engine RPM at max throttle. Does that affect things? I don't know for sure, but I assume it would.

So is 6-10 gallons of gas in a 4-6hour trip bad? Well it really depends on how much your using your motor, and how hard your pushing it. Most people operate their boat/motor at what is known as 'cruising speed', which usually is somewhere in the realm of 75% of WOT, where is where you get your best gas mileage. (assuming your boat will be on plane at 3/4 throttle that is)


This is what I've researched--granted they say you cannot believe everything you read online, which is where I found this info, so the whole formula may be completely worthless. Anyone else ever use this formula? Is it even mildly accurate? According to the article, I believe 4-strokes burned closer to .5lbs per hour per HP at WOT if anyone was interested.

 

[tx1961whaler]

Re: Gas on surface of water around engine

Too complicated.
A rule of thumb is 10% of the HP rating in gallons per hour at WOT.
So a 70hp would burn about 7 gph at WOT. A 100hp would burn roughly 10gph at WOT.

 

[emdsapmgr]

Re: Gas on surface of water around engine

Make sure the airbox drain hose is connected to the hose barb on the block. If it leaks, it will drip fuel down the cowling into the lake. Also be sure the airbox gasket is in place between the two airbox covers.

 

[fishing dad 2011]

Re: Gas on surface of water around engine

Thanks guys... I will check that airbox thing and the drain tube..