Fuel question

[BarrNone]

Just saw a gas station not too far from the house that sells reasonably priced ethanol free gas. Will this do any damage to a motor that has only had ethanol fuel in it? Thanks

 

[Offshoreman]

Nope. Not at all. The only thing it might hurt is your pocketbook. I imagine it's usually more expensive than the ethanol fuel.

What is the cost difference where you are?

 

[Dave LeGear]

Real gasoline has more BTU per gallon, so you "might" find you do not need as much throttle for same X RPM all other things being equal (sea state, weather, Etc.) when you switch over.

Now I did not notice is as much on the 2013 Yamaha F70. The 2004 Honda 150 I had though, one could actually feel a smooth throttle response and it spun up quicker on real gasoline. Some of this I am sure was from ECU programming and how it responded to sensor input from the lower quality fuel. The level of Octane in whatever it was running made a large difference for that engine and feed her 92 or 93 Octane and it always ran smoother

 

[BarrNone]

Honestly it wasn't that much more than the "regular" that they are selling. Running a Mercury 150 Verado and reading what others are hitting at WOT I just think I'm missing something as I'm getting around 10 mph slower than what others are hitting with the same setup. It's not that far from the house as I'd rather trailer it inland than pay on the water prices. Will it burn faster than normal?

 

[Dave LeGear]

Not really, just has more energy output per gallon than today's mixed fuels. As such, you might not burn as much to get the same output.

Octane is what you are looking to get for the higher the number, the more stable the fuel meaning... It will not explode before the Spark Plug fires it. Once that happens (uncontrolled knock and ping) the ECU starts backing off on the timing curve, and you will have to give it even more throttle for the same amount of work.

All things being equal though (including octane numbers on each fuel pump) don't see you getting another 10 mph faster just by changing fuel types. There are a lot of other things that come into play with your setup as compared to others, to make that comparison.

So let's start with the simple stuff 1st...

What is the WOT RPM on your boat when running in flat Sea States trimmed out?

When was the last time it was serviced manly Spark Plugs and Plug Wires?

Does she idle smooth or jump around a lot like she is dropping at cylinder?

 

[Offshoreman]

We should also consider outboard motor mounting height and prop: 3 or 4 blade, diameter and pitch.

 

[BarrNone]

If memory serves, WOT topped at 6200 RPM on dead flat seas at tide change. Plugs and wires changed at 200 hours, going to change them again before this season starts. She runs smooth at idle.

 

[BarrNone]

3 blade stainless at Mercury specs for the 150 Verado

 

[Offshoreman]

So the entire question would be:
What is your WOT RPM?
What is your WOT speed according to GPS?
What is the diameter and pitch of that prop?
What is the gear ratio of a rear lower unit?

there are a few more factors, but those are the fundamentals. Knowing that, we can do some calculations and see if maybe you're running to tall of the pitch, or potentially identifying another issue.

From my experience, it sounds like one or two pretty common issues. Either the pitch of the propeller is too tall, or the outboard is sitting too deep in the water.

There could be a number of other factors, but knowing the answers to the above questions would help me to help you identify why you're not achieving the performance you're looking for.

 

[BarrNone]

6200 WOT
35 MPH is the top speed I've seen on my Lowrance
Can't remember diameter and pitch right now
2.08 seems to be the gear ratio

 

[Offshoreman]

Next time you have the chance, take a look at your prop. It should have a stamping or a marking on it for diameter and pitch. We can figure out prop slip percentages and see where you are.

 

[BarrNone]

2 pics of my prop.

 

[Offshoreman]

If all of those numbers are correct, you have 17% prop slip at WOT. I think to start, you're under propped.

Is your hole shot snappy? I mean, it gets up and goes, gets on plane quickly?

I would suggest trying the next prop up. Same diameter, just the next pitch number up.

There are a lot of other factors that may or may not be affecting your performance. But with the numbers you've shared and that prop slip, I would try the next prop up to start.

 

[BarrNone]

She gets up on plane pretty quick. Which number is which?

 

[Offshoreman]

See how a 17 pitch prop performs. Probably bring your RPM's down about 200, your mid to top end speed will increase.