My '61 Lark 3 has a serious drinking problem..

[LxAV]

Well, now that my '61 Evinrude Lark 3 40HP has survived its hangover from the diesel cocktail I Gave it last week, I have another fuel related question:
It consumes a lot of fuel. I mean really a LOT.
On an average boating day, cruising through the canals of Amsterdam at 7km/h for about 4 hours, it drinks about 20-30 liters. I can't believe that's normal.
I'm thinking about replacing the piston rings, because I came up with the idea that worn out rings might spill fuel during compression ,thus causing the engine to consume way more fuel..
Does that make sense or am I on the wrong track?
Could replacing the rings drastically reduce my fuel costs or are these old engines simply 'build to spill'?

Comments, ideas and experience are highly appreciated!
Thanks, Alex

[redtech]

if compression is ok 70-90psi then look elsewear.
if you have a tach find out what your max rpm is if it's in the rpm range just having tomuch prop can use a lot of fuel

[LxAV]

I don't have the tool to measure the psi but turning the axxis by hand is quite heavy and a huge difference when I take out one or both sparkplugs, I'm guessing (but true, just a guess) the pressure is ok.

I can check out the rpm rate from the manual and I'm looking to build a rpm meter for the dashboard so this I can check, but what exactly do you mean by 'to much prop' ? You kinda lost me there..

cheers,
Alex

[redtech]

when pitting boats together or rigging them the last step before delivery is to test drive the boat and prop it. the test drive means everything the rigger did is ok the propping is to mach the boat with the right prop pitch. if the rpm range is between 5000-6000rpm the you drive the boat and find out the your turning 4800rpm this means you have to much pitch so say we go from a 21p to a 19p this will give you better holeshot, higher top end rpm, better fuel economy,and longer engine life.

[LxAV]

You almost lost me there, but I googled 'prop pitch' and it's all clear to me now.
I read this page and it's very helpfull:
http://www.caravelleboats.com/propeller%20info.htm

My prop was on the boat when I bought it, I have no reason to believe it did not come with the engine as a stock prop.

As soon as I get hold of a desent rpm meter I will look into this and if nescesary consider buying a better suited prop.

Thanks for the tip!

Alex