Quote:
Originally Posted by Smith Point
Thanks guys,
I think you are right. I need a pro to check it out. I'm convinced that its a carborator problem, the boat came with a 14-12 prop, higher RPM but tough getting out of the hole, switched to a 14-14 prop the boat popped out of the water, now i have a 14-13 prop good compromise. The hull is clean, and it runs great so i don't think its the plugs. Just terrible fule economy. Is there a website that i can double check RPM vs. MPH?
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Not likely any website that has data for your boat. What is the gear ratio of your transmission? With that info we can easily calculate the prop slip for given speeds and RPMs.
My request for spark plug info was specifically to check the carburetor, not the plugs themselves.
Here's chart of speed vs MPG for a Malibu Response ski boat. Note how precipitously the MPG drops as the speed goes above 27 MPH. It drops from 4.3 at cruise to 1.75 MPG at WOT. That's like your boat and typical for a ski boat.
Here's a chart for a similarly sized stern drive boat. Note how the MPG does not drop nearly as badly once it's on plane. The MPG goes from 4.2 at cruise to 3.4 at WOT. That percentage of fuel use difference is pretty typical for a stern drive boat.
Note that both boats cruise at 25-30 MPH with very similar fuel burn, and they both top out at 50 MPH, but the ski boat requires about twice the HP to hit 50 because the prop thrust cannot be vectored with trim.
My advice would be to keep it below 30 MPH and above 20 MPH when possible.