"Geoff" wrote in message
news:381219_304c08e7ace62127a9d6abb97696a250@boati ngforumz.com...
I have a sea ray with 4.3 mercruiser, the boat was running fine all
season until 2 weeks ago. It will run fine if you keep it around 2,000
rpms but then when you start to go faster, it will surge from 3,000
rpms to 4,000 and continue to do that until it stalls out. Its not the
prop, the prop was changed at the beginning of the season and is still
in good shape. Its also not water in the fuel because the fuel tank
has been drain and fuel and water separator filter has been changed.
I'm really lost on this one.

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Sounds to me like the fuel supply is having trouble keeping up. As the
mixture goes leaner it can cause surging. I'd check along those lines
first. Some of the fuel tank pickups have a screen over them. Some carbs
have a smaller inlet filter just under the fitting where the fuel line
enters. I have seen also water/trash gum up the flappers that act as valves
in the fuel pump.