please help im going crazy

I have a 1983 mercruiser with a 260hp moter sitting in the yard on a hosr it runs and sounds perfect when I put it in the water and try to take off it dont want to get up on plane if there is somebody in the back I put a brand new 4 barrel carburetor on it yeasterday I can get all the way up front and it will plane out and run fine and then it gets hot and dont want to crank back replaced the coil yeasterday also got 7500 in boat please somebody tell me whats wrong could it be the prop its got a 19pitch on it now please let me know

Compression is what on a warm engine, all the spark plugs out and the throttle fully down?

Keep track of what plug came out of what hole.

Post back we will go from there.

You'll need to determine whether or not the prop diameter and/or prop pitch is correct, and if the final drive ratio is correct for this engine.
This involves a WOT RPM test (wide open throttle rpm).

In order to perform a WOT RPM test, the engine must be in full tune and must be healthy.
This will include ignition timing.... and more specifically the progressive and total advance at the correct RPM for Marine use.

See your OEM specs for this info.



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I can get all the way up front and it will plane out and run fine and then it gets hot and dont want to crank back

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When was the impeller last replaced? A 1983 boat...the hull, floor, stringers and floatation foam may be waterlogged.

You have a 30 year old engine with no assessment on its mechanical "health" (other than it "sounds perfect") ...what do you expect it to do??? I'd start with the compression test before putting any more money into it...

makomark said:

You have a 30 year old engine with no assessment on its mechanical "health" (other than it "sounds perfect") ...what do you expect it to do??? I'd start with the compression test before putting any more money into it...

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Ayuh,... Agreed,...