[Destroyer]

First things first. If I recall, a 150 hp 1500 is a Merc "Tower of Power" inline 6 cylinder. (L6) It has no detachable head. Everything was bored from the crankshaft side of the engine at the factory. The V6 for the same year was rated at 155 HP

I still have a L6 115 hp 1150 Engine. Sold my L6 90hp when I sold my Cruisers Inc. boat. Actually they are good engines, just a pain in the *** to work on if you need to go "inside" the block.

You should be able to get the engine to rev well over 5 grand under load in the water. The book says NEVER go over 1000 RPM on land with muffs.

You say the engine will scream and run all day @2500. By scream I take it you mean well over 3500 and you're in the water, just without the prop engaged? If that's the case then it sounds like you might have a drivetrain problem. Have you checked behind the prop for rope or fishing line wrapped around the shaft? With the engine turned off does the prop rotate freely when not in gear? With the spark plug wires off (label them) and the plugs removed can you freely rotate the engine flywheel by hand with the lower unit engaged? If not then you may have a problem with your gears or your gearcage or your driveshaft. Did you check/change your lower unit lube? Oh, and what size prop and pitch are you using?

Some specs on your motor: It's an L6, 150 hp, 4800-5800 RPM @ WOT, Spark plug is a Champion L76V, Primary Pickup is 4-6 Degrees BTDC, Max timing is 21Degrees BTDC, no points, Type "A" carbs (Side bowl and back drag type), "Thunderbolt" distributor with pointless CD ignition and your firing order is 1-4-5-2-3-6. The L76V spark plug has a set gap, no adjustment is required. (The NGK BU8H gapless spark plug will also work and is the recommended plug for all V6 powerheads after 1987)

If you need any other specs let me know and I'll look them up for you.