need help from someone with old merc experance

lathehand · #1 06-24-2010, 05:38 PM

I have a 1977 150 hp merc1500 that won't rev up over 2500rpm.I've tried everything from rebulding the fuel pump and carbs changed all fuel lines and water seperator .Done new plugs wires and cap rechecked the link and sync and still ng.I'm not very good with timeing and carb sync.Out of gear it'll scream and it will run all day at 2500 rpm.One more thing I checked the compression and found all 6 cylinders are within 12 lbs of each other.What have I overlooked

macojoe · #2 06-24-2010, 08:57 PM

Its a Merc!!

J/K the motor heads will be by soon!

Destroyer · #3 06-24-2010, 09:51 PM

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.

lathehand · #4 06-25-2010, 06:12 AM

destroyer your right on about the heads.It's just a water jacket.When I said it'll scream Yes out of gear but in the water.The prop spins freely by hand and the prop size ie 13and3/4x17.I've tryed to rase the trim up it don't seem to make much differance.I't almost seems to me to I'm not gettin the high seepd circut between the carbs and distributor

spareparts · #5 06-26-2010, 08:41 AM

is it the modelwith a distributor, or does it have switch boxes? Sounds like the high speed windings are gone in the stator

spareparts · #6 06-26-2010, 08:43 AM

http://www.cdielectronics.com/

Destroyer · #7 06-26-2010, 12:05 PM

Quote:

Originally Posted by spareparts

is it the modelwith a distributor, or does it have switch boxes? Sounds like the high speed windings are gone in the stator

Check the specs in my first post on this thread. Those specs are for a 1977 L6 inline 6 cylinder engine (1500) He has a distributor, but no points. (CD ignition) The fact he said it will scream when not in gear kinda points to the high speed windings working.... Certainly worth looking at though.