1980 150 hp Johnson motor died and will not start

[sundrop]

I bought a 1980 150 hp Johnson for my bass boat in March of last year. Ran good all season. On my 3rd or 4th trip out this year I began to have trouble. Boat would not plane off for about 3-5 minutes but would eventually plane off...took longer to plane off each time out. When I would try to restart the motor a second time while on the water, it became hard to start.

Last time out, it was hard to start, even the first attempt was now difficult. Did get it started, though, and ran smoothly for about ten minutes. All of a sudden the mph dropped from about 45 to 30. Ran that way for about two minues into the docking area, but when I de-throttled it cut off. Motor will not start. Good charge on battery...even jumped it with another good battery. Rebuilt the starter last week. Water pump is pumping. Now the motor barely turns (like an inch or two) when I try to start it. I'm getting 12.6 volts all the way to the starter. I'm afraid the motor is locked up.

I have a very limited knowledge of boat motors. When all of this first started it SEEMED that something was draining the battery, so I disconnected the terminals and checked the stator and rectifier...both check out good.
I'm stumped...any help out there would be greatly appreciated

 

[ab1]

Re: 1980 150 hp Johnson motor died and will not start

Check compression first and then let us know results.

 

[emdsapmgr]

Re: 1980 150 hp Johnson motor died and will not start

When you have the spark plugs out for the compression test, shine a pencil light in each plug hole and see if you can see anything, such as scuffing on the cylinder walls.

 

[sundrop]

Re: 1980 150 hp Johnson motor died and will not start

Thanks for the suggestions. I will be able to search it out further the end of next week.

 

[sundrop]

Re: 1980 150 hp Johnson motor died and will not start

compression is 65, 65 ,65 on port side; 80, 80 65 on starboard side.

 

[emdsapmgr]

Re: 1980 150 hp Johnson motor died and will not start

You should be looking for at least 90/95 lbs compression. That powerhead has some serious issues base on your compression numbers. You should run some Bombardier Engine Tuner through the engine and see if you can get the compression numbers to come up. You may need to pull the heads and check the head gaskets.

 

[kenmyfam]

Re: 1980 150 hp Johnson motor died and will not start

If the compression gauge is fairly accurate then those numbers are low and too far apart.
Can you turn the flywheel easily by hand with the plugs out ???