1991 Johnson GT 150 Seized?

AB Boater

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Jul 23, 2023
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Hi all, new to the forums here, and hoping for some help. I’ve scanned through similar topics, but can’t find someone with the same issue I’m facing. This post will be long winded as I try to give as much detail as possible.

I just bought a 1992 Searay 180 with a 1991 Johnson GT150 on the back (JV150SLEIE to be exact). When I originally looked at the boat, the owner ran the boat on muffs in the driveway. It fired right up and idled smooth. When I came back to pick the boat up, he revealed that the boat has been out of the water for 2 years, but he removed “most of the bad gas”. When I got it home, I filled the rest of the tank with premium and gave it a heavy dose of SeaFoam.

First trip to the lake wasn’t the greatest. It would stall at idle and low speeds, so trailering was fun. Seemed to run great at anything above idle. No hesitation and ran smooth, but would still stall out pretty quick when I brought back down to idle. During this trip I found out the tach wasn’t working. Following advice I found in this forum, I grabbed a new tach, which also didn’t work. So I jumped my grey wire to yellow/grey at the engine terminal strip and it started working. I am waiting on the new rectifier to come in.

I took it out a second time to see if the SeaFoam and new gas had any effect, but the boat was running about the same.

After my second run, I looked up some manuals and started to tear things apart. I changed spark plugs to OEM recommended Champion plugs, changed fuel filter and ran a Johnson/Evinrude decarb spray. One thing worth noting is that during the decarb, the SLOW alarm came on as the bucket of water had dropped below the water intake. I quickly jumped out and added cold water, and the engine was running at idle during the time, so I don’t think this caused any damage.

My third and final trip, things seemed to be going great. Idle was much smoother, still not prefect, but it was good enough to trailer and dock before stalling. My top end was also about 5MPH higher. About half hour into our trip running at WOT at the time, there was a loud thud and I lost all power. Engine was still revving high, felt like a spun prop. I immediately dialed the throttle back to idle and cut the engine when we came to a stop. I started it up again after a quick inspection and it was running rough, almost felt like a misfire. So I started back very slowly to the marina. Ran for about 5 minutes then died. After that, starter would only make a clunk and stop. Pulled the cowling and saw the flywheel seemed to be stuck, tried pull starting and couldn’t get the flywheel to move an inch.

From scanning all the forums, I read to take plugs out the plugs and try to turn the flywheel, as the compression may be preventing me from turning. Pulled all the plugs and no luck. Also, I didn’t notice any water in the cylinders when I pulled the plugs. I have yet to pull the leg to isolate the issue to above or below yet. That’s my next step.

I’m no marine mechanic, but in my limited knowledge, a seized engine would either be a lack of oil or water in the cylinders. Either of which would cause heat and the SLOW to activate, which I know was working. I’m stumped, and trying to avoid spending thousands at a marine mechanic on a 30+ YO engine. Any help or pointers would be greatly appreciated!!!
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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50,874
Did you add 2-stroke oil to the tank?
 

AB Boater

Recruit
Joined
Jul 23, 2023
Messages
3
Yes I did. I can confirm the pump was working as there was some 2 stroke oil in the air box and the tank level had dropped from when I filled it (no leak and oil tank primer is super tight).
 

brodmann

Chief Petty Officer
Joined
Jun 17, 2008
Messages
426
You said after you lost all power, the motor was still running. After that the motor started up again. I'd drop the foot and see what difference that makes. I would put the control in neutral and see if you can spin the prop freely. My son had a 90 HP Johnson that started running very sluggish and was guzzling fuel. When he had this problem and checked coils, plugs and rebuilt carbs with no improvement, I was at his house and discussing the problem with him while leaning against the back of his boat. I kicked the prop lightly with my foot and it didn't move! We discovered that his lower unit had bad seals, had been filling up with water and was almost completely locked up! I'm guessing that if we had not discovered that problem and he continued to run the boat, the foot would have eventually locked up. So, put in neutral and see if the prop spins freely. If not, drain the food and see if water or nothing at all comes out. Lower units are much easier to replace than powerheads!!! You'd probably have no problem finding a foot for that motor by looking for a non-running motor.
 

AB Boater

Recruit
Joined
Jul 23, 2023
Messages
3
You said after you lost all power, the motor was still running. After that the motor started up again. I'd drop the foot and see what difference that makes. I would put the control in neutral and see if you can spin the prop freely. My son had a 90 HP Johnson that started running very sluggish and was guzzling fuel. When he had this problem and checked coils, plugs and rebuilt carbs with no improvement, I was at his house and discussing the problem with him while leaning against the back of his boat. I kicked the prop lightly with my foot and it didn't move! We discovered that his lower unit had bad seals, had been filling up with water and was almost completely locked up! I'm guessing that if we had not discovered that problem and he continued to run the boat, the foot would have eventually locked up. So, put in neutral and see if the prop spins freely. If not, drain the food and see if water or nothing at all comes out. Lower units are much easier to replace than powerheads!!! You'd probably have no problem finding a foot for that motor by looking for a non-running motor.
The prop spins freely in neutral. Nevertheless, I will definitely remove that leg as I also hope that where the problem lies!
 
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