Johnson GT 150

[mikeroe]

This is my first time on here and I have been thru all threads I can find on my motor. I am also new to boating. I have recently bought a '89 Tracker fish and ski boat. It had been upgraded with a '90 Johnson GT 150. I have read on here that it's a good idea to verify that it's actually a GT 150 and not just a 150 with a GT cowling. I checked for the model and serial number but the nomenclature tag on the middle section is missing. Missing may not be the right word since I don't see where it would have been. I also read here to check the top of the head on the port side of the motor. The disk that looks like a freeze plug has only one number stamped on it....R8247810. It also has an M stamped above it that looks sort of like the proof marks you see on fine silver. Also, on the front of the lower unit is an add on water pick-up. At least this is what the seller told me it was. The motor runs great. A lot faster than I'm comfortable with at this time in my boating experience. My question is, what do I have? I would appreciate any help I can get.....Mike

 

[emdsapmgr]

Re: Johnson GT 150

Not all the crossflows had serial/model numbers on the casting plug on the top of the block. The factory also stamps that information on a tag and puts it near the swivel bracket, just below the powerhead. You are looking for a special model code with an "S" added. For instance, the model code on a GT/XP 150 will always read 150S. It's the S which adds performance items to the engine: vented cowling, optional cowling badging, usually performance heads and 175-type carbs. Many of these engines also came with the high output 35 amp alternator, with the vented flywheel. Put out close to 165 hp. You can also look on the top of the block itself. There is a stamping in the casting. It will show the model number-likely painted over. See attached picture. This pic shows the stamping 150S, and a date code, perhaps 6/13/85.

 

[mikeroe]

Re: Johnson GT 150

I appreciate your help. The only other numbers I have found so far are the casting numbers on the heads...332544, and 332545 D2. I will go back out and look if and when the rain stops

 

[mikeroe]

Re: Johnson GT 150

I do have another question about is motor. Since I have no plans to run this WOT in the foreseeable future, I was told I might want to back off the amount of oil I mix in the fuel. This boat doesn't have VRO. I'm real hesitant about fooling around with this without any expert opinions.

 

[emdsapmgr]

Re: Johnson GT 150

Those heads first came out on the 1986 GT models. The heads exclusive to that GT model. (The base 150 engines had other heads.) Used up through the 89 XP/GT's for sure. That's good news. I'd also pull the airbox off the carbs. The carb face flange should have the size of the carb throats cast into it. They should be 1 5/16- the size (in inches) of the carb throats. Those were the 175 carb size. If that checks out, likely it's the GT/XP version.

 

[mikeroe]

Re: Johnson GT 150

Yes that is good news. I will double check the carbs tomorrow. I just hope this isn't more motor than I'm ready for at this point. I don't want to sound wimpy but inexperience and too much power can be a dangerous combination. Thanks for your help.

 

[emdsapmgr]

Re: Johnson GT 150

A GT/XP 150 engine will actually put out close to 165 hp.