1970 Johnson 85HP Thermo Switch Function?

[68_Shark]

I am a newbie with a 1970 Johnson 85 HP on a 1968 Larson Tri-Hull. Got this rig about a month ago, it has some challenges. Engine had been run hot apparently due to bad impeller. Paint is peeled off the head from the heat. I had a pro do the impeller repair, but the engine still needs some TLC. The thermo-switch on the top of the motor, (see picture below) had the wires cut, I assume by previous owner. I got a new one and will install it, but what does it do? I assume it is an auto shut off, but would like to know for sure.

 

[racerone]

The switch on top of block has to with the choke.-------Most were disconnected.--------------------On a cold motor the choke would be partially on until the thermo switch opened

 

[68_Shark]

When you say ...Most were disconnected... can you elaborate. What was the reason that they were disconnected? Am I better off leaving it as is or putting in the new one?

 

[racerone]

Since most folks have trouble with using a choke it was an attempt to make the choke more " automatic "--------most were disconnected and dealers would educate owners on how to manually use the electric choke.

 

[F_R]

The motor has a two-stage choke solenoid. The thermo switch activates the first stage, partially choking the motor till it is warmed up enough to run w/o choking. The second stage slams the choke tightly shut for a cold start and is under the driver's control. Actually, BOTH stages need to be activated for a cold start.

All well and good, except sometimes under certain conditions, the thermo part would activate when it really wasn't necessary, causing some temporary rough running. For that reason, the factory came out with a service bulletin, telling the dealers to disable the thermo part and re-wire the motor so BOTH stages were under the driver's control. When he works the choke switch, both stages activate, when he releases the choke switch, it is wide open.

So, the question becomes---has it been properly re-wired? If it has, you don't need that new thermo switch you bought. If it is re-wired, BOTH choke solenoid wires will be going to the blue/white striped wire terminal on the board. In other words, three wires under that screw.

EDIT: Correction, wires are purple/white stripe, not blue/white

 

[68_Shark]

Thanks, I will inspect the wiring when I get home from work. I will be looking for three wires under the screw on the purple/white stripe terminal of the power pack. I hope I interpreted your response correctly, I am a newbie. Thanks very much!

 

[F_R]

NOT power pack. Nothing but choke wires under that screw.

 

[68_Shark]

Sorry, yes my incorrect terminology displays my newbie claim.

I should have said terminal block instead of power pack. There are three wires to the second terminal from the right, which is labeled purple/white on the back of the terminal block cover plate. Two of the wires lead to the same area of the choke mechanism, so I think it was properly re-wired.

The conclusion I come to is to NOT install the part that I purchased upon your advise, please correct me if I have misinterpreted your posts.

If this is correct; THANKS BIG Time.

 

[F_R]

You can revert it back to original by installing the switch. It won't harm anything, except you may experience the situation that prompted the change. I'd leave it like it is if it were mine.