1972 Johnson 100hp ran through sand, lost power

[Jfg92]

I have a 1972 Johnson 100hp outboard on a 1974 16’ StarCraft. We recently ran it in the shallows (in the sand) for a short period before getting out and pushing it into deeper water. After this episode, the boat is only running at about 60% power. Once we noticed the diminished power we got towed back to shore and haven’t used it since. We figured it was the water pump / impeller so we changed that out; however the old one still looked great. We were thinking we may have overheated however we had heat issues in the past and the hot horn always came on (we checked, the hot horn still works). We haven’t brought the boat back on the water yet to test it. Any other ideas on what could’ve happened to cause the diminished power issue?

 

[interalian]

Maybe you got it hot enough to damage a coil and you're down a cylinder. Do a drop test. Probably a good idea to do a compression test too.

 

[racerone]

Motor is running.-----Motor only has one ignition coil.----Run at night and look for sparks leaking out.-----Remove flywheel.----Remove distributor cap / rotor.----Inspect anti-reversing spring.-----Clean cap and rotor.----Possibly replace wee boots on plug wires.----Note ,---wires screw into the cap.

 

[F_R]

Repeated overheatings, eh? Compression test first, to make sure you have something left to fix. Then an orderly trouble shooting is in order. Guessing and assuming does nothing but empty your wallet.

 

[racerone]

Agreed-----Check for loose head bolts as that is an indication of repeat overheating.----And of course the all telling compression test.

 

[jimmbo]

We were thinking we may have overheated however we had heat issues in the past and the hot horn always came on (we checked, the hot horn still works).

Well the horn worked, that doesn't test the thermal switch.

As mentioned before, Compression test first.

 

[oldboat1]

Likely have to flush it out before use again, if you haven't done that. Pull off the l.u. and run some water up the tubes. Good idea to do a t.stat/vernatherm check. Flush out, and check for open bypass.