1972 Johnson 20 hp

[amvaneyk]

I bought this motor from a guy that had it sitting in his garage. It has an electric start. The carb has been rebuilt, points look good, got a great spark in both plugs, new fuel pump. When I start it, what happens is when it hits it makes a loud backfire noise. Can anyone help????

 

[samo_ott]

Re: 1972 Johnson 20 hp

As a baseline you should do a compression check.

After it backfires, does it start? Run? Or die? Are the plug wires on correct? The one with the metal clip should be on top.

Oh, and welcome to the forum.

 

[JB]

Re: 1972 Johnson 20 hp

Howdy, Vaneyk.

Welcome to iboats.

Sounds like the spark plug wires are reversed. Switch them and let us know what happens.

Good luck.

 

[samo_ott]

Re: 1972 Johnson 20 hp

Phew... Glad I got my response in there first!

 

[tashasdaddy]

Re: 1972 Johnson 20 hp

also, if you did not torque the flywheel nut, when inspecting, the woodruff Key between the shaft and flywheel will shear off, and throw timing off. causing the same problem.

 

[amvaneyk]

Re: 1972 Johnson 20 hp

Yes, compression is good. The spark plug wires are right. I didn't torque the fly wheel I may have to check that out. After it back fires it doesn't run.

 

[tashasdaddy]

Re: 1972 Johnson 20 hp

bet you find a shear key. BRP part 0120395 KEY, Crankshaft. DO NOT USE A HARDWARE STORE KEY.

 

[amvaneyk]

Re: 1972 Johnson 20 hp

I will take a look at that tonight guys. Thanks alot for the quick help!

 

[amvaneyk]

Re: 1972 Johnson 20 hp

Does anyone know the torque specs on that fly wheel nut?