OLD Johnson 40HP. Only one cylinder running?

[robmurray]

I have an old Johnson 40hp (estimate late 60's model) - its the motor on the cover of the Clymer manual for old Johnsons. <br /><br />Currently only one cylinder is running. Checked the cylinder, the piston is moving, checked the spark, only getting a VERY small spark from the plug, but getting a strong spark from the other plug in the cylinder which is working great.<br /><br />Any ideas? I had thought that even a weak spark would be enough to ignite the fuel mix? Plugs are brand new, and the leads are fine Im sure, never had a problem with them before.<br /><br />Thanks

 

[bhalsdorf]

Re: OLD Johnson 40HP. Only one cylinder running?

Sounds like you have a bad coil. They are still available.You will need to pull the flywheel to change it.

 

[OBJ]

Re: OLD Johnson 40HP. Only one cylinder running?

Hi Rob..<br /><br />What Bill H said and a little more.<br /><br />While yer under the hood, take a look at the points and condensers. Points that have been used for a while will also cause the same problem. If you don't know how the last time they wer changed out, it would be a good idea to change them out. Also look at the condition of the spark plug wires and any wiring under the flywheel. The wire insulation on the older motors have a tendency to dry out and crack. Keep us posted.

 

[dkondelik]

Re: OLD Johnson 40HP. Only one cylinder running?

As long as you've got the flywheel off, you might want to clean or replace the points on the weak side first. If a bug left some stuff on the contacts, it could be contributing to the problem.<br /><br />Points, Condencers & Coils can usually be found at your local omc dealer or Napa.<br /><br />If the "good" coil is cracked (seems to happen with age on some of the old ones), you'll probably want to attend to it at the same time.<br /><br />I think you'll find that 1/4"x20 is the thread to use on the flywheel (when you use a gear or flywheel puller to remove flywheel).<br /><br />Good Luck<br />HAVE FUN!

 

[JB]

Re: OLD Johnson 40HP. Only one cylinder running?

Hi, Rob.<br /><br />We need a model number. Estimates of engine year are often way off, and there are big differences between 60s and 70s OMC 40s.

 

[OBJ]

Re: OLD Johnson 40HP. Only one cylinder running?

AAhhhh JB....once again your widsom is only overshadowed by your good looks...

 

[robmurray]

Re: OLD Johnson 40HP. Only one cylinder running?

Many thanks to all, I will do that. I will try to get the model number but I have been having a few problems with the model number to date.