Johnson 25 cutting out at full throttle

[ritchie]

I have a Johnson 25 (serial # 4450474) that sat up for about 8 yrs. I had a certified mechanic look at it this spring. He put new coils, plugs, points and condensor and checked it over. It ran great through the spring, then started cutting out on one cylinder. Changing the plugs seemed to work for about 3 weeks, then yesterday it began cutting out again at full throttle. I can cut back to 3/4 and it smooths out. Could it be the plugs aren't burning hot enough? They are gapped to .0030. I don't want to make too many changes before learning if the engine can handle other plugs.<br /><br />Any suggestions?

 

[fireman 757]

Re: Johnson 25 cutting out at full throttle

Sounds like you had another coil go bad. Run it Wot then shut it down and pull the plugs. Is one wet and fouled? Swap plug wires and do it again. If the other plug is wet black and fouled then it is that ignition coil.

 

[ritchie]

Re: Johnson 25 cutting out at full throttle

Thanks for the advice. I will swap the wires on the next trip. I'm not sure but it seems like the wires are only long enough to go to the specific plug and I'm not sure the timing would allow me to run the wire for the top plug directly to the bottom plug. If that doesn't work then I could take the coil assembly (including the wire) loose and swap the entire assembly. That should also help me isolate the problem. How does that sound.<br /><br />You think it is an issue of the coil (delivery of the spark) and not the spark plug? <br /><br />Thanks again for thinking about it.

 

[rolmops]

Re: Johnson 25 cutting out at full throttle

Hi.<br /> Swap the plugs but leave the wires with the cylinder they belong to,or both the plugs will look funny.If the same plug stays wet,You know it is the plug.If the other one gets wet,you know you have an electric problem.<br />Anyways it is better to eliminate the cheaper possibilities first,like run it in the dark and see if your wires are shorting out,or check your points and condensers.Sometimes a loose wire is the culprit. These are things you can do by yourself.

 

[iRich]

Re: Johnson 25 cutting out at full throttle

You're right...you need to swap the coil not just the wire from it...<br /><br />Rich

 

[ritchie]

Re: Johnson 25 cutting out at full throttle

Thanks guys. On my last investigation, before I changed the plugs, I thought I noticed one plug was running hotter than the other and a difference in the look, smell and feel of one of the plugs. Maybe its just a coil. Think I'll buy an extra anyway. <br /><br />The 'run it at night to look for a short' was a really good idea. Would be nice to fix it with a piece of electrical tape!!!!