1973 merc model 110 ignition issues

[ArrowNaughtic]

My '73 Mecury model 110 9.8 hp serial number 361558 is losing the top cylinder after about 5 - 10 minutes of trolling. After talking to a buddy of mine he thought I should not be using the new spark plugs I had just installed. They were NGK gapless style.
I went to the NAPA store and purchased 2 NGK electrode style plugs and gapped them both to .022 and tested those out in my tank. After 10 minutes of running at a slow idle the top cylinder went out again and even revving the motor up in neutral did not bring it back like it had on the gapless style plugs. The guy at the marina told me he thought it was a bad or weak coil. Is there a way to test the coil to see if it loses power after the motor is warmed up?
Or should i not be so focused on the coil issue and be looking at something else?

 

[merc850]

Re: 1973 merc model 110 ignition issues

That motor uses Perma Gap plugs (probably a decal on the powerhead says) so put the gapless ones back in. When you run the motor and the top cyl. dies pull the plug out and ground it to the block where you can see it. Spin motor over and see if it sparks a strong spark (you should be able to hear it too!).

 

[ArrowNaughtic]

Re: 1973 merc model 110 ignition issues

Ok, will set up the tank again and check the spark........ So those definately do call for the gapless plugs. Thanks for the info, funny that I have that decal and it NEVER registered with me. (slaps forehead.....doh!)

 

[ArrowNaughtic]

Re: 1973 merc model 110 ignition issues

Update on this issue.......... Turns out I had a loose coil wire in the top cylinder. Pulled it out of the coil and cleaned up the connections and reinserted it. Both cylinders fire beautifully and it has been running very sweet. Still need to adjust the idle on the carb, I boat in a couple of different elevations (sea level and at 3,000ft) so may have to adjust depending on where i am trolling at. Problem solved! Thank you for the help.