Dale in MD
Cadet
- Joined
- Jul 15, 2010
- Messages
- 12
After 2 weeks of frustration, I finally got my problem fixed and wanted to share it here in hopes of helping someone else.
Issue - I kept losing a cylinder at lower rpm's which eventually would escalate until I couldn't keep 2 cylinders firing even at WOT. Pulling plug wires one at a time would just result in a swap of the "running" cylinder.
I had replaced plugs (UL81C's), replaced wires, replaced condensors, gapped points and ensured they did not have high resistance, checked driver and external coil resistances, and checked for grounds and breaks in wires everywhere. Ensured kill switch wasn't cause. Yet despite this stuff (about 5 different times!!!!) , I could not get my engine to run on both cylinders consistantly and sometimes, I couldn't even get spark on either. I probably had 10 solid hours of searching the web (mostly this site) for answers. One thing I came across a handful of times was the the 1974-1976 Johnson 9.9 /15 HP engines just didn't do well with the Champion UL81C spark plugs. People found that engines that ran horrible, or not at all, on the UL81C's would run just fine on the NGK B7HS plugs. Being at the end of my rope with this thing, I figured it was worth a try. I hate to put plugs in a motor that are not called for by the manufacture, but all the stories I read matched mine to a T. I did a few checks to ensure that the NGK B7HS was as "equivalent" to the UL81C as possible and then went a got a set. She started right up and ran flawlessly when I went for a test ride.
Something obviously changed on my motor to have made the UL81C's perform badly (even a brand new set) because they had ran fine in the motor previously. However, whatever changed was very subtle and is not something that will show up through normal component checks. I may have been able to replace all 3 coils, both points, both condensors, and my wiring harness, and been able to run the UL81C's again, but its tough to throw that kind of money into an old motor - and then HOPE it fixes it.
And the best part is........ the NGK's cost half as much as the Champions where I bought them! For this particular make, model, and year of motor, the NGK plug seems to be the ticket. I was skeptical about the other peoples claims of how the plug swap solved all their issues, but now I've seen it with my own eyes.
Hope this helps someone.
Dale
Issue - I kept losing a cylinder at lower rpm's which eventually would escalate until I couldn't keep 2 cylinders firing even at WOT. Pulling plug wires one at a time would just result in a swap of the "running" cylinder.
I had replaced plugs (UL81C's), replaced wires, replaced condensors, gapped points and ensured they did not have high resistance, checked driver and external coil resistances, and checked for grounds and breaks in wires everywhere. Ensured kill switch wasn't cause. Yet despite this stuff (about 5 different times!!!!) , I could not get my engine to run on both cylinders consistantly and sometimes, I couldn't even get spark on either. I probably had 10 solid hours of searching the web (mostly this site) for answers. One thing I came across a handful of times was the the 1974-1976 Johnson 9.9 /15 HP engines just didn't do well with the Champion UL81C spark plugs. People found that engines that ran horrible, or not at all, on the UL81C's would run just fine on the NGK B7HS plugs. Being at the end of my rope with this thing, I figured it was worth a try. I hate to put plugs in a motor that are not called for by the manufacture, but all the stories I read matched mine to a T. I did a few checks to ensure that the NGK B7HS was as "equivalent" to the UL81C as possible and then went a got a set. She started right up and ran flawlessly when I went for a test ride.
Something obviously changed on my motor to have made the UL81C's perform badly (even a brand new set) because they had ran fine in the motor previously. However, whatever changed was very subtle and is not something that will show up through normal component checks. I may have been able to replace all 3 coils, both points, both condensors, and my wiring harness, and been able to run the UL81C's again, but its tough to throw that kind of money into an old motor - and then HOPE it fixes it.
And the best part is........ the NGK's cost half as much as the Champions where I bought them! For this particular make, model, and year of motor, the NGK plug seems to be the ticket. I was skeptical about the other peoples claims of how the plug swap solved all their issues, but now I've seen it with my own eyes.
Hope this helps someone.
Dale