86 115hp excess carbon on #1

[redjmp]

I dumped my autolube and always run premix so my plugs tend to run a little on the oily side.

New buhw's after 1 tank of gas shows lots of dry carbon collecting on only the top plug. The others are oily but no carbon build up.

New impeller and strong telltale...

Is this normal?

Cheers!

 

[Jlawsen]

Re: 86 115hp excess carbon on #1

The normal condition for a BUHW in a good running engine is light tan. It it's dry carbon then that could be the beginings of a slightly lean condition.

In trouble shooting these types of problems its always best to do the forensic's first. Run a compression test on all cylinders both cold and warm. You're looking for a significant difference in excess of 15% from original or 15% difference between any two cylinders.

Since it is only one cylinder, it's probably either a compression, cooling or spark issue. Reeds would effect 1 and 2 as well as a carb issue so I'm pretty sure you can rule them out. The motor has the switchbox/trigger/coil style ignition so you're lucky in that those parts are readily available if you need them.

I'm suspecting a cooling issue based on the plug condition. It's normal to have a carbon buildup on the piston top. Have a look and see if it's shiny and clean. That would indicate water intrusion, if theres an hourglass shape of cleaner area on the piston top that's usually a slightly lean condition and that could be from elevated temps in that cylinder.