Spark Plug problems.

[Julio A.]

My old Plugs died. I replaced it with new bosch Super fours and ran the bike around the expressway today. Upon Arriving, I removed the plugs and found out the the right side plug is heavily fouled with an thick, almost shiny black layer and the threads have an unknown black liquid almost oil like stuff on it's threads. But the left side plug looks alright although there are some white ash residue.

I know It could be running rich. But I have just set the a/f mixture screw and both carbs have the same number of turns. My exhaust does not blow smoke; which I think removes the possibility of oil entering the combustion chamber.

Oh, and it's ok to use a plug one step hotter than OEM right?  

[Barry]

The mixture has to be grossly rich to blacken a plug as you have described and if one cylinder is that rich the engine won't run right. In my experience if the engine is running well black plugs are more likely to be result of using the choke or burning oil and your description sounds like oil.

BMW will have conservatively specified the original plug to be safe at sustained high speed and engine load at high ambient temperatures so provided you never run the engine like that a one grade hotter plug will probably be OK as long as the mixture is not too weak. I'm happy to do that with standard single electrode plugs anyway. I don't know anything about the heat range of super fours though.

[Julio A.]

I'm fearing that the piston rings are shot. I'm still looking for more simpler problems. Is it possible that the oil from the breather is enough to cause that? I am using the choke quite frequently, but shouldn't be the left cylinder be carbon fouled as well?

[Bob_Roller]

Just a note on carb tuning, you have to adjust each carb to where each cylinder is running correctly, adjusting both mixture screws to the same number of turns may not be the best setting .

I agree with Barry about the 'choke', check to make sure it is returning to the stop when you move the 'choke' lever to the off position .

[Barry]

Julio

I you have a very slim torch or light source of some sort remove the plugs and take a look down the hole at the piston top to see if there are any differences side to side. I use an led wand that actually fits through the hole to give a really good view. If the right plug was fouled with oil the piston top will likely look wet and looking down between the bottom edge of the piston and the cylinder wall you may actually see some oil. The other side by comparison will probably look dry.

[Olliepup]

Barry means a slim "flashlight". A British "torch" is a flashlight on this side of the pond.

[Barry]

1.torch  A portable light produced by the flame of a stick of resinous wood or of a flammable material

...mmm  putting one of those near the plug hole wouldn't be a smart move - thanks for the translation Wavy Dave