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Old 10-13-2016, 07:02 PM
Join Date: Jun 2008
Location: Christchurch, NEW ZEALAND
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Hi Franchi,

Some engines naturally run darker than others, likewise with some fuel blends.

So while an over compressed engine will always have a dark exhaust some under compressed or correctly compressed engines may also be quite dark.

You could try dripping some of the exhaust residue on a paper towel and leave it for a day or two. The oil will spread out leaving the carbon in the middle. If the oil at the edges of the puddle is a normal colour (dark honey or thereabouts) then you are probably fine, the dark colour is due to the carbon. You might see some shiny particles which may indicate aluminium rubbing.

I've found some kerosene produces a lot more carbon than others. Jet fuel runs a lot cleaner with less carbon on the piston and in the exhaust compared to hardware store kero over here, but Tim (quicksport2.5) hasn't found that to be the case in the States.

Maybe it'll clear up when the new pope is elected.

Dave H