Carbon buildup on piston/head on continental gas

[Forester Massey]

About a year ago I completely rebuilt my 135. New pistons, sleeves, values, the works. Due to a severe exhaust valve leak (undetected when putting back together) I had to pull the head off to do a credible job. What I found was what I consider an excessive amount of black carbon on the head and piston. Way more than what I would expect for a newly rebuilt engine with 100 hours. The plugs looked good.

As some background. I installed a flame thrower coil and pointless ignition which has greatly increased the spark. I have used 100% gas throughout its 100 hours. The carb has been adjusted to what i consider to be normal but is my mixture too rich?

Lastly, I was looking down into the intake port of the manifold. Have any of you ever looked down into the hole where the carb attaches? When I shined a light into it I found a piece of cast metal obstructing the intake to some extent. It was open partially on the sides and very jagged. If it was meant to be there its quality is awful. Its almost as if its meant to direct the gas fumes toward the outside of intake but it sure does not look normal. Is it possible during the casting this piece was left behind? I was expecting the intake tube to be open.

Any help would be appreciated.

 

[Kenneth S]

A 100 hours in a year that's not a lot of run time, it also depends on how you used it. If its run at part throttle mostly, and only ran for 30 minutes at a time it's going to have more carbon than if it was run wide open for hours. The continental engine is not the most fuel efficient engine in many ways due to its design. As the intake goes I've never really paid attention to the inside of one since it's not made for high rpm use.