Carbon build-up
 

Hetes the pistons after about 10k miles. Does this look excessive?
https://cimg5.ibsrv.net/gimg/www.hdf...178d46cb42.jpg
https://cimg6.ibsrv.net/gimg/www.hdf...eead8f4677.jpg

what octane and gas do you use?

The highest I can get here is 91.

How's your riding conditions?
Looks like a lot of stop and go build up.
It's never one thing-usually a combo of conditions.
https://www.hdforums.com/forum/touri...f-pistons.html
https://www.hdforums.com/forum/engin...cope-pics.html

Is your crankcase venting in to the AC or externally?

^This^

To the air cleaner. I need to mod it so it will vent to the ground.

That carbon build up has only a minor connection to octane. The higher the octane the slower the burn. The slower the burn the less of the intake charge is burned during the combustion cycle. So high octane has more deposits than the more complete burning lower octane. A fact of life that few folks know or understand.

It is primarily carbon mist build up from the oil mist taken into the intake from the routing of crankcase blow by.

Old school shade tree mechanic method of removal is to remove the air cleaner, run the engine at about 2K rpm and mist in water for awhile. The carbon with absorb the water and loosen. However do not listen to those that say after you do that go run the engine hard to blow out the carbon from the engine. What those folks don't know is that creates extremely higher combustion temps and will rapidly re harden the carbon. Go on mild runs and it will expel the loosened carbon. A good idea is to repeat about every 3K.

New school is to treat the gas with Chevron's Techron additive.

Or just do a mod to expel blow by into a catch can.

I run a little av-gas through mine just before an oil change

Couple of questions so I can better understand.

1. Does oil level play a role in build-up? Could over filling your oil reservoir, or not keeping it at mid-way on the dip stick play a significant role?

2. How about hard acceleration, good or bad as far as build up?

3. How about lugging the engine, does that have an effect?

On my new Iron, at 500 miles, I pulled the air cleaner off and I would say that there was maybe one drop of oil on the inside of chamber where the breather bolts enter the a/c housing. None on the filter medium itself, and the inside of the housing and cover were dry.