After 50 miles I have a black Transom, is this normal in a Marine app, or this engine setup I built is running fat. Plugs are brown tan, not black. Runs perfect, my complaint is the suet.
Your thoughts are welcome. Just hate to lean her a bit and take out a valve or ring.. Mr. Bravo III
P/S plus the fuel economy sucks. 1 ML per GL

With my old boat, I'd have to wash the transom once a year. The question is if it's oil or fuel.

are you running carb ? maybe the choke is not pulling all the way off after warm up.or just set to strong for the temp.I backed mine all the way off and just give it two pumps to start and then sometimes have to feather it a bit to stay running till she wakes up,kind of like my girlfriend,hay honey it's time to play! if injected maybe the cold start is messing up some how.sencer,or control hope you get it under control been there done that soot thing.

It is a carbed engine with a MSD. No oil consumption ever. runs great. but if down wind you can get a wiff of richness i think. Just wish i could dyno the ***** in the boat under my severe
conditions. If i river hopp, I never seem to have any loading up problems either. Just after a trip of hard core run, i see the soot.
I can rite my name in it after 50 miles.

I would have to ask what do the plugs look like---rich or lean??? Then go from there.

test

checkmate454mag, plugs look perfect all the time, never seen any black, always brown to tan. Must be
rich only in mid throttle and up. Will try different carb and recheck for soot.

if its rich you can try a MSD ignition it cleaned mine up!!!!

I'd trust your sparkplug reading, that's the best indication of the engine combustion. Since you have a cruiser with a square transom I'd suspect some airflow issues directing the exhaust back to the transom. Have you thought about airflow around the transom and is it a possibility? Maybe some sections of PVC to extend your tips as an experiment, but I would not lean out the engine or you'll likely be wiping aluminum flakes from the transom.

Mine gets black if I burn higher than 87 octane, 89 isn,t too bad, though.