Took the catamaran back out today after doing some adjusting on the engine that was giving me issues yesterday. While testing to see if my problem was fixed the other engine began to start running rough. Not only was it running rough but it now blows black smoke when reved and even leaves a trail of oil in the water. Please tell me there are other possibilities then a toasted engine. It will still fire up and the oil pressure is steady and holding about 70psi. Oil looks clean and full

I would do a compression test and leak down. Odds are it will render better answers than you will find here.

Sounds to me, like your carb has a piece of junk in it, flooding the engine, causing black smoke, and raw gas out the exhaust. That will leave a trail like oil will in the water.

Black smoke is a ton rich. The extra unburnt fuel is leaving those marks in the water.

If carb'd - get the carb apart and see what is flooding it. Look at needle and seat first. Trash will stick that open.

FI - get it scanned / then if you havwe to ck fuel psi / ck for stuck open injectors.

Gen 5 502 carbrated engines btw

Sounds to me like you need to step back for a second with this boat, and spend some time working on it, before taking it out again, and possibly doing permanent damage.

I would, do a full tuneup, plugs, wires, cap, rotor, fuel filters, etc. Go thru the carbs, check/set timing, . Then, go back out on the water.

You ever feel like your being echoed. LOL. Look at the time stamps. He,he

well....you're just obviously 1 step behind.....look at your join date, and look at mine....I got you beat by 4 months! almost 11 years here? Where does the time go?

Yup. Nothing but schitty advice so far.

I have done plugs, wires, cap, rotor, rebuilds on both carbs, complete fluid and filter changes all around and checked timing on both engines. The tanks were pretty nasty when drained the boat did sit untouched for 5 years. Debris is definitely possible.