Sheen in water after replacing carb

[JAC RMNF]

I have an 88 300 weekender with mercruiser 5.7s. Have recently replaced both carbs and now i have a sheen coming out of my starboard exhaust. Engine does not burn oil and i have not located any leaks. Im assuming this is fuel possibly from a leaking carb but they are brand new, Holley spreadbore. I know its limited information but has anyone experienced anything like this?

 

[markrsimon]

Could be a fault fuel pump. Check to see if you have a small clear hose that goes from the fuel pump up to the side of the carb. That hose should be empty - no fuel. If there is fuel in it, the diaphragm in the pump is bad, and excess fuel is being dumped into that small tube, which ends up being dumped into one of the barrels of the carb.

Other options are a sticky float, or float not seating - causing fuel to spill over inside the carb and into the engine.

Given you have two carbs, suggest swapping them to see if the problem follows.

If you have an oil cooler, pull the raw water lines on each side of the cooler and make sure things look okay there as well.

 

[dwna1a]

When was the last complete tuneup? Also i agree, could it be a split tube in the oil cooler or transmission cooler?

 

[JAC RMNF]

Have not noticed any oil or transmission fluid loss. Had no issues before carbs were changed. Guess I will have to swap carb from side to side and see if problem is the carb first.

 

[Mark.60]

Don’t get crazy until you do some troubleshooting.
Could be as simple as a choke plate out of adjustment causing engine to run rich.

 

[JAC RMNF]

Choke is functioning properly.

 

[Creekwood]

Maybe not at all the same, but on my last boat I thought I had a similar symptom. Light sheen on the water around the boat on start up and coming back to the slip. I thought for sure it was a carb issue, even though it seemed to be running fine. Turns out it was a very tiny leak in the trim cylinder hydraulic line on the I/O. More of a "seep" if even that. Of course you always trim the drive a bit in the slip and on start up I would trim it down. Then when the engine is running the exhaust bubbles up and over and around the cylinders and pulled minute amounts of the oil off the lines up. It fooled me into thinking it was fuel in the exhaust.

 

[JAC RMNF]

It's a direct drive inboard. But thanks. Had that issue on a 290 once. Always something

 

[LD Keller]

It's a direct drive inboard. But thanks. Had that issue on a 290 once. Always something

 

[LD Keller]

Mine was running rich... closed choke a bit and it’s much better

 

[JAC RMNF]

Mine was running rich... closed choke a bit and it’s much better

Choke is wide open. Changed the spark plugs today. They were 18 months old. Hopefully this will do it. Couldn't tell today because of muddy water and very high current.