My 1986 18ft Wellcraft has an Alfa One 170 Mercruiser power package. The engine model is MCM 170, serial B406627. This engine has over 650 hours.
The symptoms are backfiring through the carburetor, and sometimes stalling when the throttle is suddenly opened from idle speed to full throttle (when pulling a skier on a deep water start).
The spark plugs are coated with a dry black soot as with a rich fuel mixture.
When running it in my back yard, The exhaust is sooty. The black soot can be seen floating on the heat exchanger raw water discharge.
The engine lubricating oil is blacker than it has ever been in the last fifteen years.
I cleaned and gapped the spark plugs but after running the engine for only 15 minutes the plugs were again sooty.
I took a compression test and each cylinder read 125 PSI. 5 years ago they read 145 PSI.
I pulled the 1/4 " NPT plug from the intake manifold and noticed raw gasoline in the bottom of the manifold. I connected a vacuum gauge and got a reading of about 10 inches. The gauge indicated late valve timing. I adjusted the ignition timing to specs, and the carburetor to obtain the highest vacuum reading. The vacuum rose to about13 inches, indicating late ignition timing. The intake manifold gasket isn't leaking (allowing air to enter the manifold downstream of the carburetor). The fuel is clean and free of water.
The engine doesn't idle roughly as with a leaking needle and seat, yet the soot on the plugs seem to indicate a rich fuel mixture.
Does the carburetor seem faulty? Is the valve timing actually late? Or is the engine just plain worn out.
What do you think? Please help.
Thanks, oldmike
The symptoms are backfiring through the carburetor, and sometimes stalling when the throttle is suddenly opened from idle speed to full throttle (when pulling a skier on a deep water start).
The spark plugs are coated with a dry black soot as with a rich fuel mixture.
When running it in my back yard, The exhaust is sooty. The black soot can be seen floating on the heat exchanger raw water discharge.
The engine lubricating oil is blacker than it has ever been in the last fifteen years.
I cleaned and gapped the spark plugs but after running the engine for only 15 minutes the plugs were again sooty.
I took a compression test and each cylinder read 125 PSI. 5 years ago they read 145 PSI.
I pulled the 1/4 " NPT plug from the intake manifold and noticed raw gasoline in the bottom of the manifold. I connected a vacuum gauge and got a reading of about 10 inches. The gauge indicated late valve timing. I adjusted the ignition timing to specs, and the carburetor to obtain the highest vacuum reading. The vacuum rose to about13 inches, indicating late ignition timing. The intake manifold gasket isn't leaking (allowing air to enter the manifold downstream of the carburetor). The fuel is clean and free of water.
The engine doesn't idle roughly as with a leaking needle and seat, yet the soot on the plugs seem to indicate a rich fuel mixture.
Does the carburetor seem faulty? Is the valve timing actually late? Or is the engine just plain worn out.
What do you think? Please help.
Thanks, oldmike
