I need some help tuning the engines in my commander. I purchased a '73 36' sportfish in July and am experiencing a steep learning curve. My last boat was a '67 31' express hardtop. I just about had the 327's mastered when I sold her. Anyway, here is my current situation:
P.O. allowed the boat to sit for quite some time. There is quite a bit of varnish in the tanks, evidenced by the black syrup that leaked out of the throttle shaft onto the port intake manifold. Performance deteriorated steadily from the point of sea-trial to the present in both engines. Top rpm declined to around 2000. I noticed fuel in the oil on the port side, subsequently removing > 5 gallons of the mixture from the engine. I'd like to focus on the port side. I anticipate that the fix for that side will apply to the starboard.
Since discovering the mixture, I have:
1. Replaced all ignition parts (plugs, wires, coil, button (mallory 319), and cap). Electronic ignitions are already installed.
2. Timed engine to top dead center at ~700 rpm. I could not get the engine to maintain 500 rpm, as specified in the manual, for the setting.
3. Replaced the fuel pump with the model recommended by several on this site mj6409?? I cant remember exactly what the model number was. After installation, I discovered that I still had liquid fuel pouring in the manifold at idle.
4. Submitted carb to shop for rebuild. After a soak, the specialist reported that the amount of pitting in the aluminum made a rebuild inadvisable. So, I replaced it with an Edelbrock 625cfm marine carb. 1409???
I am treating the tanks with starbrite tank cleaner and enzyme formula. I am tuning the engines from a fresh jug of 93 octane fuel that bypasses my fuel water separator, but not the ard-mounted filter. Hopefully, I can avoid blaming current issues on the dirty fuel.
Just before I replaced the carb, I began experiencing a backfiring condition, especially at low rpm's. It continues with the new carb. I have verified the firing order. Set the timing as close to top dead center as I can. (I've also adjusted the timing while the motor is running.) I've played with the idle mixture settings on the new carb. Engine runs without much change, even if screws are turned all the way in. Fuel pump pressure has been confirmed to be 6.5 to 7 psi. Exhaust smells rich.
About the only (easily adjustable) variable that I have not manipulated is the valve setting. Can mis-adjusted valves cause a backfire? Could this also contribute to the rich condition? Does anyone have a similar experience? I'm running short on options.