Merc 4.3L I/O, 2001. Will Octane Booster help with gas that was supposed to be Premium but is not? Boat tends to run-on. I have changed thermostat, idle it for awhile before shutdown, and, normally, use premium.
Run some carbon blaster though it too. Run-on can also be caused by carbon deposits in the combustion chamber. Too low an octane will not cause run-on, just pre-ignition pinging.
Chipper,<br /> This is a common problem with this motor. Use premium fuel switch to one range colder on the plugs and make sure your timing is on the money. Merc has a bulletin out for this problem. The real reason this is happening is when GM switched to the vortec heads it bumped the compression up a little. This motor was designed to run with fuel injection and when merc used a carb they had to specify 89 octane. <br />I bet your engine compartment is small also. All of these things equal run on. If high octane and a decarb doesn't stop the runon try retarding the timing 1-2 deg from factory setting.<br />Good luck.
any of the store bought brands, absolutely not.<br /><br />only brand that has a significant effect would be those that contain MMT, I think NOS outlaw brand.<br />Very uneconomical though for a boat. Best to find 93 octane gas that is 93.
