'05 340 Sundance with 8.1 Horizons. Last outing I noticed the port engine was slow to get to the same rpm (3450 cruise) as the starboard. It also required noticeably more throttle to match the starboard. Suggestions on where to start checking? Engine starts with no problem. Runs smooth and all temps and pressures good. Plugs? Injectors? Cool fuel module issue?
Check the look fuel canisters. Merits painted the inside and with the enthanol it eats the paint and you get chips clogging the filter. On top of the kook fuel is a little filter two screws hold it on place. Take the little hose off and pull the filter see if there are any paint chips. If there are you may have to get new look filter canisters.
Similar problem at about 150 hrs on the engines; starboard required more throttle than the port to sync RPMs. I was told by our Mercury Marine Service folks that the 8.1's eat the iridium plugs. After replacing all 16, the throttles are in sync.
I had a similar issue on an '01 340 and noticed one engine running a little rich (heavy exhaust smell around the dock even after reaching temperature.) Noticed the occasional oil drip would get into the temp sensor connector located under the oil filter. After cleaning the connector the problem went away.
