Re: 3 cyl 90hp merc jet drive
1-1/2 turns out is the starting point on all three carbs. A lot of times, the engine will run great right there, but you can change each screw about 1/8 of a turn at a time and see if you pick up any idle speed. My boat runs best at about 1-3/8 turns.<br /><br />Timing the engine can be done with a cranking speed check, with the throttles open, the tower shaft in the WOT position, and the spark plugs out, but grounded to the block. Timing should be 32 degrees BTDC. Under actual running condition, the timing will be 30 degrees due to the CD ignition characteristics.<br /><br />Timing at idle is 8 to 10 degrees and is adjusted using the throttle stop screw on the tower. It adjusts the idle timing though, not the idle speed. Make sure your follower roller is not touching the throttle cam during this test.<br /><br />Boat speed on a three cyl 90 will be a bit low. Speed can be a function of impeller to wear ring clearance, or ride plate position as much as anything. I think most owners are able to run a little faster, but it depends on your boat, and I'm not familiar with a xL 120.<br /><br />Oh... and buy a manual for your engine. From iboats, or your Merc store.<br /><br />Good luck
