1993 Mercury 90 HP with idle problems

I have a 1993 merc 90 hp, 3 cylinders. I have owned it since 1997 and never had any problems with it. I troll a lot, 6-8 hours a day, about 10 times a year. Lately it just will not idle and I have to move throttle forward every time I start it. I changed the plugs which were loaded up and this helped, but after 3 hours of trolling it would not idle again. I took it to the ramp and sprayed a whole can of engine cleaner in the carbs and waited 12 hours and went back to the ramp to run it out. (Followed can directions). I then changed the plugs again and went to the lake to adjust the mixture on the carbs. It started good and idled. After warm-up, I started on the number 1 carb and rotated screw with spring clockwise until I wanted it to choke. Well I got too excited and rotated it all the way in until screw stopped and nothing happened to the engine and I lost track of turns also. The engine was still running. So I backed it out 1.5 turns (just guessing) and thought I would start on the middle carb. This carb did like it was supposed to and started to choke, so I rotated it 1/4 turn counter clockwise. I can't remember what happened next but it seemed I just lost all previously set positions on carbs, so I just set them all to 1.5 turns.

This setting seemed to work ok as I tested acceleration and Idle. I then lowered the idle speed because I was over 3.0 MPH (GPS) at idle in gear. I put the tack on the top cylinder and could not get the engine to go lower than 1200 and continue to run with out cutting out. I got it to 2.5 MPH. I played with the mixture screws backing them all out to 1.75 and tried it again. It got a little better, but no where near the 700-800 rpm idle speed in gear against water that manual called for. Could not get tach down to 1000

Questions - Why wouldn't the number 1 cylinder choke out? How can I get this engine to idle slower according to manual 7-800 rpm?s? What testing procedures should I do to fix this...Easy to more difficult? I was thinking about doing all the resinking carbs, timing, timing advance etc tests in the manual except I don't have the Timing gauge to find TDC and then 2 degrees off. Any other procedures that can do this? My last resort is to take all the carbs apart and clean!

Re: 1993 Mercury 90 HP with idle problems

May want to de-carb with Sea Foam in gas. Allot of trolling means allot of tarnish. Look at the FAQ section on how to de-carb with the gas method since you allready tried the spray method in little results. The idle screws sould be turned out 1.5 turns each to start with then fine tune it.

Re: 1993 Mercury 90 HP with idle problems

Most likely, the needle check valve on #1 carb float is worn or stuck and the carb is flooding. You should have WME carbs on it and there's nothing to rebuilding them except making sure all the tiny passages are blown out, The rebuild kits are cheap and include a new floate needle valve with neoprene tip. Make sure to set the float height to 7/16". If you do one, do all three.

Hint: Mark the carbs 1,2,3 (Some are already marked from the factory) with a scribe before you remove them. Do one carb at a time, soak them in Gunk Carb Cleaner overnight and never mix parts.

Take adavantage of the opportunity and rebuild your fuel pump and accelerator pump (if so equipped). Also replace all the fuel lines with E10 rated tubing.

When you're done either do the Link and Synch yourself or take it to a shop.

The total cost won't be over $100.00.