4hp, 2010 Mercury Outboard, high idle, low idle, fail. Crash. Diagnostics?

frlrubett

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Leisure 23 came with an outboard which "had recently been serviced".

Day 1. New season, put some new oil and new fuel in the outboard. Cruised for 15km without issue, except the outboard cut out at when low in revs when warm. Also the red oil indicator light was blinking, was pushing into a 20knot wind with a 1.5knot tide engine was at full tilt for about three hours.

Day 2. Increased the revs via the idle screw, now in neutral the idle was good, not cutting out. Ran motor for 15 mins, did an oil change shut off.

Day 2 later in day. Cruised for about 15 mins, hoisted sails for two hours, then cruised back for 30 mins. Noticed the idle in neutral was much higher than when in gear, putting outboard into gear caused it to jump quite alarmingly.

Day 2 when back in port. Adjusted the idle screw again (engine hot this time) and the engine would idle nicely in neutral and in gear.

Day 3. Did not see any initial issues, cruised for about 1 hour but towards the end noticed that the engine cut out when the revs were low. Thought about messing with the idle screw again but got sort of used to it cutting out with low revs so thought I would live with it. Had a look at it and could see by the discolouration that the screw was actually set back to where it was on day 2 before the any adjustments - assumed it was just the engine coming back to life after winter.

Day 4. Started after three pulls, engine still cut out when the revs were too low, could not be bothered to mess around with the idle screw again, let engine warm up for 15 minutes. Headed out, three point turn to get out of marina, when changing from reverse to neutral noticed the neutral suddenly was over revving again. Had to go into forward gear to avoid reversing into a boat, lowered the revs as much as possible went into forward and the engine cut. Pulled the chord 10 times nothing whilst heading towards the pontoon in the tide, tried choke in and out, finally engine restarted but then cut out again. Gently hit the pontoon, got towed back to berth.

Day 4. Back on berth, tried restarting the engine to no avail. Checked the fuel, the oil, unplugged the auxiliary tank to use the internal tank. Engine did turn over a few times but didn't fire. Left it for a bit, tried again, managed to get it started but needed loads of revs to keep the engine going. As soon as I dropped the revs back down it died. Gave up.


Essentially, I am confused. One minute the idle is too low and the engine is cutting out so you have to rev slightly. The next at the lowest point on the throttle the engine is revving really high in neutral. Also, when the neutral is over revving you put it into forward gear and the idle in this gear is significantly lower. Any ideas?
 
Try a new plug
NGK DCPR6E ... I think ... check with manual. Gapped at 0.9mm

But I reckon the carb is probably in need of a clean but check the fuel system generally including in line filter and try pumping the priming bulb while using the remote tank
Check the float and needle valve and check that the needle is clipped to the float arm.
 
Yes. Idle problems and varying tickover point to a float chamber problem. Not assembled properly, needle jet worn, float punctured.
Possibly the slow running jet is a bit blocked. Could be a dirty fuel filter, but doesn't answer why the tickover alters.
 
Simple. The idle jet is clogged. If it is running OK at speed, that probably rules out plug, needle, float, and main jet... but no necessarily. It could be several of these acting together.

Pull the carb (2 bolts, 2 hoses, and the choke linkage), pull the bowl (2 screws), and remove the rubber plug in the center. The idle jet is under it and will come out with a small screwdriver. You will need a REALLY fine wire to clean it out, such as one plucked from a fine wire brush. While you're at it, clean the main jet (next to the idle jet) and spray out the whole carb (remove the top access plate (3 screws) for better access.

The idle jet is wee on small motors and frequently clog. It's too small to see light through.
 
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