Hi everyone, I'm really reaching out with this post as I'm at a point with my 1988 Mercury 60HP 2 stroke (OB240262) whereby I feel I'm chasing my tail and every step I take seems to produce more questions than answers. I'm a long way into diagnosis and part replacements but need some opinions from fellow marine folk who know their way around an outboard.
I posted on here a few weeks back with carb float issues which were quickly resolved and I was back on the water in no time and getting good performance from the old girl. Since then things have quickly gone wrong.
I could write a few pages on what I've been through already but I feel it best to explain the symptoms and list my trouble shooting steps and actions to rectify to try and keep this as short as possible which won't be easy.
Like I said, everything was running fine but after running for roughly 15 hours I was at full throttle at sea when suddenly the revs dropped from 5500rpm to 2500rpm but maintained that (at full throttle position) for a 15 min journey back to sheltered anchorage. As soon as I put it in neutral she cut out and after a few attempts I could start her but only on high idle. I was close to the harbour so I dropped my trusty Aux motor and made it back to the slipway. My first thought was fuel so I started my diagnosis at the tank which had a fresh fuel, the tanks are new as are the connectors, primer bulb and hoses and new water seperating filter so as suspected nothing was found here. I got to the fuel connector at the engine side and found the fitting wasn't actually clipped on properly although it looked fine to the eye and no sign of a fuel leak when primed. The engine side fuel connector looked worn so I replaced that with an original part and while I was there I decided to look at the entire fuel delivery system and replaced all hoses, rebuilt the fuel pump and replaced the inline fuel filter. The carbs had just recently been rebuilt with a genuine kit and held pressure when primed without leaking so I thought my problems would be over. I made some final adjustments to the carb whilst on the water to bring the idle within range and made my way out to sea which is a 30 min journey at 4 knots. As you approach the harbour entrance speed can be increased to 8 knots, which I attempted to achieve, but as soon as I increased power the engine stumbled to the point of stalling but would fire and run if I pulled back slightly on the throttle to a maximum of 2000rpm, any more than that and it would almost stall. It didn't feel good and it certainly wasn't calm at sea so I turned around in the main channel and started to head back. The engine then quickly surged a few times and then cut out in a fast flowing narrow channel so before I deployed the Aux motor I attempted a restart and to my delight she fired and I quickly put her in gear back to 2000rpm and made the 30 min journey back to the slipway. I didn't attempt to increase or decrease power on this journey but I did notice that the throttle position was further forward than normal for the RPM given. I have a very generous test tank at home so I decided that until I was convinced this issue was resolved I would fault find there until I resolved the issue. That was 3 weeks ago and upon close inspection I noticed the following on my trouble shooting journey:
- I can prime the fuel system until the bulb is very firm and no fuel leaks are detected.
- Follow normal start up procedure with high idle lever in position and she fires as normal but very smokey.
- Runs at idle (1000rpm) for 2 to 3 mins, lots of exhaust smoke, and then stumbles and cuts out.
- Will only restart on high idle but will restart straight away, cuts out though as soon as fast idle lever dropped.
- Idle speed screw adjustment makes no difference and as I turn to increase idle it almost instantly drops revs until I've almost used all of the available screw thread and then cuts out.
- Idle air screws in carbs turned out to factory.
- When outboard inspected after cutting out without Cowling off and carb throats exposed I notice a slow stream of fuel running down the carb throats and pooling at the front of the carb throats before dripping out. I can soak this up and within a minute the pooling stops and doesn't return until the engine is either cranked or run and then stopped. The bottom carb is worse than the top carb.
- Spark checked with generic tester which looked to produce spark on all three cylinders but touching the plugs when it's just cut out tells a different story. Top plug feels normal temp, middle plug feels warm but not normal and bottom plug is cold.
- Plug electrodes tell the same story, and not a good one. I have tried to attach a picture but it won't let me upload any more photos. Plug 1 wet fouled, plug 2 oily deposits but not as fouled as no.1, plug 3 like it's never seen spark of fuel in its life!
- Swapped coil positions to see if the issue moved. Swapped no.1 for no.3 but made no difference to the results.
- Held a piece of card in front of the carb throats while running and no fuel seen spitting back.
- Big oily mess left in test tank afterwards and when drained I've even noticed fuel dripping from the prop followed by an abnormal amount of thick oily 2 stroke sludge that runs for quite some time afterwards.
Here's a quick list of parts that have been replaced on the powerhead within the last 4 months leading up to the first sign of trouble for either regular maintenance or repair:
- Spark plugs
- Fuel pump rebuild
- Fuel filter
- fuel tank connector
- All fuel hoses and clamps
- Carb rebuild from kit / set float height
- Carb body put through ultrasonic cleaner
- Baffle plate gaskets replaced (piston rings looked to be in good condition)
- New CDI switchbox
- Endoscope through spark plug holes / piston crowns showed normal carbon deposits but in overall good condition.
- Compression checked / 115psi on all 3 cylinders.
- Spark tested on generic plug tester / spark detected.
I've been focused on the fuel system, and then the electrical side but apart from a standard multimeter my test equipment is limited which is why I've stopped at the coil swapping which didn't yield any results. I'm also thinking is this more than one problem that I'm chasing.
If compression is good and spark tester shows action why is there such a temperature difference between plugs? And why doesn't this move when I switch coil position?
Why does it appear to run so ridiculously rich even when I adjust to a leaner position than stated in the manual?
If carbs / fuel system have been overhauled and system can be primed without leaks why is there fuel collecting in the carb throat after cranking or shutdown?
Why is there such a huge oil slick in the test tank and resulting fresh fuel and oily sludge dripping from the prop after shut down? Its actually started to take the paint finish off the prop!
I posted on here a few weeks back with carb float issues which were quickly resolved and I was back on the water in no time and getting good performance from the old girl. Since then things have quickly gone wrong.
I could write a few pages on what I've been through already but I feel it best to explain the symptoms and list my trouble shooting steps and actions to rectify to try and keep this as short as possible which won't be easy.
Like I said, everything was running fine but after running for roughly 15 hours I was at full throttle at sea when suddenly the revs dropped from 5500rpm to 2500rpm but maintained that (at full throttle position) for a 15 min journey back to sheltered anchorage. As soon as I put it in neutral she cut out and after a few attempts I could start her but only on high idle. I was close to the harbour so I dropped my trusty Aux motor and made it back to the slipway. My first thought was fuel so I started my diagnosis at the tank which had a fresh fuel, the tanks are new as are the connectors, primer bulb and hoses and new water seperating filter so as suspected nothing was found here. I got to the fuel connector at the engine side and found the fitting wasn't actually clipped on properly although it looked fine to the eye and no sign of a fuel leak when primed. The engine side fuel connector looked worn so I replaced that with an original part and while I was there I decided to look at the entire fuel delivery system and replaced all hoses, rebuilt the fuel pump and replaced the inline fuel filter. The carbs had just recently been rebuilt with a genuine kit and held pressure when primed without leaking so I thought my problems would be over. I made some final adjustments to the carb whilst on the water to bring the idle within range and made my way out to sea which is a 30 min journey at 4 knots. As you approach the harbour entrance speed can be increased to 8 knots, which I attempted to achieve, but as soon as I increased power the engine stumbled to the point of stalling but would fire and run if I pulled back slightly on the throttle to a maximum of 2000rpm, any more than that and it would almost stall. It didn't feel good and it certainly wasn't calm at sea so I turned around in the main channel and started to head back. The engine then quickly surged a few times and then cut out in a fast flowing narrow channel so before I deployed the Aux motor I attempted a restart and to my delight she fired and I quickly put her in gear back to 2000rpm and made the 30 min journey back to the slipway. I didn't attempt to increase or decrease power on this journey but I did notice that the throttle position was further forward than normal for the RPM given. I have a very generous test tank at home so I decided that until I was convinced this issue was resolved I would fault find there until I resolved the issue. That was 3 weeks ago and upon close inspection I noticed the following on my trouble shooting journey:
- I can prime the fuel system until the bulb is very firm and no fuel leaks are detected.
- Follow normal start up procedure with high idle lever in position and she fires as normal but very smokey.
- Runs at idle (1000rpm) for 2 to 3 mins, lots of exhaust smoke, and then stumbles and cuts out.
- Will only restart on high idle but will restart straight away, cuts out though as soon as fast idle lever dropped.
- Idle speed screw adjustment makes no difference and as I turn to increase idle it almost instantly drops revs until I've almost used all of the available screw thread and then cuts out.
- Idle air screws in carbs turned out to factory.
- When outboard inspected after cutting out without Cowling off and carb throats exposed I notice a slow stream of fuel running down the carb throats and pooling at the front of the carb throats before dripping out. I can soak this up and within a minute the pooling stops and doesn't return until the engine is either cranked or run and then stopped. The bottom carb is worse than the top carb.
- Spark checked with generic tester which looked to produce spark on all three cylinders but touching the plugs when it's just cut out tells a different story. Top plug feels normal temp, middle plug feels warm but not normal and bottom plug is cold.
- Plug electrodes tell the same story, and not a good one. I have tried to attach a picture but it won't let me upload any more photos. Plug 1 wet fouled, plug 2 oily deposits but not as fouled as no.1, plug 3 like it's never seen spark of fuel in its life!
- Swapped coil positions to see if the issue moved. Swapped no.1 for no.3 but made no difference to the results.
- Held a piece of card in front of the carb throats while running and no fuel seen spitting back.
- Big oily mess left in test tank afterwards and when drained I've even noticed fuel dripping from the prop followed by an abnormal amount of thick oily 2 stroke sludge that runs for quite some time afterwards.
Here's a quick list of parts that have been replaced on the powerhead within the last 4 months leading up to the first sign of trouble for either regular maintenance or repair:
- Spark plugs
- Fuel pump rebuild
- Fuel filter
- fuel tank connector
- All fuel hoses and clamps
- Carb rebuild from kit / set float height
- Carb body put through ultrasonic cleaner
- Baffle plate gaskets replaced (piston rings looked to be in good condition)
- New CDI switchbox
- Endoscope through spark plug holes / piston crowns showed normal carbon deposits but in overall good condition.
- Compression checked / 115psi on all 3 cylinders.
- Spark tested on generic plug tester / spark detected.
I've been focused on the fuel system, and then the electrical side but apart from a standard multimeter my test equipment is limited which is why I've stopped at the coil swapping which didn't yield any results. I'm also thinking is this more than one problem that I'm chasing.
If compression is good and spark tester shows action why is there such a temperature difference between plugs? And why doesn't this move when I switch coil position?
Why does it appear to run so ridiculously rich even when I adjust to a leaner position than stated in the manual?
If carbs / fuel system have been overhauled and system can be primed without leaks why is there fuel collecting in the carb throat after cranking or shutdown?
Why is there such a huge oil slick in the test tank and resulting fresh fuel and oily sludge dripping from the prop after shut down? Its actually started to take the paint finish off the prop!
