My first post on this site, hopefully someone will recognise my problem.
The engine is a 1995 Magnum 350 (carb). It starts easily and runs smooth all day at all speeds, I can stop and start several times and it never fails to start. I can use it at full throttle or cruise at around 18-20 mph no problem. But after a long run back through the harbour at 15-20 knots, we slow down to around 6 knots for the final stretch, at this point any adjustment to the throttle will cause the engine to run rough or sometimes it will just start to run rough by itself. It will backfire and ultimately stall and will then fail to start until it has been left at least 10-15 minutes. When the engine does start, it runs smoothly with no load, but once in gear it still runs rough, and if we slow down to 4 knots it will stall. This only seems to happen at the end of the day after the 30 minute slow part of our trip. I have changed the water/fuel separator but nothing else so far. The engine was taken out by my local mercruiser dealer over the winter for a new transom./gimbal assembly, they checked the plugs and said they were fine (the plugs have only done around 3-4 hours since they were fitted last year). There was fuel left in the tank from last year, but I put around 90 litres of fresh fuel in before going out. I dont know how much was still in the tank because the fuel guage is dead.
Thanks in advance for any help.
The engine is a 1995 Magnum 350 (carb). It starts easily and runs smooth all day at all speeds, I can stop and start several times and it never fails to start. I can use it at full throttle or cruise at around 18-20 mph no problem. But after a long run back through the harbour at 15-20 knots, we slow down to around 6 knots for the final stretch, at this point any adjustment to the throttle will cause the engine to run rough or sometimes it will just start to run rough by itself. It will backfire and ultimately stall and will then fail to start until it has been left at least 10-15 minutes. When the engine does start, it runs smoothly with no load, but once in gear it still runs rough, and if we slow down to 4 knots it will stall. This only seems to happen at the end of the day after the 30 minute slow part of our trip. I have changed the water/fuel separator but nothing else so far. The engine was taken out by my local mercruiser dealer over the winter for a new transom./gimbal assembly, they checked the plugs and said they were fine (the plugs have only done around 3-4 hours since they were fitted last year). There was fuel left in the tank from last year, but I put around 90 litres of fresh fuel in before going out. I dont know how much was still in the tank because the fuel guage is dead.
Thanks in advance for any help.
