Johnson/Suzi 225 4 stroke running problem
I have on the back of my rib a Johnson 225 4 stroke outboard (which is a rebadged suzi). It has run fine ever since we've had it, until recently. The problem started with it not running at high revs. Sometimes (normally after it had been running for a little while) it would stutter when you gave it more throttle, although pulling back on the throttle a bit would make it run ok again. This would normally happen at around 3000rpm. The problem has got worse, with it happening at lower revs. Now when you give it more throttle it just splutters a lot and goes down to idle speed and doesn't sound happy at all.
I have had SEA marine look at it, who thought it was the thermostat making the engine go into gaudian mode. A diagnostic check showed no errors at all - the engine "thinks" its ok. After the thermostat was tested it was concluded that that wasn't the problem. I then took the boat out of the water, and took it to Fairweather. Again, they hooked it up to a computer and it came back with no problems. It was still misbehaving though. Fairweather's only suggestion was that maybe the plugs needed chaning, so we did that, and still nothing. I have since replaced two fuel filters, and various other bits of "pluming" in the hope that that might cure it. It hasn't.
Has anyone got any suggestions. To recap the problem normally comes on after a little while of running. This seems to vary from a few minutes to maybe half an hour. The problem seems to be getting worse in that when the engine starts dying, it is revving less and less as the problem continues. As I said it's when you throttle forward, but it seems to improve when you throttle back - its almost like the engine is being flooded or something.
Any suggestions until the mechanic can have another look at it would be greatfully received!