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BF40 Honda Limp home mode

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fishingdale

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I have a small tinnie with a 2005 BF40 Honda 4 stroke on it. Over the last 6 months or so It has encountered a repetitive but intermittent fault. After running for 30 min or so at med -high speed it drops in revs and starts running rough. At first it was of night time and always on the way home. First I thought it was water in the fuel, while bobbing around a few mile out I drained the carbie bowls, flushed the filter with no result. Limped home @ about 6 knots. Relaced fuel filter, cleaned tanks, checked plugs and added an extra fuel filter. A couple of trips later same problem. It was due for its annual service so I took it in to the local honda dealer $550 later, took it out with the same result. Took it back, was told they had put the wrong thermostat in it and it was now all good. Went out same problem. Seems to be heat related because it only happens when it has run for a while and once cold resets. It has never had an temp alarm come up. Im thinking maybe a sensor or control card. Has anyone experienced this before.
 
I would still perhaps be suspicious of the thermostat, i could still be wrong, or very blocked. This is very easy to check and change yourself, but you do need to replace the orings so get those from your dealer first. My thermostat looked terrible, though I don't know how old it was, I think it was original.
 
Thanks Chris, I have observed the thermostat open approx 1 min after starting, it has good flow and they have given me the thermostat and impellor after each service, also the water from the tell tail is cool and I have never got a temperature alarm. I might put one of the old ones back in to make sure its not that.
 
Sometimes intermittant problems like that are electrical. Motor gets heated up and an electrical connection breaks down. Check and clean all your electrical connections and test your plug wires for too high resistance.
 
Although you seem to have covered the fuel system there are still a few things I would do.

Next time there is an issue pump the fuel bulb and see if it needs much pumping to get it firm and when doing so does it fix the problem (possible air leak in the boats fuel system)

If you have warning indication lights what lights are on and what lights are not? This makes a big difference in diagnosing the problem

Garry
 
Thanks Garry, I have tried that a couple of times, the bulb has fuel in it but not overly tight. When I squeeze it while it was running in the "limp state" it made no difference to how the outboard ran, nor did the revs change. It has temp and oil alarm and warning lights, non have gone off, the dealer found no alarm faults when it was in getting serviced either. I can normally nut these things out but this one has me stumped. Frustrating, only a few weeks before the snapper close season.

Dale
 
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Hi Dale,
One thing you might try is to (following chawk_man's suggestion here) disconnect and reconnect your engine control module. I have been using a spray called
DE-OXIT on these connectors that I buy from the music store that is used to clean instrument sockets and connectors on guitar amps. I have found through trial and error that these engine power "de-rate" systems do not like oxidized connections. Worth a try if all else fails.
 
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