Help Tohatsu 60 automix keeps dropping power after 30 secs at top end

My Tohatsu 60 auto mix 2005 model has developed a fault that no one seems to be able to fix. It went in for a service and ended up having £600 worth of work done to it and has not run right since. During the service the carbs were removed and cleaned as well as usual service etc. the engine runs well now except once the boat sits up on the plane at 5000rpm you only get about 30secs of full power before it starts hunting and throttles back to 3000 then 2000. If you then idle after a minute or two you can come up in power only for the same thing to happen again. It feels like fuel starvation so I changed tank, hose connectors, fuel pump, fuel filters and removed and checked all rubber hoses on engine and still the same! I did find that the kill circuit had a screw accidentally embedded in it (during the service) which I removed and repaired. The place I had it serviced at are no help what so ever and when I fined the problem if it's there doing I will seek a refund. I am into this a £1000+ nearly as much as it's worth and would really appreciate some help. The fault only occurs under load.
thanks for taking time to read this

I assume your model is M60C (year is unimportant). You could have an alarm going off, causing limited RPM, or it could be almost anything -- even ignition -- not just fuel. Was it running right before being serviced? Do we know, aside from cleaning carbs, what work was done? If it was OK before, and poor now, it's likely that the repair work has contributed to the issue. Inadequate cooling can cause RPM limiting. Is this a Remote or Tiller model? Are there any fault indicator lamps coming on? Is the oil system working, was it bled correctly?

pvanv said:

I assume your model is M60C (year is unimportant). You could have an alarm going off, causing limited RPM, or it could be almost anything -- even ignition -- not just fuel. Was it running right before being serviced? Do we know, aside from cleaning carbs, what work was done? If it was OK before, and poor now, it's likely that the repair work has contributed to the issue. Inadequate cooling can cause RPM limiting. Is this a Remote or Tiller model? Are there any fault indicator lamps coming on? Is the oil system working, was it bled correctly?

Click to expand...

Hi it is the M60C model. The fault was not there before service and the ignition was altered during service. It doesn't feel like a rev limiter and being as you can go back up in power 2 mins later I am dubious to think temperature. It is remote controlled. There is no warning lamps lite but I am dubious now of standard of work so I am not sure if it was bled correctly.

Best to test ignition and fuel, then mechanical systems. Could still be a fuel problem...