low revs after running

[JCasson]

Good Day - I have an 1988 F9.9G four stroke Yamaha outboard. It starts and idles well. After running for 4 or 5 minutes at higher revs it goes to lower revs ...(kind of like it miss fires. After a few minutes at the dock, the motor restarts and we repeat the process. I understand that the CDI does this if something is a not right to protect the motor. Dealer serviced motor - replaced oil press switch, thermostat, plugs, coil, CDI, impeller with no change. Will try ring free this weekend. This has been going on for a season and I would appreciate any ideas or suggestions...

 

[robert graham]

Are you sure your fuel tank is venting properly?...

 

[JCasson]

Yup - double checked that....

 

[JCasson]

Absolutely - I double checked that...

 

[JCasson]

Yup - double checked that - also tried squeezing the primer bulb while motor was at low revs..no change

 

[99yam40]

Have you tested anything ?
Or just throwing parts and money at the motor and hoping for the best?

Test the alarm system to see if it works like it should.
If overheat or oil pressure is calling for RPM reduction you should want to know about it, yes?

If that works and is not going off, then you need to be testing spark and timing when problem shows up to eliminate those

 

[JCasson]

No, I have not tested anything....tried to see if I could fit a gauge to check oil pressure, but dealer said this is not possible....don't know how to do these tests you suggest...can you point me in the right direction? Thanks