Hi all,<br /><br />I have a problem that started after vinter storage of the motor this year. The proble is always there<br /><br />Failure indications:<br />- Reduced power (may be 30 % or so) during acceleration from zero to full speed.<br />- Full speed used to be 5500 rpm and 31 knot. mow only 5000 rpm and about 26-27 knots.<br />- When motor reach 5000 - 5200 rpm you can hear that it is kind of trying to proceed to increase its rpm, but it instead falls back 100 rpm or so. Occationally it has reached 5300 RPM but steady state is never more than 5000 rpm.<br />- When very slowly decreasing boat speed from full, when down to about 3500 - 4000 rpm and maybe 15 knots, suddenly an increase of power takes place, as if it suddenly became normal. (primarily noticed by sound)<br />- <br />Everything else is normal:<br />- Motor stars excellent as allways<br />- Idle is normal<br />- Lowspeed to medium speed seem to be normal<br /><br />Log of events since it worked normal, wich was until i Took it out water for vinter storage:<br />- Took the boat and motor to Yamaha workshop for vinterservice/maitenance and motor konservation<br />- The motor was taken ofthe boat<br />- The workshop did vinterservice (looked afterthe motor in a professional way)<br />- In may I trailered the boat to the workshop and the put back the motor on the boat again.<br />- I then replaced (for the first time) the water separating filter in the boat (fixed tank in the boat)<br />- After some pumping on the rubber pump i started the motor and took a testrun. Then I noticed the problem as described above.<br /><br />What I have done:<br />- Tried with a separate tank direkt to the motor. No change<br />- Ispected and changed spark plugs. Looked quite normal and all looked the same. Also have inspected the immediately after 8 min at full speed. Normal.<br />- Replaced fuel pump diafragm (not damaged thogh)<br />- Disassebled carburators and blow everything with compressed air<br />- Inspected all mekanikal linkage in the motor. seemed normal and working. Inkluding normal behavior of carburator moving parts.<br /><br />No change at all after above overhaul!<br /><br />Can it be the ignition/CDI-box<br /><br />Or does it sound like air coming in to the fuel system before the fuel pump?<br /><br />Anyone has an idea???<br /><br />Motor facts:<br />- Yamaha 70 BETOL modell 1997<br />- Not very much used, well taken care of<br /><br />Berra
