Yamaha 75 hp 2 Stroke Wont go above 3300 rpm Under Load

[Bigplumbs]

We tested the new XPro 535 today and all went very well. The initial run of about 2KM the engine reved fine and the boat easily reached over 30 knots.The revs were at about 5600 (Not full throttle) and all running fine

Then on the third run the engine would only get to about 3300 revs.

This is a new built boat so has new fuel tank vents open. New/Fresh E5 Fuel, New 8 mm bore fuel line and new Yamaha connector.

When I got the boat home on the the Trailer the engine would easily reach 6000 + rpm on the lever and also on the Throttle in gear.

This is a 2005 Yamaha 75hp 3 Cylinder Oil injected 2 Stroke.

Any help would be appreciated as to why it would not go over 3300 rpm under load after it had been going so well

Thanks

 

[julians]

When I've had an outboard that won't rev under load it's been due to worn out sparkplugs or ht leads that are breaking down.

 

[Momac]

Engine very bad

 

[Rappey]

Then on the third run the engine would only get to about 3300 revs.

Did you try turning it off and back on again?
Does it have alarms for overheating, high voltage etc? These can certainly slow one down. Not sure of the monitoring for a 2t.
That is a strange problem to have.

 

[Bigplumbs]

I think I have tracked it down to it going into reduced rpm mode or limp mode. From what I have read it does this for 2 reasons. Too hot or 2 stroke oil low. My oil level is fine but I also understand the oil sensor can be an issue also the float in the oil tank.

I also understand that the temp sensor can cause issue. I now certainly have some things to work on. Issue is I have not much time before I was intending to take it on our second Scotland trip

 

[Bigplumbs]

So doing a little more investigation I checked the Thermostat and that was working fine. Started opening at around 58 degrees C so I decided to see if I could test the temp sensor that goes to the ECU.

It was quite easy to get out but as I gently tried to unplug the black with the pink wire broke at its plug. I was not putting any real force on the pink plug. The break point is corroded. Now as these I think measure resistance at different temps and report this back to the ECU I am wondering if this bad joint could have been messing with the resistance.

Here is a pic of the broken wire on the part.

What do others think

 

[julians]

So doing a little more investigation I checked the Thermostat and that was working fine. Started opening at around 58 degrees C so I decided to see if I could test the temp sensor that goes to the ECU.

It was quite easy to get out but as I gently tried to unplug the black with the pink wire broke at its plug. I was not putting any real force on the pink plug. The break point is corroded. Now as these I think measure resistance at different temps and report this back to the ECU I am wondering if this bad joint could have been messing with the resistance.

Here is a pic of the broken wire on the part.

What do others think

Yep agree, it's got to be likely that was your issue

 

[Seastoke]

Check all other bullet cone tions

 

[Bigplumbs]

Check all other bullet cone tions

Easier said than done that

 

[Binnacle]

Easier said than done that

If you can't do it, then get an engineering professional in.