DF60 2001 do not rev up

[Sarrre]

Hi,

I installed a used Suzuki DF60 2001 with 300 hours on a friends boat. This engine had some water in engine oil and we found out that the gasket for the intake manifold was leaking, so we put a new gasket and no water in engine oil so far.
After installing this engine on the boat, we had some trouble with the original remote control box. The engine would not go down to idle after increasing the throttle. We found out that the remote control did not pull the throttle wire all the way back, so we change it to a brand new remote control and solved that problem.
So, after putting the boat in the water we can not get the engine running above 3200-3400 rpm. The compression is fine. I don't remember the numbers, but it was even on all cylinders, so I don't think it is any issues there.
Even if it is wrong propeller pitch, it should rev up more right?
Could it be something with the new remote control box that is not compatible with this older engine?
I first suspected the neutral switch was activated also in gear, but I think it should limit the rpm by 2800 then right?
Any other suggestions?

[Moonlighter]

Neutral throttle switch on the engine will limit revs to about 3000rpm if it does not detect the engine being in gear - so that is the first place to look.

If that switch is stuck, broken or misaligned the ecu will not see the signal that the engine is now in gear and will restrict spark, advance and fuel supply.

[Sarrre]

Yesterday I was out with the boat all alone. With the lighter load it was able to reach above 4000 rpm. So it should not be the neutral switch at all. This time I also noticed that the rpm decreased and increased back and forth between 3400 and 4200 when pressing the throttle at the bottom. I also tried with another portable tank with the same result.

We took of the injectors and they looked just fine. Could it be injector problem anyway? Any other suggestions? I ordered new spark plugs and will do a new test tomorrow. I will also put some injector cleaner in the portable tank before the next ride....

[Moonlighter]

Have you verified that the throttle on the engine is fully opening when the throttle lever on the controls is pushed forward? It could just be a cable adjustment or a problem with the control box you are using.

Also, there is a small mesh filter inside the VST - if there has been dirty fuel at some stage that can get partly clogged and cause surging etc. Its really important on these engines to run an inline water separating fuel filter between primer bulb and the engine to ensure a clean fuel supply.