Yamaha 130 2-stroke Rev limiting / precision mix

I recently bought a used (late 90's model) Yamaha 130 2-stroke. It didn't have the external auxiliary oil tank for the precision-mix system. I delivered the boat (ca. 100NM) by stopping and topping up the tank in the powerhead, and the engine ran fine the entire way.

Since then I have obtained an auxiliary tank, but now the RPM's are limited to 2,000 (as if the main tank were running low on oil) regarless of the fill level in the main (powerhead) tank. I have tried both cleaning the float-switch and disconnencting the float-switch, yet the RPM's are still limited.

What other problems should I look for? The boat is located far away from any knowledgeable Yamaha service technicians

[boats.net]

Low oil and Overheat will cause to go into rpm reduction and sound warning buzzer. If don't hear the buzzer, it could be a problem with buzzer or a engine running problem(not running on all cylinders).