Surging Yamaha 60hp 2 stroke outboard motor

Yamaha 2 stroke 60hp outboard motor surging.
I might not be a qualified outboard mechanic, but resolving engine problems i enjoy.
so my friend informed me that when he ran his boat on wide open throttle it would be as if the motor was missing.
so it must be noted that the owner diagnostic was incorrect and as such widened the fault search.
we started off by doing basic tests on the 2x motors.
we checked both motors compression which measured between 90 and 105 psi.
to many this would be, low compression, but being 1640 meters above mean sea level, the readings were actually good.
so we knew, all cylinder compressions were good.
all spark plugs were new and not fouled.
we also set the carbs "synchronizing"
the mixture screws were checked and found to be completely out on the one motor "port side motor".
the top carb screw was completely closed, the middle carb screw was to far out and the bottom carb was also to far in.
the other motor carb settings were again on a base line of 1,5 turns out.
so we set all carbs to 1,5 turns out.
the engines were started and idling was set to around 1100 to 1200 rpm.
if rpm is set to low, the motor can stop running when placed in the water.
the engines were run and all seemed good, no misfiring or any faults present.
The boat was then taken to the dam to do a water test.
in the water all goes good, idling is perfect, etc.
we start running the boat after warming the engines and all seems fine.
on a stretch of 600 meters the problem started showing up around 450 meters into the stretch.
the starboard side motor started surging where it will loose power and then regain power but loose power again.
so it was already clear that a fuel delivery problem was present on the motor.
it was decided to remove the motor cowling and carburetor air filter.
this allowed one to look directly into the carburetor to see fuel delivery into the cylinder.
the stop start allowed the fuel bowl to fill up with fuel and as previously one needed to run the motor in WOT for quite some time before the fault returned.
with the fault returning and watching the fuel supply closely it was clear that the bottom carburetor was running dry/ or a fuel delivery to the carb was present. a slow motion video was taken to show how the fuel delivery to the cylinder stopped at times.
the boat was taken off the water and the carbs were stripped off the engine.
the carburetor was dissembled by removing the needle and seat as well.
only when air was blowed into the fuel supply hole could one feel that a obstruction was present. the needle and seat jet was then removed and it was found to be obstructed. a wire was used to clean the jet out.
it was fitted back into the carburetor and the air through the jet was now much better.
the top carb was also dissembled and the air through both passages seemed to be consistent now.
the carbs were fitted back onto the motor.
the boat was tested and found to be running smooth without any further faults or problems present.,
it was a fun exercise and i'm glad it was resolved.
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