Frustrating Yamaha 50 hp 2 Stroke Problem, help!

[Zcarpman]

It does sound like it's backfiring through exhaust. I have the service manual but I cannot find the link and sync procedure. I think that is the issue.

 

[Zcarpman]

So i took it out the other day on the lake and ran it through a bunch of tests. Up to 1/2 throttle (10-12kts) on my Carolina skiff the engine sounds and pushes great. Once you start to get close to 3/4 throttle it starts to skip almostand run poorly. It won’t die at all just skips and doesn’t gain speed. If you pump the ball it doesn’t help at all. If you restrict airflow to the carbs it will die so the mix seems alright. One thing I did start to mess with is the mix screw on the top of all three carbs. These definitely effected the overall performance. It seemed every time I tried different settings it would run differently. I got it up to 16 kts and running a bit better by screwing the screw outwArd. Any ideas at all? I’m thinking maybe it’s a timing issue. Is the CDI marking “II” supposed to be lined up for full throttle ?? If so, it is not currently it hits the stopper at about 1/2 throttle. Maybe it’s a timing issue. Anyways attached is a video of the skipping. Any help would be great , going to pop the carbs off and go through again tomorrow. Maybe the reeds ??

heres the video:
https://drive.google.com/open?id=1gn3Py7GCNs-Sdfl8SI2Ehu5k1Ebk0_4_

 

[lerobert]

did you re-build the fuel pump for the prime start assembly? did you test the electrothermal valve on same? have you tried switching the system off manually? weird things can happen with that system. easiest test would be start it up normally let it idle for 5 minutes then turn red lever on middle carb all the way down to the off position then see if it runs right.