So here's the background story. I recently acquired a 1984 Evinrude 9.9hp outboard model: E10BALCRA, AC Lighting rope start. It started well when tested but then would not start after purchase and i took it into shop where they charged me for a couple hours work to fix what they said was an electrical problem (was told some wires were loose under the fly wheel and were shorting out the motor).
So the shop got it starting for me and i took it out for a run on my 14 ft alum fishing boat. The motor ran well initially with the exception of acceleration not being so smooth on the throttle (throttle hesitation?) - motor would not power at same rate of throttle being turned, and you had to full throttle it to get it going and then could decelerate to less than full throttle.
Anyhow, so it ran well for about 5-6 hours of maneuvering about at various throttle speeds and with multiple breaks for fishing. Then I had to run it in full throttle in reverse (not sure if related to problem) to avoid collision with a barge coming around an island, and have been having the following problem since:
The problem started to present like the engine was running out of gas, sputtering and losing power (had plenty gas). When at full throttle the motor would just slow down and run at about half power. It would go between running at half power for a few minutes to back up at full power without having changed the throttle. Kind of felt like the engine was getting overheated or it was not getting fuel. Sometimes it helped to turn it off for a few minutes and let it cool off, but eventually before making it back to the ramp, it only would run at half power. I tried taking it back on the water again and it will still run but at about half the power that i know it is capable of.
I was lucky to be able to take a couple video clips and are attaching two videos to show engine running. Both are at full throttle, one when running well and the other when experiencing the above mentioned decreased power. You will be able to see and hear (sputtering) the difference in how the engine runs. Just want it running well again.
Please advise and help me diagnose the problem. I really can't afford to take it back to the shop again. Thanks for your help.