Sounds nice. I am going to have to try that Pine Sol. I noticed you were turning the slow speed adjust counter-clockwise (enriching it). I would let it warm up for a couple of minutes and then bring it to as slow of idle as you can. Then turn that dial clockwise 1/8 of a turn (more lean). Give the motor 10 seconds to respond. If the idle increases, slow it down and turn the dial 1/8 turn more. Keep doing this until the motor coughs and wants to stall or does stall. Then turn that needle 1/4 turn counter-clockwise and leave it alone. You can remove the knob and then reinstall the knob with it pointed down, in the middle and you should never have to touch it again. Your carb would then be set perfectly. providing the proper fuel to air ratio.

One reminder on starting the motor. You tend to grab the starter and just quickly pull it. You want to pull slowly at first until the starter pawl (plastic black gear that grabs the flywheel) rises up and engages the flywheel and then pull as hard as you can. If you pull really hard BEFORE the pawl engages the flywheel you will start to wear down those teeth on that plastic starter and the motor will get more and more difficult to start.

I can’t say what your brother in-laws motor needs but very rarely do they ever complain after a carb cleaning. You’re an expert at that now so give it a 72 hour soak and lots of compressed air and see if things improve. Afterwards the carb needle is set the same way as yours is as outlined above. Just so you know the spark plugs are different for that motor then the one you have. It likes the Champion plugs because it uses a CDI ignition system as opposed to the points and condensers in your motor. The plugs for the 1981 15 Hp are Champion QL77JC4.

I believe I read that the fuel tank should be no lower than 20" below the carb. I would suppose that to be exact ,that the bottom of the fuel pickup tube should be no more than 20" below the fuel pump.