You should check the functioning of the power valve plunger which is fitted to the air horn. A bit of light oil around the shaft helps to smooth the operation. To check its operation I use a little 4mm joiner and some dripper hose from the hardware shop and simply insert that in the port and suck on it to see that the piston action is okay. I would do that first before shelling out $300.

Also, it is a good idea to remove the power valve itself and blow it out to ensure there is no debris in it causing it to leak.

How clean is the bowl ?

I usually clean all of the crud out with some caustic soda . Immerse for a few minutes only and rinse well. That caustic soda is powerful stuff. Watch your eyes and hands as it will burn. Take care.

Also the fact there is smoke from the exhaust is concerning . What colour is it ? If running rich then I would expect black smoke . If it is blue then that is oil and you have another problem , most likely rings or valves.

Have a good look at the PCV valve to ensure that is not blocked or jammed and that the hose is not split.If the PCV valve is open all the time it will run like crap and blow smoke because of the oil it draws up from the crankcase.