The modern Zama RB-K75 (as well as Walbro) are often almost impossible to completely clean due to passages and orifices hidden behind welch plugs.

If you have cleaned it thoroughly and still have problems, replacing the carb may be your only solution. In the web the RB-K75 goes for between $40 on Ebay to as much as $60.

Slightly cheaper would be to get the Rebuild Kit (P005001670 $15 - $20) and the Diaphragm Kit (P005001660 $8 - $10). However, you may still have problems.

ggoyeneche,
Am trying a longer soak and working on circulation behind the welch plugs with a syringe if possible.
Thank you for confirming the problems involved.
coho

Soaked carburetor for several days. Can now start engine but runs rough, does not reach top speed and will not idle (idle speed screw is turned all the way in)
Would it be worth buying new welch plugs and jet How do I remove plugs and jet? Then soak again? Or better off just to get a new one?
Thanks, coho

Are there links to good diagrams or pictures of the carbs internal parts you can share? Or! Have you taken any good pics to share? I usually feel a repair can be made if you have the experience and willing to give the time that a repair shop can not afford.

Give a little history. Such as, could there be some mechanical corrosion, Etc vs varnish/gum matters? Has it been stored with stabil or Etc in the fuel and maintained related to filters, fuel lines, carbon and Etc? When did it run good last?