Hi and welcome to Just answer.
Initially, try to check ring under the rotary valve cover. It was causing the ECU to dump too much fuel and choke it out also allowing air to be sucked in.
Another thing need to check is mag cylinder. If it is one that only idles on the mag cylinder you might have a clogged injector. Try switching them and see if it helps. RFI's are known to have problems with the voltage regulators too.
Hope this information will be helpful.
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What do you mean by the ring? Is there an o ring or a gasket under there? Is it between the rotary valve and the cover, or behind the valve?
Yes there is O ring under the valve between the cover.
Also check other thing I mentioned above.