Another idea would be to replace the ignition with a RCXL igntion. I got one from CH when the igntion on my 3w-50i went bad. They sell a universal sensor kit that attaches via a hose clamp. Looks a bit crude but works very well. I've had two of these engines and although I have not run them much, both ignitions went bad, both fixed under warranty. The RCXL ignition has my vote, even if only because it can operate with 4.8volts instead of 6. You are using a good 6 volt battery, right?
Sam