all ideas greatly welcomed. went out on wd M20 last sunday, lovely. new petrol in then. Started fine today after a bit it started running with less power, coughing, stopped and banging. it did this for about 15 - 20 minutes so i was nursing it home, worried i'd be lumbered. Then it just stopped and was its normal self. please have you got any ideas or suggestions?

Your advance cable slackened off.Or points gap non existent.

If it has returned to normal condition / performance without you doing anything to it then maybe it could have been crud in the fuel. Dirt stopping the float needle from seating would flood the carb and cause problems, whether severe enough for your symptoms I don't know. Then it can cure itself as the dirt becomes dislodged (vibrations perhaps ).
Do you have a filter in the fuel line?
Or perhaps the carb overheating and boiling off Petrol? Did it get better after cooling down?
Good luck

Cheers
Pete

email (option): petercomley@web.de

Many thanks for this Douglas, I will follow up these two. what I couldn't understand was how it changed back to normal. all best for now peter

Many thanks for this Douglas, I will follow up these two. what I couldn't understand was how it changed back to normal. all best for now peter

Dear Pete many thanks for this. i don't think there's a problem with carb overheating, never have done before and i have a good spacer between carb and cylinder. no i don't have a filter in the fuel line. It's a metal fuel line so don't know how i could do this. sounds sensible though. good to have another inquiry to try. thanks and all best peter

Peter it is more usual that the fuel taps have gauze filters inside the tank. It wouldn't be a bad idea to drain your tank and check/clean them. Ron

email (option): ronpier@talk21.com

thanks Ron, yes mine has got gauze filters. something to attend to. all best for now with thanks peter