If I don't start the bike for about a week I need to clean the front plug before it runs cleanly. The fuel tap is always turned off before leaving it.

Could this be a worn needle? Any other suggestions?

After cleaning the plug it idles and runs fine.

Possibly, or simply a little dirt is preventing it from seating properly.

Whip off the carbs and give them a good clean.
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Hi , also check that your fuel tap is closing properly . Pull the hose off and check if there is fuel dripping from the tap . This can also contribute to your bike flooding the front cylinder .