i have a single weber on an 1800 bay window with extractors. i can't seem to get rid of a slight popping coming from the exhaust. not quite a backfire but more of a pop when ideling no holes in exhaust. just got a new head aswel and the popping disapeared for about 600klm's and then returned. valves are still set OK. ???

If it is spitting/snapping out the carb then it is lean

If it is popping out the exhaust then it is rich

Take the air filter off and watch carefully

My guess would be a blocked idle jet.

You say a single Weber. Do you know if it is a progressive or an IDF???

Either way go to http://www.redlineweber.com  and look at the pictures there to see where the jets are

Take em out and blow or compressed air through them