Lean (PING)

[IOPort51]

CK the base area on your carb. They are well known for vacuum leaks that will cause a lean fuel mix. A lean mix can lead to 'pinging'.
Use VERY soapy water for this ck, and see if the bubbles get pulled inside.
Also make sure ALL of your manifold bolts are tight. Use the soapy water here too.
LG

I have always used carb cleaner or even gas in a spray bottle. I know, it sounds dangerous and it may be, so be careful.

engine will speed up when a leak is found and the flammable liquid is drawn into the manifold.

 

[Torxhead]

Another item that can cause your engine to ping are carbon deposits in the combustion chamber. A good gas additive like
bk44 is one way to clean it out along with mashing down on the throttle once in a while.