125-200cc detecting pinging on a small bore

On a 250 or bigger I can always hear if the motor is pinging. But I am not sure if it is so easy on a small bore. I have a 144 now and recently had .3mm shaved from the head.

Anyway, I tried pump fuel yesterday and it ran fine but when pulling a hard load with the power vavle shut there is some noise. It shounds like it is coming from the pipe. It sounds like air being sucked through a thin metal pipe. I mixed in a little race gas and did not notice it anymore. Is this a sign of detonation or should I just hear a normal pinging like on a bigger bike?

raise the needle one step, or, go up one on the main. did you get yer squish/chamber reshaped? no pinging is normal and will kill an engine. whats the plug look like? when it starts pinging chop the gas, hit the kill, pull the plug and check it.