A popping sound is not a normal occurrence with a Power Flow System. The following list should help you troubleshoot the problem:
1. Is there evidence of ‘blow by’ (exhaust leakage) where the tailpipe slides over the 4-to-1 collector or around any of the headers? If so it may be cause.
2. Check the muffler insert located in the tail pipe to be sure there is no partial or complete blockage.
3. Check your induction system for any leaks.
4. Are you leaning as much as the Power Flow will allow on the ground? The Power Flow will enrich the mixture so more aggressive leaning is needed during ground operations.
5. Check the idle mixture on the carburetor by doing a Lycoming idle rise. If it is set too rich it can lead to excess unburned fuel which is ignited by the hot exhaust pipes.
In addition to the above, a leaking primer can cause popping in the exhaust at low power settings. Simply block the line and test fly.