Moped Army

'77 puch maxi sport, biturbo, 15mm bing. I had a 12mm bing on and was hitting 30mph. Went to a 15mm bing because I was told it would help the pipe breath even more and I had one sitting around for my project bike. No change in mph! Gearing 14x45. Went to 15T sprocket and of course my low end was a dog. What do I need to do to gain the extra speed I want so badly?

Thanks