Puch Maxi N only accelerates well above 30 km/h?

I bought a Puch Maxi N with an e50 engine. Set up: 15mm Swiing carburetor, 15mm Swiing intake manifold, 38mm Swiing cylinder, 38mm Swiing cylinder head, air filter with rating air strainer, 28mm Cigar exhaust and electric ignition Otherwise everything is original. Up to 30km/h the Puch Maxi has poor acceleration and not much power…