If it has a Marvel-Schebler carb it has an acceleration well that supplies extra fuel when the throtle is opened up quickly. Either your float level is low, OR the carb is adjusted too lean, OR you have an air leak around the carb metering system. I"d try turning up the mixture first to see if that helps.acceleration.If it doesn"t, check for an air lleakaround th throttle shaft, the carb to manifold interface, or the manifold to cylinder head/block. Look for rust holes or cracks in the manifold itself. Spraying starting fluid (Carefully because it"s very flamable) around these areas will cause the engine to speed up when you hit the leaky areas.
You"ll also need to check the timing and the advance for functioning as well as the spark(Fat and bluish-white).