The 1B was the 20 MPH engine, so it'd be doing what it's supposed to if it weren't kitted. If you look at the attached picture, the stock head is on the left. Note that the 70cc head has extra fins, depending on which kit is supposedly on the bike, the fins may look different, but all of the 70cc kits have extra fins over the stock jug. Bottom line is that if your jug looks like the one on the left, you have no kit.
If it does have the kit, how's it running (other than slow)? If it's not running smooth, check the usual stuff like the plug, points, carb, exhaust. If it is running smooth, it may just need a larger carb/intake and exhaust. The kit by itself won't necessarily give you an increase in top speed, you might (probably) will have to help the engine breathe a little better. If you remove the airbox or the exhaust and the bike runs faster, there's your answer. If you're going to leave any of that stuff off the bike for more than a brief test, you'll need to re-jet the carb or risk damaging the engine.
Good luck and have fun.