Excessively skidding the rear tire can cause a flat. A new tire and tube will be required. Mosquito drum brake is ineffective. The rear brake is easily adjusted with the brass screw by the rear wheel. Twist clockwise to tighten.
Engine smokes excessively.
Using synthetic oil at 40-1 is also helpful. If the engine operates too long with the mixture too rich, the plug will be fouled and the exhaust could become plugged. Pullstarter is broken. Installing a new pull starter is simple and inexpensive, but also avoidable. Unscrew the broken one and remove.