That gas tank needs to be up on the top bar there for the fuel to flow downhill...If you notice, the fuel line goes down and then has to come back up to the carby, that will probably result in inconsistent fuel feed as these things do not have fuel pumps but are gravity feed, meaning it could starve for fuel, and therefore proper lubrication of the moving parts from an adequate oil/fuel mix as well as sputtering out on you and inconsistent running of the motor.
Also the fuel filter is on upside down, there will be an arrow on that filter and it is supposed to be pointing to the carby...The bottom of the exhaust, as blackened as it is, kind of confirms all of my observations already listed above...thanks for the pic which is quite helpful...DAMIEN
Ps...In order to place the tank on that top bar, those cables on the bar will either need to be re-routed or you will have to devise some sort of fixture to "tunnel" those cables so as not to be bound up with the tank directly on top of them...Whoever built it did not think things out correctly, but is easily correctable...DAMIEN
Ps...You will need to remove a link or two from the drive chain as well...it is way too loose.