Motorcycle Questions? Ask a Mechanic.
Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, doubtful if it would be a timing chain issue.
And if fuel quality has been ruled out, then the other possibility would be fuel delivery (least likely) and/or electrical/ignition (most likely).
Preliminary checks (if have not been done) would be on the sparkplug burn color for a potential lean mix condition and/or an air leak. Along the same line, ensure that the air box + filter (element) are correctly installed/mounted and air is allowed to pass through the designated air entry slot.
Similarly determine if there is sufficient fuel inside the carb bowl.
Proposed further checks (if have not been tried) on the possibility of over/under-voltage, regulator/rectifier and/or stator issue. With a volt/multi-meter, determine the battery voltage when:
Please post back results / observations of the above once tried.