Effective troubleshooting can be simple and rewarding if you stay on track and don't jump around from system to system.
Start with a simple system like fuel delivery, from the tank to the intake manifold, fresh fuel is needed and can be visually verified.
Then move to another system and follow that system from start to finish, don't assume, and don't wander from system to system. check it and rule it out as the culprit before jumping to another conclusion.
Air/Fuel/Ignition/Timing = combustion

Best Regards
Will