When the needle of a fuel pressure test gauge bounces violently while the motorcycle is running poorly, stalling, and backfiring, it could indicate a problem with the fuel delivery system. Here are a few possible explanations for the symptoms you described:
Fuel pressure regulator issue: The fuel pressure regulator regulates the fuel pressure to ensure it remains consistent. If the regulator is faulty or clogged, it may cause the fuel pressure to fluctuate, leading to the bouncing needle on the gauge and improper fuel delivery to the engine.
Clogged fuel injectors: If the fuel injectors are clogged or dirty, they may not deliver a consistent and steady flow of fuel. This can cause fuel pressure fluctuations, leading to erratic engine performance, stalling, and backfiring.
Vacuum leak: A vacuum leak can disrupt the air-fuel mixture, affecting the engine's performance. It can cause inconsistent fuel delivery, leading to bouncing fuel pressure and the symptoms you mentioned.
Ignition system problems: Faulty spark plugs, ignition coils, or ignition timing issues can also result in poor engine performance, stalling, and backfiring. While not directly related to the fuel pressure gauge, these issues can contribute to the overall problem.
To resolve the issue, you may need to perform further troubleshooting or consult a professional motorcycle mechanic. They can use specialized tools and diagnostics to pinpoint the exact cause of the problem and recommend the appropriate repairs or adjustments needed to restore your motorcycle's performance.