@Florian Rädler
Hey man! thanks for posting a great question!
Alright first off heres a list of lean vs rich conditions that will definitely help you in the tuning process and help guide you in the right direction so you're not just throwing money at the bike hoping it fixes itself.
Lean Mixture Symptoms -
1 - It is difficult to apply the throttle quickly or the engine picks up speed when the throttle is rolled off.
2 - The engine knocks or Pings or overheats.
3 - The engine surges or hunts for a stable RPM while cruising at part throttle.
4 - Engine acceleration is flat or slow to pick up.
5 - When the pilot circuit is too lean, there will be popping or spitting in the carburetor as the throttle is opened. Sometimes there will be popping or after fire in the exhaust on deceleration after the throttle has been closed.
6 - Engine performance improves in warmer weather, or runs poorly in cold weather.
7- Engine performance worsens when intake is removed.
8 - Baked white and flaky spark plugs.
Rich Mixture Symptoms -
1 - Engine acceleration is flat, uneven, not crisp.
2 - The throttle needs to be opened continuously to maintain consistent acceleration.
3 - The engine performs poorly when the weather gets warmer, or the engine works better in cold conditions.
4 - Black smoke coming out of the exhaust.
5 - Poor fuel economy.
6 - Engine performance improves when the intake is removed.
7 - When the pilot circuit is rich, the engine will idle roughly, or not return to idle without blipping the throttle, the exhaust can smell of excessive fuel and burn the eyes.
8 - Black sooty or fouled spark plugs, black and sooty exhaust tail pipes.
all that being said, you didn't mention whether you have replaced the intake boots or not. You also didn't mention if you actually tuned the bike or just slapped some jets in there LOL! Ya do need to tune and check the spark plugs to help determine whether you are running rich or lean, however before you can even do that, You really do need to replace the intake boots or you're chasing your tail. It sounds to me like you have a nice vacuum leak and its very likely coming from those intake boots. especially if they’re the originals. as the rubber gets older its way too hard to effectively create a seal anymore.
