Eigentliche Frage bezog sich auf anderen (offenen) Auspuff mit original Lufi.
Quelle Mikuni:
"Backfires in Exhaust
Note:
It is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid-to-high rpm. In fact, one should expect a well-tuned high performance engine to "pop" and "crackle" when the throttle is closed at high rpm.
The popping is a result of the air/fuel mixture becoming very lean when the throttle is closed and the engine is rotating well above idle speed. It is also necessary that the exhaust system have rather open mufflers.
Why This (normally) Happens:
1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system.
2) The combined effect of the closed throttle and elevated engine rpm is to a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat.
3) Under these conditions the pilot (idle) system cannot deliver enough fuel to a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there.
4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires.
5) Completely stock Harleys do not do this until open-end mufflers, such as the popular Screamin' Eagle slip-ons, are installed. The exhaust must be both free-flowing and have an open exit for the popping to occur."
Immer alles unter der Voraussetzung, dass Zündung stimmt, Ansaugtrakt und Abgasanlage korrekt sind.
Man sollte auch immer bei den Ratschlägen berücksichtigen wer sie macht und ob vielleicht nicht doch das eine oder andere kommerzielle Interesse am Einbau von Steuermodulen und Prüfstandläufen besteht!
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"Men do not quit playing because they grow old - they grow old because they quit playing!" Oliver Wendell Holmes