T H E O L D G R E E N B E E M E R
RIDING A 1974 BMW R90/6 FLAT TWIN
OPENING UP THE EXHAUST MUFFLERS
If you are looking for a way to let your R/? bike produce a bit more punch from the
pipes then there is no need to shop for new mufflers. Make or get yourself a drill
bit extensioner and do the following. First drill a small pilot hole in the plate at
the end of the conical ( megaphone ) section of the muffler. Enlarge the hole
up to the point you are satisfied with the sound, I went as far as 16mm and
additionally drilled an extra 8mm hole at the end of the reversed cone at
the end of the muffler, opposite the condensation vent hole. This gave
me the punch I was looking for, strong not loud, acceptable by other
roadusers and the neighbours in my street but a lot more powerful.
Drill the separation plate at the end of the megaphone ( 16 mm ? ) and / or drill
an extra hole opposite the condensation ventilation hole. I drilled the separa
tion plate with the mufflers still mounted on the bike with the help of a drill
extension tool. This way I was able to take the bike to the road in
between drill sessions to see / hear what would happen next.
A bit more punch from the pipes but still decent enough. Carburettor jetting was
left as it was. Opened up the idle screw settings slightly ( richer ). Drove
many years since, spark plugs look perfect ( coffee ).
To keep these silencers alive for a loooooong time, remove 'm from the bike
fill the inside with boiled linseed oil, shake, roll, make sure the stuff goes
everywhere and drain the excess back out. Leave 'm standing upright
for a few weeks, the longer te better, to dry on the inside. Don't forget
to clean the outside as backed in linseed oil is hard to remove.
Repeated every few years these pipes will serve you forever.
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