Do Dave silver's still offer GSM systems? My 500 had one fitted when I first had it, the silencer had rotted apparently but the collector and downpipes still had good chrome and were solid, so the previous owner had grafted on another silencer, also chrome. The result was great. The random silencer was from an auto jumble and turned out to be a triumph rocket 3 - 70s one, quite rare. I heard the previous owner bringing it over from about 6 miles away. Power output was good too though it had been fitted with a K&n retaining the phlemnen chamber and was probably 're jetted. Over the years I've fitted cb550 engines, different exhausts, almost all the 4 into 1s around on the used markett, K&n pods but only in that first setup had quite the power output to unstick the rear wheel if thrown into a corner (sidecar so that's more likely and awesome fun) I must say Lazer 4 into 1 was both loud and very tough / brilliant quality, mine was on for quite a few years, used in all weather's, as my only transport, never rusted and it was rather old and dented when I bought it. It also was ok with standard jetting as were my mortad (Neta 4 into 1 and the chrome mortad system ( not so good in durability, the downpipes are still good but the silencer and collector went but again all weather's and bought used. For a custom it's no bad thing to play with fitting alternative silencers to a 4 into 1 system where the silencer has died. Saves money, and you get something different.
