by Adam_Winstone » Sat Aug 27, 2022 8:02 pm
The early mushroom baffle-type exhausts suck!!!
As it reports in one of the period texts, the British market was initially very disappointed by the performance of Jet 200s, much of the performance loss being identified as resulting from the fitment of the earlier type exhausts. I can confirm just how restrictive these are, having real world (very, very obvious) experience of how these limit the rev range of any of the layer spec standard models.
I took a test ride on a pal's totally standard SX150, with the owner being proud as anything of his immaculate machine, only to get just beyond the end of my road before having to turn back to tell him that he obviously had the wrong free-range / gas flow limiting mushrooms baffle type exhaust fitted. Firstly, he was extremely doubtful as he had paid good money for an Innocenti stamped pipe specifically for an SX150, and from a 'respected' (more so in years past) resto expert. However, after showing him the section in the 60s tuning manual about modification to the later spec, he agreed to at least go home and look in the throat of this expensive new box.
Sure enough, mushroom baffle type and 100% wrong for an SX150! He then carried out the modification and called me back a while later to say that it had totally transformed the ride, for the better! We, in my club, still commented that his bike was ridiculously quiet, even after the modification.
I'd not fit a mushroom baffle bike to strangle as LI125S or any of the other late models... in the same way that Innocenti didn't. The further extended port durations of a GT kit give even more reason why not to fit such an exhaust.
The later spec S3/GP pipes are a completely different kettle of fish, extending the rev range enough to work correctly with the lower gearing of these models.