350 Sloper cylinder base shim

[Sigarus]

Hullo All,

I've just found this forum although I have owned my L29 OHV Sloper for over 25 years and have had it running for 5 years. I have a few other 'classics' and don't often ride the Sloper, in part because it is quite slow and so isn't much fun if there's much traffic around. I've put a few miles on it recently and have been pondering why it lacks performance. From some of the posts on here it seems I'm not alone in this.

I have a specific question about the cylinder base 'shim', part 24-384 I think, which raises the barrel a little and so reduces compression. The same part is common to the 350 and 500 Slopers despite the difference in bore size. Has anyone here investigated the effect of this shim/plate on performance? Is it an 'optional' part which can be omitted without causing the piston and valves to come into contact and does leaving it out give a useful improvement in performance by raising the CR ?

BTW, ignition timing, carb settings etc on my Sloper are as per the manual. It is fitted with an AMAC 15MDY carb which has been refurbed by Martin Bratby and I think is the original.

Thanks in advance for any information about the shim.

[Sigarus]

I've found the answer to my question in a 1930 BSA manual, just in case anyone else is interested.