My bike came fitted with some very poorly designed stainless downpipes, 4 into 1, huge bore sizes throughout, no balace pipes anywhere, the bike had a bad flatspot between 5-7.5 k rpm, I reduced the pipe size after the collector to approx standard and this helped a lot, the flatspot is now between 5750 rpm and 7250 rpm , I've tried different needle positions and the carbs are spotless. Now for the bonkers bit !! I'm seriously considering reducing the downpipes sizes by squashing/crushing them down to approx the same cross sectional area as a standard pipe. I guess the crushed area will be about 7 inches from the head.
Any comments or advice would be great,