i'm not sure why, but the jbm industries diaphragms i used on my 87 vt1100c both tore after a very short time. i have replaced them with the stock oem slides and diaphragms off my 98 spirit (hich is now under a severe overhaul). i've done a couple or diaphragm replacements and never a problem. any ideas? while i was doing the rubbers i also put in the dynajet jets and needles from the 98, the 87 ran like a banshee. however my mileage dropped to the mid 30' so i took her down again and put 165's and 142's in along with an ignitec cdi. well, not nearly the top end or high rpm power that i had with the dynajets. during the last trial run today, i also changed out the ignitec cdi with the stock box and it did perform a bit better, telling me that ignitec (the non-adjustable model) does not perform as well as the stock. i'm sure their adjustable box would, of course, run as hot as you adjust it to run. i run a k&n and have removed my baffles. originally it had 155's and 142's with one washer (shim). the configuration i now have is the one recommended by the jet companies chart. so i see that if i want to haul azz and don't care about the mpg's to go with dynajets kit. the tapered needles and their larger jets DO make a big difference. i remain bewildered by the failure of BOTH of the jbm rubbers??