I am having a problem when riding my 1987 tw200, when first started up it seems fine but after riding a few minutes, sometimes longer than others it starts bucking like a bull. Acts a little like not getting gas but believe it is electrical. Carburator has been cleaned and tank is clean. Am looking to replace the black box since I understand that the electronic ignition on early models was sometimes a problem. Does anyone have a used black box (computer) to sell.