yes thats the piont to find the 1 that can not jump as far... ie ciol 1 can spark 3 cm befor missing, coil 2 can spark 2.7 cm befoe missing ciol 3 can spark 3 cm before missing and coil 4 can only spark 1 cm befor missing,,,, ciol 4 is weak and faulty. under load/ stress the coil cannot handle the load it is being given. and under revs ect or hill clime this will cause a miss. as in i belive a direct relation to this the amount of voltage this coil is able to produce is the distance it can jump before missing..
its also under ability of the plug or lead as if a lead has high resistance or an open circut. it can cuse a miss, poor isulation on the plug or surverly fould plugs, the k100 has a tube on the end of the leads? yes these are comon leak spots on cars, as the revs increese the voltage from the coil increases makeing the spark able to jump further, this enable it to jump threw a verry small split or imperfection in the tube bypassing the plug and earthing on the rocker cover or head out side the head. easy way to check for spark leaks, at night with the cover off and rev her to til she misses and look down each the hole to see if theres any blue/yellow flashes. but u can usally hear the tick tick tick...,.
but the spark miss to me is eliminated buy the pig root and back fire, which says to me either the spark has built up in the lead or ciol due to hi resistance and the let loose buy over coming the resistance. the only other way i know u get a back fire is hot raw fuel entering the exhaust and coming in contact with fresh cold air. . but no mention of an exhaust leak. so the hes has been replaced ( hall effect sensor ) for clarity, no ehaust leaks for back fires,the fi ecu replaced, assuming the mech did his jobproper and chacked the pump is able to produce enuogh flow, the injector have beeen replaced.. the miss has to be spark and sound typical of a coil or ht lead or ignition module
there is the possibilty of a lean backfire, can something shut the pump down for a sec or the injectors... have each of the injectors been tested while running with a led test light. just watch the flashes to see if 1 goes out of sync or stops. or just goes stupid in its flashes, u need to chack 1 at a time and rev the bike up slowly, the test probe needs to be in 1 wire or the injector plug and the earth clip, attach it to a paper clip and probe the same injectors other wire, u need to probe both wires or it wont flash.
so in breife get the fuel pressure east and flow test again..
check for a weak coil, or bad lead,
test each injector pulse,, will also i am assuming in 99% of automotive industry chack the pulses to the coil to.
sorry it massive post .