1990 fatboy seems to be droping to one cylinder and backfiring violently, what am i looking to check, fuel or ignition or both. regards

Jeff Broom, May 2014

go for the ignition(spark) of the plug you can get a tester that fits the plug and you put plug lead on that run it and watch for spark in tester window. If intermittent first change the plug lead. If you see a black line down the plug then change the plug. The other point it could be head gasket losing compression so neat fuel goes into hot exhaust and goes Pop bang pop BANG. as you know. So trial an error. spark, lead, gasket although latter unlikely. add cleaning fuel jets & filters. Did all on my BSA 500 several years back(more than I care to remember) and it worked fine. Good luck always wanted a old style Harley never had the cash.

Bob UK, May 2014

is this during normal riding or on the over-run? have you tried new sparkplugs? i assume you know which cylinder thats misfiring? could be that, worth trying first, backfiring could be an upset in the fuel/air mix caused by an air leak between the carb and head or aftermarket exhaust pipes where un-burnt fuel is igniting in the pipes.

perry, May 2014