if gapped slightly wrong will cause misfires, probably 10-20/1000 rpm or so and/or maybe hard starts,or/and power loss, gapped more wrong, more hard starts and more misfires, etc. etc. till it just wont start or restart or run like crap....dwell time, preignition, detonation, blah blah blah... gap them to spec and if you have to make a choice then round up, but too much can cause the above....