425 Ignition help

My 425 has intermittent spark on the left side. This happens mostly on start up. Engine runs on one cyl. for 30 to 60 seconds then spark returns and runs good. So far I replaced time delay mod. check and cleaned all grounds and connections switch coils side to side still hit &miss on left side. Deere wants $$$$$ for ignitor. The only other thing I can think of is the pulser coils. I hate to spend the bucks on the wrong parts flying blind. Im only out 20 now on the time control mod. I hope one of you guys can set me straight. Thanks for any help you can throw my way. BILL