I am new to the bike building but wanted to take on a project over winter to keep me busy. I purchased a 1973 cb750 in was not completely put back together but it would at least turn over. I got it home and found out they had the coils routed to the spark plugs backwards. I fixed that and it fired right on up. It backfires when you get it to about 3500 rpms. I thought I was doing great so I then today I fire it up once and now no power to head lights nor will the starter turn over. I am not very good at electrical stuff and need some help. Thanks.