I just purchased a 1997 Sport 400. The guy I purchased it from has rebuilt the top end and replaced all seals and bearings in the bottom end. He was having a hard time trying to get it running. It would start but as soon as you pushed the throttle it would backfire HARD and die.

Now since I have gotten it I have replaced the battery, spark plug and the fuel. When i pull the spark plug out to test for a spark I can only get a good blue spark when using the pull start, if I use the electric start it will give off a few weak sparks then no spark at all. Any ideas on what would cause this? I have yet to even get this thing started.

I'm kind of a noob when it comes to tesing electrical things. so any insight you have would be much appreciated.
Thanks