Make sure that the ignitor is well grounded. It grounds through the body of the ignitor so when you mount it, its being grounded. I use a small wire wheel on a drill and clean the metal on BOTH surfaced really well and then tighten up to the inner fender or such.
I have also seen where the wire on the ignitor plug are loose in the plug itself.
You should have heavy gauge grounds from battery to motor, motor to frame and motor to body. I used 4ga but that is probably overkill.