I found this out the hard way...after buying some new A35 ignitions I noticed they didn't behave like original one's even though they had the same part #...instead of retarding 5 degrees like Lee said they would spark every other rotation and bike would hit a wall...that felt like a pipe/carb problem...very sinister...any puch runnin a tomos ignition must be timed with a strobe light and revved up to peak rpm to verify which ignition and degree your set too ...hope this helps