You can modify these easily and cheaply folks, as an ex electronics guy i have found the fix, the problem with most 500, 650 and some others is that the CDI box has a rev limiter, you can order a CDI through jaycar electronics $50 AUD, or you can order a high performance CDI off ebay.
The CDI off jaycar works like a dream, beware though the main diode coming off the charge coil may blow so replace with a 40volt 3 amp schotsky diode parallel with the 5804 diode.
Be warned though, this thing now flies but you need to limit the revs otherwise your head will blow.
P.S, if anyone has a problem with the coil you can buy a second hand coil for the new cars, these coils are one but have outputs for two spark leads and should read about 3-5 ohms, connect to the ground and orange wire off the CDI, it does not matter which way on these, the older ignition coils have a ground and positive, the park plug gap is 0.24"-0.31".
Last edited by viper000; 12-31-2012 at 12:59 AM.
Reason: plug gap ammended