ive got it working it revs up fine but on tick over it sitting at say 900rpm but every few seconds it flicks up to about 1200rpm , by that i mean it just shoots from 900rpm to 1200 rpm and then back instantly and does that every few seconds when reving up its fine

any idea's?

ive also read about the diode thing , you have to put a diode on each of the negatives off the coil and them connect them together to go in to one signal wire , is this correct or have i got it wrong??