Hello iwould like to lower revs by 1000at say 70mph what sprockets do i need

You will need either a larger transmission sprocket or a smaller wheel sprocket. The larger percentage change will occur with an increase in the front sprocket number of teeth. The way to mathematically determine that is to consider the present tooth ratio/RPM and relate that to the desired ratio. There are practical limits on how big the front sprocket can get before having interference problems. A 2-tooth increase should come fairly close. It would take about 4 to 6-tooth decrease in the rear sprocket to achieve the same results. Take your pick--the front sprocket should be cheaper and much easier to install. You will need to adjust the chain length accordingly. There will be a minor acceleration decrease due to the change. A fatter rear tire will also increase speed somewhat too. Hope this helps!