Today I have tried to solve the dust issue by using some pipes to draw air from the front of the bike to the air intake. The problem is there isn’t enough space to fit a large enough pipe to supply sufficient air to the sucker. A basic bit of maths suggests it wants around 40L/second at redline if the cylinder is filled 100% in each stroke. So its easy to understand why three 25mm tubes to the front of the bike was not enough. The bike ran at lower revs but when accelerating moderately it would become very rich due to a lack of air.
Righto, rip all that out.
I went back to a more elaborate version of what Donnie had suggested. Basically using duct tape to stop it drawing from near the back wheel. With rags, duct tape and filter foam I carefully redirected the intake forward.
We will see how it works tomorrow.