I finally got around to sorting this out.

I had a good look at the wire going to the condenser and noticed that it was a little low on smoke. I think I may have cooked it when fitting a non-working tacho a little while ago.

I obtained an old condenser off a mate today and chucked that in and it'll rev straight up to 7,000 and beyond.

I'll be putting in an electronic system shortly so this'll do for now.

Cheers,
Simon