My Twin turbo z seems to be running way too rich, at around 5000rpm I lose power then it kicks back in. The exhaust is very fumey, smell definately petrol I would say. Can anyone tell me where to start?

Check for boost leaks

 

http://www.boostpro.net/guidesz32basic.html

http://www.boostpro.net/prodtester.html

 

The boost leak kit is basically a piece of wood/coffee jar lid/whatever you can find that fits the hole then put a tyre valve through and tighten. The equipment shows a pressure gauge fitted to it that's not necessary if you have a garage style tyre pressure gauge. I chucked a smoke pellet in there when I did mine so the smoke pours out of wherever the leak is, only problem with that is if you don't locate it quick enough the engine bay fills with smoke and you can't see anything