iv only got the downpipe on at the moment will that affect anything because when im driving at low rpm it kangaroos a bit then cuts out when i stop at lights or a junction, i had this same problem with a bmw i used to have that turned out to be a hole in a intake pipe

What's the idle like ?

What sort of fuel system are you using?
Where's the pickup?
what size pipe?
what type of pump?

ok, slightly lumpy. erm im not sure the answers of an of those questions, i just had a new crank sensor do you think they could have put it in wrong cauing these problems or something along those lines

Was it ok before you had the work done?

i think its the hg thats gone im getting water out the exhaust and when i rev it loads of bubbles in the radiator

Ohh, doesn't sound good.

Ways to prove it:

1)Have a look for milky residue in the oil filler . Chances are it's gone between a combustion chamber and waterway though so you might not see anything

2) Have the plugs out and look for dodgy colours/water deposits. You can also spin the engine over with no plugs is and see if water flies out

3)get a compression test done.

got some milky residue on the filler cap and a small puddle out the back of the exhaust and i took the rad cap off sand revved it and there was loads of bubbles

Yep sounds like BHGF. It's not too bad on these, but you'll need to go to a machine shop and get the head skimmed as they're alloy before you put a new gasket down.

will it be ok to skim again as it was skimmed last year

As far as I understand it, skimming alleviates slight warping by making the surface flat again? So unless it's warped in exactly the same way, different bits will be cut.

Basically I don't think you've got a choice, you may as well try.

i see what you mean