Ihave just replaced the head gasket on my fiat punto TD 60 however?

I have just replaced the head gasket on my fiat punto TD 60 however when i go to start it up, the engine turns but it wont fire up. There is a "phutting" noise coming from the throttle body area and smoke coming from the throttle housing, i have had this problem before and was told by a mechanic that it was the CUB gasket that had blown, ive tried looking this part up on the internet but can find nothing on the spares websites relating to it. I cant afford at the moment to put it in to a garage so will go ahead with the repair myself but as ive said i cant find the part in question, or is it something else causing the problem.