Mine seems to start to jerk at +180 kph, like it wants to go on but cant? up to that point its pulling well.... that cant be its max can it?
No, and since it has been modified, I would say that like many, the fuel mixture is not right. Many have never been set up properly, which can itself lead to engine damage. A standard 2.2 Murena new could do 200kph (125mph) and mine did just that when it was new. :-) (well you always want to do it once to see if its true don't you!) However, after modifying I have found many are too weak at the top end and cannot do much over around 160-170 kph. This is partly because many twin side draught carbs. supplied in the U.K. came from a company that doesn't seem to know much about tuning in my experience. I have not seen one car from them or engine modified by them that has been right.
There can be a number of reasons for your cars behaviour, but it may well be too weak, and if it is, don't push it, because weak mixtures burn hot and can burn holes in pistons, as well as damage valves...
Roy
P.S. to answer Lennart, the lamps have to be down as the drag from them up, knocks about 20 kph off the top speed!