Ok , i have just installed a nosram rs .18 evo in to my hpi mt2 everything is installed correctly. and i am using the stock mt2 servo and linkage

the carb is constantly just over halfway open and when started revs constantly none of the screws make much of a differnce, when the accelerator is pulled it opens fully and then goes back to halfway, but when the brake is pulled it closes a slight bit then rests on fully opened

I am completly puzzled any help would be graet.

You should post a few pics. It could be a radio problam ( were is trim set?, or end point) Is there a spring set up on the linkage?  Can you manually close the carb? Should the carb have an outside spring? Are you in the wrong servo hole? ( servo to horn?)

pics here, i can manualy close the carb but not all fullty by about 3mm, no spring on linkageand there is only one servo hole

Seems to me that you just need to adjust the trim or the linkage lengths. Just turn the power on and adjust the linkage until it closes to where it will idle

Ok, here is the issue. The throttle arm on the carburetor is adjusted differently than the one on your stock motor.

Remove the carburetor. See the arrow in the picture I posted? Its pointing at a nut. Loosening that nut will allow you to adjust the arm. If you still have the stock carburetor, adjust its idle screw so there is a 1mm gap. Adjust your new carburetor so it also has a 1mm gap. Move both carburetors to their idle position. Now adjust the arm on your new carburetor so it matches the old one. Install it back into the car. Now remove the servo horn from the servo, power on your radio and receiver, move the idle trim to neutral. Put the servo horn back on the servo making sure the carburetor is as close to its idle position as possible. Adjust the throttle trim on your transmitter to take care of any small adjustments that may be required.

If you dont have the stock carburetor, then it will just take a bit more trial and error adjusting that arm to the proper position.