Loss of power and mis-fire

check the delivery of fuel first but you havnt said whether it is mechanical or fuel injection but if delivery of fuel is low then you need to replace the fuel pump and filter but if its mechanical fuel pump then get a empty pint bottle and turn pull off the fuel pipe feed going to the carb and put this in to the bottle and then turn the engine over for about 10 seconds and you should have a half/three quarters full bottle of fuel if not you have a poor pump to replace it will cost about 15 to 20 pounds but remember to get a filter aswell if it is mechanical and it the same principle with the fuel injection set up