loss of power?

I have just had my 4 blowing injectors refitted with new seals and washers. they now are not blowing. But the power when i need it isnt there, i have have had it checked by a local garage on a small engine fault finder and everything checks ok.On a run it does 65mpg with 4 up but put your foot down and nothing just a slow build up of speed the urge it had before isnt there. Can any one help please