by Adam_Winstone » Tue Sep 27, 2016 9:44 pm
Pal of mine fitted a slope back seat to a GP that he restored and it seriously limited the airflow under to the original airbox, so much so that when he took it to have it dynoed they couldn't get the motor to breathe cleanly as regardless of whether the air/fuel ratio was correct. The motor simply couldn't breathe enough volume of intake and he was given the option of changing the seat or the intake system. He swapped to a remote filter and the running and jetting requirement instantly changed.
I'd suggest that you have the same decision to make, change the seat or change the intake.
Adam
PS - You're not the first to make this mistake, nor will you be the last.