Ok, I know exactly what I am telling you as I can picture it in my head, I don't know how well I can explain it though.......
You have put the arm on in the wrong position, really simple to sort out.
When you touch the pedal the cable pulls the arm, which in turn rotates the vertical spindle anti clockwise. Ok so far?
What you need to do is undo the nut holding the arm on, JUST ENOUGH so you can slide the arm up and off the splines on the spindle.
Start engine and be careful of moving parts.......
Leave the arm set against the throttle stop, you then want to rotate the spindle (might want to use pair of long nose pliers or molies)
You want to rotate it JUST to the point immediately before the revs pick up, hold it in this position , and using your hands/feet/mouth , manipulate the arm back onto the splines with the spindle in this new position. In effect you are moving the arm clockwise in relation to the spindle.
IfI you imagine 0 as being at idle and 100 being at full throttle, your spindle has rotated to far backwards so is working between -90 and +10, and anything less than the 0 just stays within idle range.
If you are anywhere near Exeter I can come over and do it in five mins, but easy enough to suss out yourself
