Restriction

[Steviemeaks]

What items restrict post august 77 bikes

[fizzydoctor]

It is mainly the exhaust, which is reduced to 28mm from 32mm, if you fit the earlier one piece exhaust you should see some improvement

[pertheswede]

There was also some restriction in the cylinder on the early UK FS1-E's (73-77). They went from having a 6hp "FS1" cylinder to a 4hp "F5B" one, which had worse porting etc

[Steviemeaks]

Cheers for this lads helps a lot