Originally Posted by Beemerboff
When Rob Farmer was chasing a mixture problem he fitted a "O2" meter to his RS? which he could read out on the road, and found that the flat filter didnt flow enough at high revs , and stuffed up the mixture.
He fitted a old style round filter which flowed better, and didn't affect the mixture as much at high revs, but it still wasnt perfect.
I spent some time on the Dyno with my PD seeing what worked and didn't work
The flat airbox was spot on for bikes fitted with 32mm carbs but just didn't flow enough air for my 40mm carbed bike.
The problem I had was the lack of main jet sizes for the bings. The early airbox made the mixture too weak at the top end and I couldn't buy main jets in the right size to get it right.I really want to fit a set of Amal mark II carbs before I start messing around again.
What you do appear to get with the early airbox, as long as you have the higher comp pistons, is a much more linear power delivery.
My PD going though it's paces. You can see the early airbox.
I also had it rigged with a air/fuel ratio meter for road testing
This is an interesting read