Hello I have a few questions about trying to tune my twin 45 side draught webers.

When I use a lenght of hose in the front carby both barels sound like they are sucking nice and clearly but on the back carby they is a fair bit of popping going on and the engines ideling really rough? any hints to help me out?

thank you, Paul

Assuming float levels are correct (8-16mm) and same correct componets in both carbs.......

Check gaskets for air leaks on rear carb by spraying carb cleaner around gaskets and listen for engine speed increase.
Check balance using hose to listen for pitch of air flow. All throats should sound same pitch.

Next would be to check idle jets are correct size for engine spec.

A pop or slurp instead of a hiss usually means that the fuel isn't as fine (not atomised).

Make sure everything is clean and there are no leaks.