high idle/popping on over-run

[Mk2Tony]

Ok so I had a plug/lead break down last week which was causing a misfire/backfire whilst driving. I changed the spark plugs, leads dizzy cap and rotor which solved the issue.
Great! went for a run from Cardiff to llandysul for the weekend, went up there and back lovely cruising at 50-60 all the way was running lovely all weekend, now when I went for a quick run locally last night it seems to be idling fast and I'm getting a popping from the exhaust on over-run.
I didn't get chance to check it over last night but I'm hoping its maybe a loose vacuum hose or something like that? Does anyone have any ideas as to what it could be or have come across the same sort of symptoms before?
It's a 2ltr CU Aircooled engine

Cheers in advance for any help

Tony

[Mk2Tony]

found a big split in the balancing vacuum hose linking the two carbs, cut out the split and re-attached running sweet as a nut again now, will pick up a nice new piece o pipe today. Also replaced all of the small vacuum hose bits whilst I was in there