slight misfire

[Mk2Tony]

Hey guys, took my van out for a run to pick the wife up yesterday and noticed a slight misfire, only seems to be at low revs, also get popping on overrun. I have had a quick look, checked the vacuum hoses etc but couldn't see any obvious splits or leaks in the pipes. Its a 2.0l CU, just hoping someone can give me some pointers on things to check for or may have come across the same problem before?

Any help greatly appreciated

Cheers

Tony

[Mk2Tony]

Ok so I have changed plugs, fuel filter, checked all vacuum hoses for leaks and done a compression test which seems within parameters, cylinder 4 is slightly down but not enough to cause an issue, seem like a worn ring after doing the wet and dry tests.
Have found a couple of blows in the exhaust, one from each flange where the silencer bolts to the heat exchangers so this is possibly causing the issue? next port of call tonight is to check the vac advance on the distributer, can anyone advise me the best way to do this as I'm not too confident in taking the dizzy apart, or do I just need to take the dizzy cap off and suck on the hose to check if the vac advance is working?
Another thing is I have twin webber carbs, so the vacuum only goes to one side of the advance unit, and the other is blanked, is this correct, although it has been like this since I purchased the van and the problem only arose last weekend, seemingly over the space of a few hours whilst being parked up!

Any help or info greatly appreciated

Tony

[CovKid]

They don't like leaks in the exhaust system. Work on solving that first.

[Mk2Tony]

Cheers Covkid, I've ordered a new exhaust today, just waiting for it to arrive so working on checking over any other bits and pieces that might pose a problem just to eliminate as much as I can

Tony