I've heard that the exhaust 'popping' on deceleration is a symptom of a lean condition. Also have heard that the GS500 from the factory runs lean. Is it normal for the exhaust to make the odd pop or will this cause a problem on the long run? It's not something I could even hear until I let my brother ride the bike up the street. The muffler does block it out when you are riding the bike, plus the extra noise block from wearing a helmet. Other threads on this yes, but I cannot find a clear answer. Something to be concerned about? Should I look into this before riding any more? Look forward to hearing from you guys.

Best wishes,
Andrew.

Nothing to worry about. That is if you're talking about a sort of random crackly popping in decel, that's normal and expected and doesn't indicate lean. It won't do it unless there is unburnt fuel in the exhaust, which is a sign of it running rich.

yes and no. If runnign quite lean you can miss a cycle (not enough gas to fire that cycle) and this unburned gas then does fire in the exhaust later.

But I agree, the statement that the GS is lean form the factory has caused many a wild goose chase. Look at any power graph/AF ratio and the most power is just on the lean side of stochiometric ratio.

FYI, try to put the choke on half way to make it really rich and see if it gets better or worse.

This could well be a leaky exhaust seal gasket at the header/cyl head.
Try fitting new seals, or at least nip up the nuts (but don't overtighten them!)