Disco v8 exhaust popping

Popping from the exhaust when warm its a 3.9 v8. does it on tick over and then really bad on overrun.

changed
coil
leads
plugs
head gaskets
checked valves (all seal)
rotated dizzy and it gets alittle better anticlock wise but comes back.

Any ideas guys

Manifold air leak can cause popping so can a lean mixture.

I used to get an irregular pop pop pop pop pop on tickover when cold.

I think the igntion timing was out slightly, was a while back but I had igntion problems soon after I think.

Also, mine does it quite a lot when it's warm on overrun, kinda normal though for a fuel system which doesn't have a fuel cut overrun (although the throttle is closed, the ECU still squirts a bit of juice in according to engine speed. Modern cars shut off the injectors when the ECU detects overrun)

Get the igntion set to somewhere between 0 and 6 degrees BTDC (depending on what runs best) and then the rest is probably normal