My head gasket appears to be leaking oil. Will this cause the engine /exhaust to pop when shutting off when running at low or high speed ?
Sorry to hear that my friend.
Are you sure the oil leak is from the head gasket and not the rocker cover? If it is the head gasket there is only one cure and that is a new gasket and possibly a surface grind on the head to make sure you have two flat mating surfaces. If the popping and backfiring started at the same time as the oil leak then it could be the head gasket if so it will also be constantly weakening the fuel mixture and eating away the remaining gasket seal at each firing stroke. The repair is to strip the top end down and use the top end gasket service kit to replace/renew all seals etc. Be careful to undo and torque the head bolts in the correct sequence when rebuilding to avoid warping the alloy head (also clean the threads with wire brush and run them down by finger to make sure there is no thread friction).
Hopefully it is the rocker gasket which is a much easier job.
Good luck with it and hope it manages to make Alexisbad next week.
See you there.
PS If the head is warped a little you can carefully 'grind' it back yourself using 400 then 600 wet and dry on a sheet of glass, look for a nice even grey finish.
I really doubt that the cause for the oil-leak is the head-gasket. In my 12years of Bulldog-experience I never heard of a leaking head gasket! Much more common is a leaky rocker cover on the second cylinder (faulty o-ring inside the cover or one of the two screws is not tightened correctly)
The popping exhaust has absolutely nothing to do with the oil-leak! This popping usually comes from a lean ( too much air, not enough gas ) mixture. To remedy this you have to look at the intake side of the engine (when the engine is idling spray brake-cleaner onto the hoses to and from the carburators. If the revs change, you have found a leak and can go on from there. If the revs stay as before it gets complicated)
Why exactly does this popping bother you?
Cheers from Germany