Changes in the weather affect the fuel/air ratio mix, will need I think a long 5mm Allen wrench to adjust - look it up. I keep one in my owner's manual so it's always in the car.
This might explain the cool weather to hot weather performance differences.
Also I think the pop-pop sounds are a too rich of a mixture. Be careful too lean and you will run hot and bad things could happen - look up lean engine damage. Better too rich than too lean in my opinion. If the exhaust burns your throat a bit, or smells like gas when you put your hand to the pipe then smell your hand it's running rich. The exhaust should smell close to any other car, best to use a meter not your nose but I have good, eyes ears and a good nose so I put them to work if nothing else is available.
I recall increasing the gap on my spark plugs, slightly larger than spec, this helped top to bottom rpm combustion but read it can stress the coil. The popping is un-burnt fuel being burnt somewhere in the exhaust system. If the popping comes out of the intake at the top of engine you could crack the airbox, and that can be a pain in the butt.
I also agree with "scary driving", you want to recheck your ignition timing, it's gotta be just right on these cars or they will do odd things, no six computers onboard to compensate (
like on a modern Porsche).
I had this problem before, will look up my old posts for you, could be of help.
EDIT-1:
Found an old thread about MSD and points:
http://forums.pelicanparts.com/porsche-911-technical-forum/163810-where-find-distributor-number.html
AndreasK, do you have the original "points" system on the car or an aftermarket kit like Pertronix Ignitor magnetic pick-up or Crane Optical Ignition?
All you have to do is pull off the distributor cap and take a picture, the guys here will know.
EDIT-2:
Quick fix for me was increasing the spark plug gap slightly, and leaning up the engine a tad.
I also redid the timing, but had to re-index my distributor to do so - a scary thing for me to do at the time, but Walter Mitty walked me though it with his excellent posts as I recall.
Are you running hot or any other symptoms?
What spark plugs are in your car?
EDIT-3:
The solutions I proposed might be better suited for popping/burbling/crackling when lifting off the gas quickly after hard acceleration. That was the problem I had years ago, not the original posters situation. Oh and I know nothing about re-gaping his style of spark plugs or even if that can be done. Old fashion NGK copper plugs are the only thing I've found my car likes.