Aircooled VW South Africa

Hi all

just some advice wanted. When Im driving my 74' kombi it runs fine but if im coming to a stop or down a hill and i take my foot off the accelerator it backfires once or twice. Could it be running to lean or is there anything else I can check for

1. Timing

2. Leaking exhaust manifold

3. Leaking balance tube between carbs

Thanks Pine

Looks like there was a leak on the exhaust manifold. getting it sorted today.