If your Kombi is running a 009 centrifugal advance distributor or even the original SVDA and you are suffering from the common flat spot, you really need one of these new SVDA distributors.
Replacement SVDA distributors were typically very expensive and hard to come by which is why they were often replaced with the 009 distributor. Now they are easy to get and in-expensive you should think about replacing yours now.
Running a 009 can cause flat spots and lean running which can lead to overheating.
This single vacuum dual advance (SVDA) should solve your problems. You may need to have your mechanic tune your carburettors, but once you've done it you will be amazed at the improvement.
We have used these in our own Kombis so we can testify to their quality.
This should work with all Kombis 1968-1979 1600 - 2L.
Part number: 043905205R