As part of my top end rebuild, I replaced the cooling fan on my type 4 engine as my old one had missing blades. Bought one from @Zed to fit. Before fitting, used the Ratwell article (https://ratwell.com/technical/FindTimingMark.html) to check that the timing mark was in the correct place (it was). Fast forward to last night and I was having a tidy up and found the old fan. Decided to check the timing mark on that to find it was off by around 1mm (this would have resulted in a difference of around 2 degrees when setting the timing). So when I was setting timing to 7.5degres with a light, because the mark was in the wong place, it would mean the timing was actually set at around 5.5degrees. The engine still runs at this point, but the spark is happening a bit too late. In hindsight, this would explain why the van never felt like it was running 100% (1st air cooled vehicle so had nothing to compare it to). So, when setting your timing, make sure you check that your timing mark is in the correct place.
