164 carb ignition timing

[TonyCy]

A strange one - or is to me. Perhaps someone has experienced similar and hence has ideas. I’ve rebuilt the 164 engine, refitted, statically timed at 10d btdc. So far, so good. Distributor was put in with drive aligned as per book, at cyl1 TDC rotor pointed to 1 plug on distributor cap. Engine starts and runs well, so this morning set up to check dynamic timing on cyl 1 by strobe and 10d btdc mark on crank pulley. What did I find? Way, way out according to this? And ok way to bring in line without engine running rough. In fact, runs smoothly exactly where it was statically timed and falls off either side when I move distributor. Vacuum advances both off. Idling at 800. Dwell low and I need to correct but I don’t think that’s likely to cause perhaps a 10-20 deg deviation I’m seeing. Puzzled.....

One thing to add. When I opened engine initially I found that the timing gear was one tooth out which I corrected. I’m starting to wonder if there was a reason for that! But that would also mess up valve timing if out by one.

Anyone any thoughts?

Cheers!