Timing Ignition for S92 engine 1600cc

Dear everyone,
I am a Daihatsu lover from Viet Nam. I have a Daihatsu Citivan (Hijet/ Zebra/ Espass… different name). It use 1600cc engine (S92). Because of Daihatsu withdraw since 2007, Daihatsu lover was on their own or mechanics experiences. My Citivan is hotter than normal after changing timing ignition by the mechanics (He adjusts with his feelings), so I buy a timing light gun to adjust and get some confuse. The picture show that Timing is 3 +- 2 ATDC / 850 +- 50 RPM. Most cars use BTDC but my car use ATDC?
I guess when adjust Timing, if I disconnect vaccum line and adjust in ATDC, when I put the vaccum line in, it becom BTDC? Is that right?

P/s: I don't have service manual for my car so …

Thanks & Best Regards

Hi and Welcome. Most of us on here are in the UK, where (AFAIK) we've never had this engine in a van. Whether our Netherlands friends on here have seen it I don't know.

PFM wrote:Hi and Welcome. Most of us on here are in the UK, where (AFAIK) we've never had this engine in a van. Whether our Netherlands friends on here have seen it I don't know.

Thanks PFM, I will take pictures. Because I don't have workshop manual, I am so confuse .