I use one of these .... https://www.ebay.co.uk/itm/Top-Dead-Center-TDC-tool-Timing-Gauge-14-mm-thread-high-quality-in-best-price-/201984173362?_trksid=p2349624.m46890.l49286 For a stock engine with dished pistons and no head shave you may have to make a new longer rod for the end of it - I can’t be sure but good to be aware of it. Not sure about your carbs but my choke cables not only move the jets down but they have a slight effect on the butterflies. You seem to be experiencing a lot of strange issues, so the idea is to remove anything that is potentially contributing, until you get to normal idle! Then connecting things back to how they should be “one at a time” and testing at each stage. That way if the revs rise when you put back, say the choke cables, you know it’s them to blame / sort out. With these things it’s often just the simplest thing that you eventually discover, keep at it, you will find the culprit!