Hi , have you checked the float for holes/leakage , not uncommon on the s12 carb. Failing this it’s either the needle or seat , very easy to fit on this carb.
“Undid the nut but after a turn or so it went tight.” ,
That’s perfectly normal , just keep undoing the nut , the idea being it acts as a self puller ,best to use a PRECISE fitting socket and bar, you may find that you will need a hammer to initially get it moving.
The most common carb is the one in picture 3 , the main adjuster is the one at the very bottom of the carb , undo locking backnut , wind in slightly for a weaker mixture.
Keith , I have a manual , somewhere , if I can find it , I’ll let you know , and you’d be more than welcome to borrow it.
I have a few spares for them , including Pistons and rings , and a complete carb , just let me know what you need.
One tip , make sure the crankshaft , and flywheel are THOROUGHLY de-greased beforehand , before de-greasing it does no harm to lightly rub the crankshaft with some fine abrasive paper.
Rather than confusing yourself further , try what I have said , and report back , as long as the points just start opening at 5/32 BTDC , it should be fine. You can set the correct point gap before doing the actual timing , it matters not whether anything is lined up or not , the gap will be the same any where on the stroke.
5/32″ is the correct timing for a 25c, as the 25c has an over centre spark plug hole it makes life far easier , just set it so the points just begin to open at 5/32 BTDC , tighten flywheel , RE-CHECK that it hasn’t moved during the tightening process……….job done.
