40hp 402 timing questions?

hi i posted in past about my 402 engine as it stalls when you punch it and i have dicked around 6+ hours adjusting the damn fuel mixture screw doing like 1mm turn and sitting for 10 seconds nothing frigin works.... the marine is 4 weeks behind so i figure i might as well tackle it.. i posted in past videos asking what this thing i tightened nut for no one replied i found what i guess is called a trigger so i dunno if the guy before me had it set right as he rebuilt motor but who knows if its done right.. how do you 1 know if that trigger is set right on the threading on the lever..

next i contacted mercury and asked about the timing they sent info but i confused as i been watching videos reading articles and everyone does it a bit different ..
it says Primary Throttle Pickup 2 to 5 BTDC
and says Maximum Timming advance 27 BTDC

then i have read you need to go 0.150 to .250" im guessing .25 is a 1/4" not sure what .15" be as i know 16ths be easier if it was like 1/8" from TDC you set it so i confused about that ..
as some say mark an inch back from TDC a white line... and some talk about counting teeth but i dunno how that help me..
as there is no markings on the fly wheel just what the guy marked on here and who knows if its right.. so i a bit confused... is there a timing for dummies and to know if that trigger nut i tightened if that trigger is in the right spot.. as i fed up with this engine i can not get it not to stall when you punch it..

if you punch it and pull back before it dies you can then punch it and it wont stall but only when it idles for a min say... and i have replaced the carb kit pump kit cleaned the screen and did this 1 1/2 turns till i blue in the damn face... and nothing is working right...

i still gotta get a timing gun as they are 250 bucks so i gotta invest in that as no one has one i know of ..

so any artickles for dummies be great and a flywheel where you have no idea where the marks be except when person used 2 white lines one says TDC but thats it

here is a video i took yesterday 12 min but i show what steps i have done shows the idling issue i show i set the carb but not the 1mm every 10 seconds... and shows how when you punch it stalls first time.. but punch it a second time she accelerates so thats why i thinking timing only thing i havent done... and my compression is 150psi per cylinder ...
and that trigger thing i not sure if guy had it in right place??


i emailed my marina for a manual as they get the selco manuals so hopefully they can find if they can get me one

but here is that video
https://youtu.be/WqNwbUh9tic
as i frustrated and it cant be this hard to do

i was talking to another mechanic showed him video where i should you guys how the trigger arm nut was loose thats goes to under the flywheel and says probably my engine is outta time...

but he wouldnt help after that said 100 bucks an hour

so as you saw in my orginal videos a month or so ago that Trigger arm that nut was loose and that rod was sloppy moving so i tightened it up..
but how do i set that since i bought engine off a guy supposedly running but when i got it ran like crap... so how do i make sure that trigger arm is set at the proper spot.. i have only seen about timing but never about the trigger..

whats the procedure on a merc to set the trigger lever arm so its in the right spot so then i can get a chance to fix the timing

i still waiting back from marina to get a service manual

but i googling and no one has anything on setting the trigger plate linkage
im guessing i need to pull fly wheel off

and then should the trigger thing move fully forward to the throttle when it is full wide open... at WOT... as i cant find what is the proper setting for this