Update..... finally got time to look at this again and last test I did was swap carbs between #2 and #3 cyl .... not easy as it sounds...and the problem followed the carb.
You are right that just because a plug fires in atmosphere doesn't it will fire under compression.... plugs and coils have been swapped out.... have also ruled out valve adjustment now .... carb is coming off again to see what I missed .... thnks for reply
With air intake off ... it will pick that cylinder up if air is restricted... choked .... have had carb appart... cleaned , but see nothing wrong... am about to check valve adjustment.
Anyone had similar problem, with possible suggestions... thanks.
I am a honda guy ... Haven't had much to do...
I appreciate the reply and thoughts.... sometimes you need to set a job aside and spend some time thinking and hearing ideas.... I have been troubleshooting carbs a long time and these are some of the simplest which in itself can frustrate.
At times thinking out loud gets a person back on track
Well after cleaning last night and let set till today ... was able to properly set #4 this am... also may have been trying to set idle a little low .... may have been something lingering in one of the body passages..... but apparently cleared now.
Just went thru carbs all passages cleaned reinstalled and synched.
Here is confusing part .... engine runs perfect , but the idle mix screw on #4 carb has to be turned practically out to smooth the idle.... it has always been this way.... just removed and went over idle circuit again.... no...
On inspection there is lots of depth and thread for an extended length plug .... now just need to find one.
Edit... on closer inspection... only on one side... but I see there may be a 9mm plug available to go to larger thread
Update .... still have not found a drive that would for sure fit.
In the mean time I pulled the drive to do measurements... and the drive felt fine as far as not feeling rough or worn .... and started thinking that the grease may have started to dry out... over 25 years old... so put it in...
.ya it looks like aftermarket starters are readily available in all price ranges ..... all I really need is a drive or bending.... and it looks like drives are available.... the trouble is having confidence in fit