Before I tuned some of it out mine went off like a gun,,
I pushed down on the sidestand just enough to cut power to the spark plug & let off when I saw 2 cops in a yard.. They both looked like theyd been shot at..& OHH yea they looked at me,, but they count know I did it.. or that it was on purpose,,

Yep I had the, "Ka-Pow" boom on shutdown.
Now it's gone ! (6 times replicated the situations it had happened)

Read all the artitcals about it.

The "brass plug",  was gone.
So on idling, 1050 RPM, I played with it, going in and out,
Could hear no difference.
Then reading more, found someone said, if the idle is to high
turning that screw doesn't make a difference, because the idle is to high.

So later, I adjusted the idle down to (Just know it was 8-9 hundred)
Now, I could hear the, gas mixture screw make a difference, in in and out.  kept turning out,  the RPM's increasing, tell they started to decrease, then went back to the highest RPM.  (By Ear)

Rode it.   "Ka-BOOM" on shut down.   Hmmm,
Next I am thinking to tackle the TEV on the Carb.
(The two PO's ran crap gas, so thinking that at least needed a good cleaning.)

Then, let's double check. Put just a wrap around the spark plug tack on, and lowered the RPM by the 'throttle screw', to 800.
And played with the 'idle gas/air' screw, (under what used to be the brass plug), and I adjusted it to 1/16 of what I did by ear.

Didn't really want to tackle the TEV, but didn't want the big 'Ka-Boom",
Cops in this county will pull you over if you smell, scotch tape.

Then one night, 'amber fluid in hand of course'.
Went out to the shed, and decided to take out the muffler bolts that go into the head, and give them a shot of 'anti size'.
Just so they are ready when I decided to check the cam chain tensioner.

Found my stool, got the right socket, just double checked, that it fit the top bolt. Yep, it fits, then put it on the bottom bolt, and it turned !!!!

WHAT !   No way did they put two different size bolts in their.
Well they didn't, I turned the bottom out by hand, then lubed it, put it in finger tight. Took the top one out, it needed the ratchet for about 1/32 of a turn, lubed that put in finger tight.  Then put the ratchet on, and, 'firmed them up', to a point, just from experience in running a steel bolt in a piece of threaded Alum. (About 1/4 turn)
Both bolts were Shiny New, they looked Like they were just picked out of the bin.

Now, YES MOM, I know, (KaBoom = Check Muffler tightness first)
I did, but by only grabbing every part I could and trying to wiggle.
No Wiggles, so no looseness, air leak. (I Thought)

Then I put a wrench to the clamp, where the muffler goes on the pipe.
Yep, several turns to make it tight!

Now, 6 times, consecutive, no "Ka-Pow" on shutdown.

So, my suggestion, for Kapow,  Check Muffler, for air leaks,
by Wrench, Not hand !  Then adjust screw, (under the brass plug),
with, Low idle. Then if that does not do it.
Keep chasing.