Trapped compression is the amount of compression that your engine makes once the piston covers the exhaust and kips ports.
So, once your piston is on it's way up and closes off those kips ports they no longer play a roll in compression.
Ok, what makes the compression after those ports are closed?
Piston, ring, cylinder wall, gasket, head to cylinder mating surface, spark plug threads, spark plug, and the cylinder to head alignment pins.
It's gotta be there somewhere.
Remember, you can remove your kips valves completely and all you will loose is your bottom end to mid range power.
The top end power will come on like a scalded monkey butt.
Start with the cheapest and easiest thing first.
Replace the plug and make sure it torques to specs.
Then I would pull the head and make sure that the alignment pins are not too long and the mating pin holes are clean and free of debris.
I would mic the cylinder wall and have someone who knows what to look for inspect your cylinder.
If the cylinder mics correctly and there are no flaws in the plating, and if the piston walls are cherry, I would as a minimum replace the ring, lap all the mating surfaces, inspect and replace any kips parts not in spec, and clean it all up to look better then new.
Then use new gaskets to assemble.
Of course with the cylinder off I would check the crank to connecting rod clearance with a feeler gauge and compare to the factory specs.
If it is out of new spec, I would plan on a complete rebuild.
Upon finding anything not in spec with the cylinder or piston I would pull the cylinder and clean up the transfers, bridges, ports and boost ports, studs would be removed, the cylinder would go to the plater, head would be re-chambered and compression release installed, lapping of mating surfaces would be done, new Wossner piston kit installed with oiling holes, new cylinder studs installed being careful to chamfer the stud holes, using only Cometic gaskets, everything cleaned to look better then new, and everything torqued to spec.
Probably missing a step or two in there but you get the idea.
Then again if it was my bike and it was a 86, I'd clean the air filter filter and just rebuild the whole motor