the timing inspection cap is located on the top of the engine on the left side ,between the carbs and where the swingarm hinge is located . Its about an inch around and has a large slot for a flat screwdriver .
Forgive me, but I don't see the connection between your engine's timing and the timing belt tension....
On my '85 the engine timing is not adjustable. The timing belt tensioners ARE and when set right there should be 1/8-3/16" of movement in the center of the long run of each belt with 4-5 lbs. of thumb pressure.
I recommend you post your question over in the technical section. Most of the gurus won't see it over here, and a lot more people frequent over there. Just a few of us greeters hang out over here on a regular basis.