how do I defeat the auto decompression

I am in the process of "uncorking" my newly acquired 2001 XR650R and doing a complete service at the same time. I stumped myself yesterday while attempting to do a compression test. Service manual says about 87 psi normal after 5-6 kicks with the kick-starter which is exactly what I saw. Then says 160 psi with the decompression disabled or so I thought, but how do you do that since that function I think is automatic and is performed at the camshaft during a kickstart? Do you have to hook up a compression gauge and push the MC down a hill or what? How can you check the regular compression? At first I paniced and thought I had a problem with very low compression (87 psi) then I remembered the decompression during that kickstarter ops so please help this old 68 yr old man out. I'm stumped.
Thx
Mike

I'd say you dont need to disable it if you have it installed. The limit with it disengaged would be for a bike that has had a 'hot cam' fitted which no longer has the auto decomp built in.

I might have asked the question wrong. I don't want to defeat the auto decompression permanently, only want to check my compression and I don't see how to check it without the auto decop interferring. I'm not sure how because the shop manual doesn't tell how.
I thought about pushing the whole bike down a hill with the compression gauge hooked up, but not looking forward to pushing back uphill to shop where the whole thing started. Kindly remember my age. Just shy of 70.
How do ya'll check yours?
Thx in advance
Mike

Take spark plug out...attach compression gauge...hold throttle fully open...start kicking.


If solo, set up camera or smart phone to record compression readings.

to get a max available comp test, you need to set the exhaust tappets with 1-2mm clearence, this stops the auto decomp from affecting it, remember to reset them at correct clearence afterward

That should have been......."Thank You, that makes sense". And it does.
Mike

I have learned something new today , thanx to T kiwi this time