How is the spring tension tested? Will they measure out to be a tiny bit shorter, or can they still be the proper length but too weak?
This is the procedure:
With the normal springs removed and a set of very soft test springs installed measure the length of the spring when the valve is closed. This measurement is called the 'installed height' Then you get yourself (borrow) a valve spring tester. Basically, it's a small set of scales that measures up to a few hundred pounds. Place the valve spring tester on the table of a drill press, and place the valve spring on top of it. Get on old valve and place it in the chuck of the drill press. Now turn the handle on the drill press and squash the valve spring. Using a vernier to measure the spring length, gently squash the spring until the height of the spring is the same as the installed height of the spring, then read the pressure on the gueage. This is your 'seat pressure'
To work out the length of the valve spring when the valve is open subtract the valve lift (less the valve clearance) from the installed height. Now continue to compress the spring until the spring is this length. Read the guage, this reading is the 'over the nose pressure'
I can say that Kibblewhite valve springs are good. Had a set in a modified ZX7 ninja for years, they replaced the APE items which didnt even last a year.
Believe it or not, but if you run a 2 valve Kawasaki
Pro Stock Bike, valve spring need replaceing every meeting !!! (thats less than 3 miles riding)