Hi, You seem to have followed the instructions in the book, or it wouldn't run at all.

I use an eyepiece, similar to what a watchmaker would use, and even then it takes time and patience.

Go for the "best fit" possible. Even the book admits that some engines will run on the first notch, and some wont.
I think that a big magnifying glass would be just as good, maybe a bit clumsy to handel.(one hand for the glass, one to hold the motor, one to hold the lock nut, one to adjust the valve, one stop you falling over with frustration)

Mick