I'm just one of the regular members here, having owned 4 Chinese tractors over the last 10 years or so. I'll admit up front that none of them was a Foton. But some problems are fairly universal.
The description of what you did to the clutch is unclear, but I'll have to assume that you did so without really understanding what those adjustments did (or didn't). The two most common problems that inhibit smooth PTO engagement are (1) incorrect gap between clutch release fingers, and (2) not enough pedal travel. There are more complicated reasons, but these two have to be checked first.
With the tractor parked and the engine off, open the clutch inspection window. Tell me if you have a six fingered clutch or a three fingered clutch. If it's a six finger, the closest three fingers are for the main drive and the other three are for the PTO. Then measure the gaps between all three (or six) fingers and the vertical face of the throwout bearing - and post the numbers here.
Also. How many manuals came with this tractor, and what is each for?
//greg//