Unfortunately it is a design problem in these Chinese bicycle engines. The clutch handle radius should be a little longer than it is. So, if you adjust the cable so that the clutch doesn't rub (create resistance) when you have the clutch handle being held by the pin (not pulled all the way in), then this will cause the clutch to actually slip alot if you have a powerfully modded engine (7 + HP), during extreme acceleration. There is a spring pressure adjustment under the clutch cable post (it is removeable) and it is possible to deal with this problem to some degree by tightening it. Unfortunately it is easy to overtighten it and if you tighten it enough so that the clutch never slips even at optimal cable and daisy nut adjustment (during extreme acceleration), then it means that your spring pressure is so high that your clutch pin will become 4 mm shorter and stop working(even after multiple tightenings) and will have to be replaced every 5 - 6 days with moderate riding. I used special conrod stud bolts for good steel and made several of these stronger clutch pins and tempered them with a blow torch and oil repeatedly. Still yet, with the spring pressure high enough so that the clutch never slips when the clutch handle pin can hold the handle so the clutch doesn't rub and the clutch doesn't slip during high tourque racing like loads, these little special made super tough clutch pins also wear out in no time. So I had to release some of the pressure off of the spring in the clutch mechanism. What I did start doing was to continue using the super tough clutch pins (tempered high strength steel, speed steel), and at the same time I always hold the clutch in manually(when pedaling/coasting). With the cable adjusted so that I have to hold the clutch all the way in to prevent rubbing(resistance), I was able to acheive proper functioning of the clutch so that it doesn't slip when under high torque load/gnarly acceleration -with occaisional wheelies n stuff. Now after I got all of that sorted out, I discovered that with my new big 22mm carb, I could actually pull the clutch in just a little/enough and let it slip on purpose while revving the engine way up there and it will actually begin to accelerate really fast. Incredibly and frighteningly fast! I purposefully started letting the clutch slip a bit to acheive this, but it is all controllable by squeezing the handle how much I feel I need at each mili-second. It does not slip at all if I don't want it to.
If you have not built your engine for maximum power with a specially tuned pipe, then you can just adjust the cable and daisy nut on the clutch and you will be fine. If the factory personel accidentally forgot to adjust the pressure spring to "within ballpark" adjustment, then you may have to access that hole under the clutch cable post, insert small screwdriver at angle-out(snag the slot) and push the bike back wards 1/2 a wheel turn while the clutch is engaged. You will feel the spring tightening through the whole bike/your hand on the seat i.e.) If you overtighten it, you will regret it. It is very difficult to get that cable threaded back through the cable holder post becasue it is all crimped up from use on the end. So accessing the clutch spring pressure adjustment is not convenient.