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Thanks Ben... Can you help me understand the decompression function a little better...  what I am struggling to understand is, if the decompression function is causing the exhaust valve to remain open slightly, ( during the "cranking" phase), then why is it I can have 145psi of compression when testing such.  Seems to me that I should have far less compression if the decompression function was malfunctioning.   I will pull the old weights to check for wear patterns, and attempt to make the same patterns (if any) in the new weights.  Hopefully I can get to that tomorrow.  I'll keep you informed as to my progress. 

We eliminated the thermostat and according to Hisun back when we were pulling our hair out with overheating, their rep told us they stopped using thermostats and relied on electric fan to control warm up. 5 years now mine has none. At all.....it works here..but we don't have snow and below zero temps to deal with. Takes a little longer to warm up but has never overheated again.

I sure wish you had been around back when I was fighting with mine .I was at the mercy of the only mechanic in my state that would work on these..He was good but slow as paint drying. I learned a lot from him and have managed to keep mine going since. Glad to see you taking the time to help this guy.. We need more members like you.. Thanks from all of us dumbazzes that bought Massimo/ Hisun

I assume the new latest pics are the new cam and head assy?????  It has a problem!!!!!!!!!!. Poor mfg process information (instructions and drawings) never really go away.  They always pop back up like the turd they are.  I was flown to Mexico for multiple "mistakes" and to T/S with a "fix and rework"---clean up the build information----and only to find the same problem pop up again 6 months later from the sister supplier,  This problem was on both Yamaha Rhino and Hisun cam assys a good 5 years ago.  We had Massimo.  Another shop had Yamaha.  They chased a mystery problem to the cam assy.   My new cam assy arrived (with the same runability problem) in the newly uncrated unit..  I did the carbide burr air tool hand mill job on both sets.  EXCESS WELDED WEIGHT GONE.  Other shop has same problem.  His flyweights had all the same machining, stamping marks...with welds identical.....the same sub supplier.  My reworked flyweights were given away to fix the Rhino. Since you have the old cam, mark the flyweights to MATCH their wear "home" location.  Remove and you should see the rub marks where the little disc hits the rear welded/attached weights. For the fun part:  you can do it. 1.  Hold the whole cam assy and put the button head pin that sticks thru further to the inside by the exhaust cam lobe DOWN.  Gravity is your friend. 2.  Put your thumb on the button-----should push in below the cam "shaft" profile----as in not the lobes profile----Rotate the disk and the mini cam will push up the button. 3.  Reverse and the button will retract again into the cam shaft area. See how the system works.  Flyweights pulled in by springs...sling out with rotation speed.....disengage the decompression pin.....at engine stop, the springs retract the weights but cannot due to the excess welded weight material profile rub with the small disk. 4.  Pull out the small disk with the 2 flyweight engagement pins. 5.  The "rod" attached (with the dogleg bend) is the minicam within the cam----used to push up the button pin that hits the extra tab on the exhaust side of the big valve cam. 6.  With this pin out, the button can now fall into the hollow main cam center.   Gravity----set down cam button down.  If it falls to the center, no big loss.  Just a pain to reinsert it into hits hole....ship in a bottle syndrome. 7.  You should now see why the your adjustment is wrong.  Rotation of the of the flyweights, rotates the small dime sized disk, which rotates the dogleg rod inside the hollow cam. 8.  YUP, the end of the dog leg is what pushed the pin out further to engage the cam.  BUT. if the small disk cannot fully rotate backwards, the button protrudes out too much and now does a compression release. 9.  Your thinking now, why not just make the disc smaller in diameter........NOPE, not enough meat left for the pin hole wall thickness. 10.  Reassy is just pushing back in the dogleg rod (with the decompression button facing down) and the punch mark up as used in the timing mark. BTW, use a small 6 inch scale to use as a straight edge to line up the cam bolts, alignment dimple and the cast timing mark in the head. BEN

Dennis See post 10 and 11 for shifting and 15 to adjust belt