I just wanted to share with you all my recent experience in modding my daughters Shinima 150. Maybe some of the difficulties and solutions I experienced will help anybody who attempts these mods.
The Shinima 150 is a GY6 clone engine, auto trans with reverse. There are a couple of different Chinese GY6 clone 150 engines. From what I could find out one engine is a 157QMJ and one is a 1P57QMJ. Mine is the "P" model. It makes a difference on some parts, particularly the head and cylinder and cam. Your engine model number can usually be located on the left bottom side of the CVT cover. It will be stamped in the metal.
The stock version of the Shinima 150 was a very dependable, though under performing machine. It had emission control parts and a catalytic convertor in the exhaust pipe which had to rob some of the power.
The first mod was a Prodigy teflon variator with Dr. Pulley sliders, MRP main clutch spring(yellow), and MRP clutch shoe springs(red). The variator was overall too big around and would rub the side of the engine case so I had to take it to a machine shop and have the circumference of the variator decreased by approx 3/16" and then it fit fine. I'm not sure if this was because my engine was the "P" model. but if yours is the "P" model you might want to watch for this. This mod allowed the engine to rev higher before the cluth engaged and it came out of the hole quicker and it picked up a little on the top end.
The next mod was to do away with the stock airbox and install a Uni filter directly on the carb air intake with about a 5 inch air tube, which I cut off the stock airbox. I also did away with the stock exhaust pipe and muffler and added a bigger pipe with a bolt on FMF muffler. The stock pipe was 7/8" OD and I ordered a new piece of pipe that was 1-1/8" OD. I also eliminated the emission devices and the catalytic convertor. I took the new pipe along with the old to a metal fabrication shop and had them bend the new pipe to match the old one. They left it a little long on each end to allow me some room to properly fit it on the machine. On the engine end, I had to remove the first 4" of the old pipe and reuse it because of the way it fit into the cylinder head exhaust port. The new pipe was too big to fit in the head without removing it and having it machined. I re-attached the piece of the old pipe to the head(be careful not to lose the sealing washer that fits up in the head)and then fit the new pipe on the ATV with the new muffler. I adjusted the new pipe to where it was not touching the frame anywhere and then marked where to cut each end of it for the best fit. I cut the new pipe and again fit it on the ATV with the muffler attached to its frame mount. Once I was satisfied with the fit, I tack welded the new pipe to the old piece that was bolted to the exhaust port on the head. I then removed the entire pipe and completed welding it to the old head piece. The engine would now be breathing alot better than stock. Since it was getting more air, it also had to get more fuel so I added a bigger main jet to the stock carb. The stock jet was a 112 jet and after consulting my parts dealer. we decided to go with a 128 jet. The 128 made the ATV run good until 3/4 throttle and then it would start sputtering. I wrongly assumed that the engine still was not getting sufficient fuel so I installed a bigger 132 jet. It was immediately obvious that this jet was wrong because the ATV now began sputtering at about 1/2 throttle. Another consult with my dealer and we decided to go smaller on the main jet so i installed a 125 jet. There was much improvement, but still the engine sputtered at about 7/8 throttle. Another jet change to a 122-1/2 jet fixed the problem and the ATV ran like scalded dog!
I confirmed the lean/rich mixture of the carb by following the throttle chop instructions posted by 2manytoys on this forum. These mods made a huge difference in the performance of this ATV. It was paced by my friends car at about 36mph. which was a huge improvement over stock. The low end power is phenominal and the top end is great. My daughter took it for a test run and couldn't believe it was the same ATV!
I hope this may help anyone looking to mod your Chinese ATV. If you would like to know any info as far as parts suppliers or any other questions, feel free to email me at BSpray29@yahoo.com

 

Nice post BSpray29. I printed it out and have stored it in my 150cc binder for future reference. Thanks for taking the time.

 

will print and read lata

 

ok i bought a 90cc atv (xtreme w/gy6) with a blown motor for my son. i purchased a brand new 150 gy6 from ebay and installed it. it runs good but i was told i should upgrade the exhaust. does anyone know of an exhaust system that would fit right up to the 90cc frame without being modified? or does anyone have a suggestion of an easy solution to this. Also i left the original cdi box hooked up because the new box seemed to have a little bit of difference in the clips,will this make a difference in the motors performance? If anyone had some advice to get the most out of this little atv (with in reason) I would like to hear it!!!