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Trinity's 90cc Motor Build Up

Alpha Sport ATVDoes your kid ride a Kasea, Predator, or an Alpha Sport? How many times have you heard this before, "Dad, I want to go faster?" I know I have gotten sick of hearing that from my daughter, so I decided to do something about it.

There are a handful of companies out there that specialize in the world of kids ATVs. After numerous hours of talking with various companies we decided to send our motor out to Trinity Racing to have them do their magic. The Tech Person at Trinity was very helpful in pointing us in the correct direction for our motor project. The motor package that they recommended, consisted of a Trinity Stage IV Aluminum Head, mild cylinder porting, Trinity Stage IV pipe, 20mm Keihin Carb kit, K&N Air Filter, and new clutches. All these components are complete bolt-ons without having to split the cases.

The stock head on our Alpha Sport is of a very poor design, to which we are trying to get maximum performance out of. Although the head can be improved by having it cut, it still is not as good as a Trinity’s Stage IV Aluminum Head. The aluminum head cools better and is lighter, given the ATV reduced heat buildup which helps keep power at a constant.

Trinity also does a wide range of porting on these cylinders. For this project, we wanted to keep the machine ride able so we chose a mild port work. By doing this, we left our options open for more power as our rider gets bigger and more experienced.

Next on the list of installations was the pipe. For those of you that have never seen the stock pipe on this ATV, it is basically a straight pipe with a muffler clipped on. This setup hinders performance and is also very heavy. The Trinity Stage IV pipe is a 3 pipe design in which the stock oil tank and battery box have to be removed. With the tight confines of these quads there is just no other way to route it to achieve maximum performance and to keep the rider protected from getting burnt or getting the pipe damaged during normal riding conditions.

Now that we have the cylinder and head setup for more performance and a quality exhaust to remove the spent charge, we need to feed this thing. For this, Trinity opted for a carbon fiber reed cage setup and a 20mm Keihin carb with a clamp on K&N filter. The K&N filter is a nice replacement over the restricted stock airbox setup. For a motor with this potential, replacing the stock carb and reeds with this setup will not only improve performance, but will also make it easier for fine tuning adjustments. All jets are readily available for this carb at any aftermarket distributor.

Alpha Sport ATVWe now have a motor combination that puts out considerably more power. Therefore, we need to address getting this increased power from the crank to the ground. Unlike most Sport Quads in which it would just be a matter of changing the gearing, these ATVs use a CVT setup. It doesn't matter how much power the motor makes, if these ATVs are not clutched properly you are not going to see an increase in performance. For this Trinity changes the front Variator, uses different weights, a wider Kevlar belt with a Delta Performance rear clutch.

While the motor was at Trinity, they also remove the oil injection and the starter motor, no sense in carrying around added weight. With the motor back in our hands, we bolted it into our Alpha Sport 90. The carb, pipe, and air-filter installed with ease. This brings us to the one thing we did not like about this kit, the air-filter sits right next to the front tire and if riding in adverse conditions, every time you turn to the left, the tire throws debris up on the filter. Since then we have fabricated a shield to protect the air-filter from further debris.

Without the electric start, the motor now has to be kick started. After 3 kicks the motor fired right up. Fortunately for us this carb was jetted spot on and we only had to adjust the idle screw in 1/4 turn. Since this was a new piston, we put the motor through a couple of heat cycles at idle letting it cool completely each time before we restarted the motor. By this time we were all chomping at the bit to see how these few simple bolt-on items would help with the overall performance. After a couple of slow trips around the track to make sure everything were working properly, we proceeded to put it through its paces. Right away, I decided to pin the throttle to see what kind of response it had. To my surprise, I was fighting to try and find the rear brake to bring the front end back down. This thing just hooked up and launched the front end skyward, mine you, we are talking about a 200lb adult and not a 70lb kid. Once we regained control, we opened it up, and let me tell you, this thing flies for a 90cc machine. Every adult that threw a leg over this machine was thoroughly impressed by its performance. They could not get over how responsive the motor and clutch system were.

After the kids got all the adults off, it was there turn to play. Once they had sufficient time riding around getting used to the machines new power, we turned them loose in the sand pit to see how much fun they could have. Hills that gave the stock machines problems before, now were just little obstacles. Words such as awesome, cool, great and it’s a blast were used quite frequently to describe this machine.

The final test was speed. After many searches on various websites that post Drag Race results, we found that most of these 90cc motors that are modded run in the low to mid 7 second range. We figured if we could hit that mark we would be happy. Gears were not available for the Alpha Sport so we decided to change tires size to simulate a change in gearing.


300 Foot Drag 928kb
60 Foot Drag 350kb

1st up was 18" Turf Tamers. In 300' the average time of 5 runs was 6.884 seconds with a 60' average of 2.197 seconds. Next we proceeded to the stock tires which are also supposed to be 18" but they actually measured 19" after we measured them. With these tires on the average time in 300' was 6.726 seconds with a 60' of 2.209 seconds. Now we bolted on a set of 21" knobbies. Our test riders commented that they liked the feel of these tires the best. The times also reflected what they told us with an average of 6.635 seconds with a 60' average of 2.260 seconds. Our last tire that we bolted on was 22" 4-Snows. Although this is over kill for a quad this size we were curious to see how the motor and clutch would respond to these tires without any changes. To our surprise they really didn't fair too badly. The 300ft average was 6.795 seconds. Once the 300' times started going down we decided that was the maximum limit that this motor could pull with the current setup.

We did have an opportunity to get this motor to the last race of the year. In live competition this motor was able to defeat the NY State 90cc Mod Class Champion by making 2 consecutive runs of 6.715 seconds backed up by a 6.716 run in very poor track conditions. By the end of the day it had turned faster times then stock Raptors and DS650s.

In conclusion we are very thrilled with how this motor prepped by Trinity performed. It did everything it was supposed to and more. The best part is that there is more to get out of this motor in the future if needed. For more details on this motor Trinity can be contacted at:

Trinity Racing
3035 E. La Mesa
Anaheim, CA 92806
For Ordering: 1-877-FASTOYS
Information: (714) 632-3434
Fax: (714) 632-8484

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