This article begins the first of series of articles dedicated to exploring the performance potential of the 50 & 90cc Asian mini or youth ATV. Whether your intention is to keep up with your young rider's increasing growth and riding ability, or to build a competition machine, the kids' section of SportQuad.com has been hard at work researching the options available to these little machines. Although the modifications discussed are targeted at the smaller 50cc market, almost all of these pieces can be applied to the 90 as well with very favorable results. These performance upgrades will work on nearly all of these Asian lookalikes- including Alphasports, Kasea, Polaris, DRR, T-rex, Dinli, Eton, etc.

We've visited race tracks and trade shows, talked to all the major high performance parts suppliers, queried the racers (and their dads), perused the discussion forums, and finally, tested the components ourselves. One thing is for certain (CPSC cover your ears), these machines have a tremendous amount of potential left in them. To best illustrate this point, I can personally offer the testimonial that by adding the pieces described in Stage 1 & 2, my two recreational racer sons were able to finish 1-2 in their first AMA motocross.

Aluminum air-cleaner shield installed over a K&N air filter.

Anyone who has experience with these machines will quickly tell you that the easiest, and most inexpensive modification you can make is to replace the stock airbox. Not only is the airbox restrictive, but most have a pretty lousy fit. This means that not only will dirt and water enter the airbox from the snorkel or inlet pipe, but also between the rubber elbow boot between the airbox and carb. Dirt can enter the carburetor and starve off critical air and fuel passages and cause driveability issues... or worse, cause piston scuffing and ring sticking. And as far as performance goes, since power is directly proportional to airflow, decreasing the resistance to airflow through the air-cleaner translates directly into more power. 

The simplest solution to this is to remove the entire air-cleaner assembly up to the carb and replace it with a K&N or Uni-filter. This dramatically improves the ability of the engine to breathe and seals off any potential for dirt infiltration between sealing surfaces. Carburetor main jetting has to be changed to compensate for the lower restriction air-cleaner, otherwise the engine will bog (lean). The stock main jet size for the 50 is a #75, which technically speaking means the orifice will pass 75cc of fuel per minute under certain standard conditions. Although factory jets (through Polaris) are available up to even #95, an even larger jet will be required to provide optimum full speed fuel mixture (around 12:1 air to fuel). Several shops offer larger non-stock size jets, but it's relatively easy to modify your own using a "number" drill set. With a K&N filter, the engine seems to want about a #61 drill diameter, which corresponds to around a #100 jet.

Speed vs Power plots for stock and modified configurations on an Alpha 50.  Click to enlarge.

Idle mixture wasn't affected, nor was the needle height optimized. However, with this simple modification, nearly a full horsepower improvement was affected (see graph). The highest gain was in the 10 mph range, where most riding is done anyways. 

The downside to replacing the stock airbox is that it places the open style aftermarket filter vulnerably in the wake of the left front tire. Unprotected, the filter will quickly pack with dirt, mud, and/or water and any initial performance gain will be substantially mitigated. To the rescue is an innovative shield to fend off debris from the spinning and splashing tire that bolts in place of the stock plastic airbox. Although appearing restrictive, the "proof in the pudding" indicates no power compromise with the shield installed (air is drawn from the Z in front, and also from the carb side).

The whole kit is available via Advanced Sleeve. Call them at 440-354-3440 to order one for yourself. Next month we'll venture into the arena of exhaust systems and clutching. Stay tuned for the next installment.

Where to get your parts- K&N air-cleaner-

• available via any K&N or Parts Unlimited dealer, or call 800-314-4729 to find a dealer
• part number- 62-1430 (or old# R1140)

• Offered as a kit including jet, K&N filter, and shield 
  from Advanced Sleeve, 440-354-3440

• Hetrick Racing, in PA, 814-676-0477
• MiniATVparts.com, in GA, 678-873-6253
• Trinity Racing, in CA, 877-FASTOYS
• WRH Racing, in AL, 251-675-9906