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FUN TIMES

HIGH PERFORMANCE MACHINES — Fun Kart Series Part 3
By Paul Dilger – Courtesy of OPE Magazine

The particular fun kart that I received for evaluation is the Carter Brothers’ Model 2900-4015. The kart arrived in a box that was metal-strapped to a large wood pallet. It took about five minutes to remove the internal and external strapping and the box that housed the partially assembled kart. The average time it takes for a dealer’s technician to assemble a kart using air tools is about 30 minutes.

The entry-level fun karts that I featured last month have a centrifugal clutch that couples the engine crankshaft to the chain drive sprocket to achieve forward motion. As we progress to more expensive karts with more accessories to choose from, they use a torque converter system that merely tightens up a drive belt as the engine accelerates. I will describe this system in detail later, but briefly mention it here for the following reason.

Kart manufacturers positively state that you must have an experienced operator in the driver’s seat when the engine is started in any kart of any size. However, this presents a challenge for the technician who is working alone and wants to check the idle speed of either an electric start or manual (rope) start kart. Therefore, manufacturers recommend that the kart be placed against an immovable object and then started. This lessens the likelihood of unwanted engagement of the drive system. I wanted to be able to look things over with the engine running and without being in the driver’s seat, so after blocking the kart behind an immovable object, I placed two jack stands under the engine frame, thus lifting the tires off the ground, then started it. I mention this for safety purposes because I believe any technician working on a kart should always place stands under the kart frame if the engine is going to be started.

After first cruising slowly around the farm for a half-hour, my oldest grandson, Travis, took the model 2900-4015 out to the test track that we had prepared for this article. The course runs about a half-mile through hills, gullies and flat land with both wide and sharp turns. Any object that might pose a safety hazard was removed from both the track and the sidelines before we ran the course.

The 2900-4015 kart has a 9-horsepower, OHV Tecumseh engine. This is a good balance of engine horsepower-to-weight ratio for a kart carrying two people. There were several tests I felt the kart and engine should pass. First, because of its lower center of gravity, the kart should out-handle a quad on turns. Second, it should be able to brake adequately on a steep, downhill drop-off. Third, it should have enough power to break loose the rear-drive tires to power around turns tighter than the steering radius. Fourth, I felt it should feel; stable at competitive speeds. Fifth, it should be somewhat comfortable on a track that has a “washboard” texture.

I am pleased to report that the kart met all of my expectations! One special test I devised was to stop while going uphill in the middle of a 40-foot dirt slope, inclined at 45 degrees, and the restart from a dead stop with two riders in the kart. This test simulates an over-load condition, and the kart easily accelerated up and over the top of the incline. Two other hill tests were performed to see how well the brakes would hold and my ability to back the kart down around curves without it getting away from me. In all the track tests I conducted, I pushed the kart to its limits, and it safely passed all of them. Keep in mind that spent a long time building a track for these tests, and I designed safety into every aspect of the course.

When you’re driving this kart, you won’t have any problem remembering who manufactured it. Carter has cut out its name on the dash. The dash stabilizes the steering column, as well as houses the safety start and run key, and the system electrical fuse. This 2900 model sports an entire electrical system that includes full lighting, a battery to power the starter motor, and an alternator to charge the battery. (Sorry, a CD player is not an option.) The large engine gives the driver manual choke control. The easy-to-read identification plate is located on the platform under the driver’s right leg.

Servicing the Tecumseh engine mounted on the Carter machine is simple because both the oil fill and gas caps are located on top of the engine and are easily accessible from the rear of the kart. The kart also has an anti-splash gas cap designed for operator safety. Fun karts are designed to run on dirt roads and trails that create lots of dust. Carter uses a large paper air filter with a foam band to pre-clean incoming air. The foam band, when properly oiled, is nothing more than a washable pre-cleaner. Maintenance directions for the foam pre-cleaner are covered in the operator’s manual.

The engine is equipped with a spark arrester within the muffler. In case you’re not aware, it is unlawful to operate gas engines in many areas of the US with out a spark arrester. In California, where I live, you are financially liable for any fire your vehicle might start if you do not have a spark arrester approved by the U.S. Forest Service. This includes both physical damage and the cost of putting out the fire. Spark arresters do require periodic service. They should be removed and cleaned when carbon particles accumulate. Don’t forget to use silicone grease on the screws to prevent them from rusting.

Carter’s 2900 model has both front and rear axle suspension systems. The front suspension system raises the body of the kart up to increase the ground clearance. The front wheel’s axle is welded at a right angle to the kingpin (bolt) knuckle bushing. The knuckle then rotates around the bolt that’s between the fingers of the mounting yoke. This entire assembly is tilted up and gives the wheel a few degrees of camber. Along with front toe-in, the camber greatly enhances the steering under rough, undulating conditions. The yoke is attached to two sets of strut arms that float up and down with road conditions. When the body of the kart floats up due to hitting a bump, the camber on the axle provides the maximum traction for steering by giving the center line of the tire the maximum possible traction. Steering is most sensitive when the kart bounces up because there is less down pressure on the front tires to achieve positive traction.

The spring on the shock has several functions. First, to push down on the front tires as the kart tends to go airborne. Second, to push down on the yoke/spindle assembly to support the weight of the kart. Upon inspection, you will see that if the shocks were removed, the body of the kart would fall to the ground. The spring tension on the shocks also provides different levels of driver comfort. The tension on the spring can be adjusted by lifting up on the shock and rotating the notched spring coupler. A full turn to the high setting would provide a stiffer ride or be used for heavier loads.

Because the steering column is on one side of the kart, the length of the tie rods from the steering column yoke to the wheels is different for each wheel. To improve steering control, Carter Brothers uses tie rods of equal length. To accomplish this, an axial pivot is added on the passenger side. To understand why this helps steering requires an understanding of vector analysis, which involves engineering math and vector physics.

The engine is mounted on a swing-arm suspension system. The engine sits on a frame that has a pivot attachment point in the center of the kart below the kart body. As with the front suspension, the rear frame suspension is suspended by an adjustable shock. Well-designed suspension karts use this three-point, swinging-arm suspension because it provides a differential movement of the rear axle and the kart body. For example, if the rear tires go over a 4-inch speed bump, the kart body only moves up half the distance when the pivot point is mounted midway on the kart body. This dramatically smoothes out the ride and enhances operator control.

There are several features to point out on the solid-drive. Upon inspection, you will see the drive chain coming down to a very large sprocket bolted to the axle. Using a small drive sprocket powered by the torque converter system, a large driven sprocket on the axle provides an increase in torque and a decrease in maximum speed. The large sprocket provides extra torque that gives the model 2900 outstanding acceleration and climbing power. Note: two axle support mounts come off the axle supports the engine frame assembly. Both mounts have pillow-block sealed bearings that do not require maintenance. On each side of the left-hand axle support mount are two band brakes.

The torque converter is not a fluid coupler like that found as part of an automobile transmission. The torque converter used on karts provides both variable speed and variable torque to the rear axle.

Maximum torque is achieved as idle when the engine pulley is as small as possible and the driven pulley is as large as possible. As the engine speed increases, the driven pulley opens up causing the belt to ride lower in its pulley groove and higher in the engine pulley groove. This effectively lowers the torque on the rear axle as tire speed increases. If the kart heads up a steep grade that slows down the engine, the driven pulley raises the belt in the groove to increase the torque, similar to down-shifting a transmission.

The kart industry is continuously improving and expanding its offerings. Carter Brothers newest model is the 1150-XTV with an 11-horsepower, 150-cc, motorcycle-type engine. The 1150-XTV is a symmetrically balanced kart with the driver sitting in the middle to provide more efficient weight transfer, plus more horsepower to push the limits of kart racing. It is also available in a two-seater model. Where the 2900 model is a two-seater for 12 year olds and older; the 1500-XTV is for ages 16 and up.

I would like to express my sincere thanks to Ryan Daugherty of Carter Brothers Manufacturing Company, Inc. for his time and expense in providing me with the materials for this article. You can write Carter Brothers at 1871 US Highway 231, Brundidge, AL 36010. Carter’s phone number is 334-735-2301. The company’s website is www.carterbro.com.

In my next article, I’ll cover how the torque converter pulleys change pitch with rpm when I feature the big XKT-710E from Manco. I’ll also discuss other accessories that are available on today’s fun karts.

ABOUT THE AUTHOR: Paul Dilger is a retired professor of agricultural engineering at Cal-Poly State University in California. He worked as a mechanic in the U.S. Army before attending college. After graduating from college, Dilger taught mechanics for 25 years. He is currently a private consultant helping companies develop quality service training programs. Visit Paul Dilger’s website at www.imslo.com.

Article is © June 2003 by Outdoor Power Equipment (OPE) magazine and used here with permission. OPE magazine is published monthly by Adams Business Media at 833 W. Jackson Blvd., 7th Floor, Chicago, IL 60607. For subscription information and requests, call Subscription Services at 847-647-7399.

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