This reference is designed to help service technicians find and eliminate problems associated with fun karts and mini bikes. It is not meant to be used as a service manual. To successfully use this guide: first, identify the major problem with the unit in question. Second, locate the most appropriate section below. Third, find the major problem in the section and check all possible causes listed. Possible causes are listed in order of probability; the most likely causes are listed first.
WARNING: Assembly, maintenance, and/or repair of the kart or mini bike should only be performed by persons of sufficient mechanical skill, experience, and judgement (such as outdoor power equipment or small engine dealers) so that no unsafe conditions or modifications are made.
Erratic engagement is most often caused by the driver clutch that is mounted on the engine crankshaft. The flyweights in the clutch are sticking or the movable sheave is binding on the hub. Knowing how they work may help you determine why yours doesn't. As engine rpm increases, the flyweights push against the outer drum and force the movable sheave (pulley face) toward the engine causing the belt to travel at a greater circumference around the driver clutch. This action in turn causes the belt to force open the driven pulley, allowing the belt to travel at a lesser circumference around the driven pulley.
As engine rpm decreases, the spring in the driven pulley closes the pulley forcing the belt to a greater circumference. This action overcomes the force of the flyweights against the movable sheave and causes the driver clutch pulley to open, allowing the belt to travel a lesser circumference around the driver clutch.
When the engine is at idle, the driver clutch pulley should not engage the sides of the belt. The belt should be loose in the pulley and resting on the bronze bushing around the hub. The bronze bushing serves to protect the belt from rubbing against the spinning hub at idle and also to support a portion of the movable sheave as the sheave moves toward the engine during engagement.
The movable sheave must be able to slide freely on the splined hub without binding. Disassemble the driver clutch and clean away any dirt or lubricant residue using an automotive parts cleaning solvent. Do not use a petroleum based lubricant inside the driver clutch or between the hub and movable sheave. Use a dry, molybdenum based lubricant such as Comet GP-370. The extreme heat and pressure inside the driver clutch chars most petroleum based lubricants. Petroleum based lube also collects dirt which causes increased wear. Graphite lube is better than petroleum lube, but it also eventually leaves a residue that builds up on the parts, causing them to bind and require more frequent cleaning. Experience has taught us that the Comet GP-370 lubricant (or equivalent ) works best.
Problem |
Cause |
Solution |
| Belt is worn thin in just one portion | Excessive slipping of Drive Clutch Pulley caused by:
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| Drive Clutch turns while engine idles |
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| Belt is worn "Cup" shaped (concave) on sides | Too much run out on drive clutch pulley |
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| Belt Disintegration | Excessive belt speed | Reduce R.P.M. at high speed |
| Belt "Roll Over" at high speed |
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| Cord breakage on belt edge |
|
Align system |
| Cracking between cogs on belt | Belt is wearing out | Replace belt |
| Broken or torn cogs, compression section broken/torn |
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| Belt worn uneven on one side |
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| Belt has glazed or baked appearance | Excessive slippage is caused by:
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| Top width of belt worn too much |
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