I have written several comments on this topic in the past, but I think it bears repeating, because there are two possible reasons why your clutch is smoking. Usually I talk about one of the most likely reasons, but in this article let’s talk about the two possible causes why your clutch is fuming on your kart.
First, you need a fundamental understanding of karts.. The driveline generally consists of a clutch driver and driven shaft sprocket. The drive axle sprocket mounts directly to the rear driver’s axle which turns the drive wheels. This is a one-step system or a single-rate system.
The centrifugal clutch used in most go-karts uses weights that are internally mounted on the clutch that trigger and press against the clutch bell. The bell housing then in turn drives the sprocket that drives the sprocket teeth.
The typical clutch has 10 to 12 sprocket teeth.. As a general rule of thumb, any clutch that has more than 10 to 12 sprocket teeth will give driveline problems. Problems like in the smoking clutch.
Coupling of the weights to the clutch bell housing occurs at certain rpm. Typically these rpm’s are around 1800-2000 rpm. The engine needs to fly through this level of rpm and get the clutch pack to stick and eventually engage the walls of the clutch bell. The smoky look occurs when the clutch engages but does not fully grip. If prolonged engagement happens for too long, the clutch will start to smoke and eventually damage it to where the weights will just slip and maybe even crack and break.
As I said at the beginning of the article, the long-term commitment occurs due to two possible reasons:
1.) The engine is not powerful enough to pass the participation stage.
2.) The rpm of the clutch weight is not high enough.
The engine is not powerful quite typically it is the result of a mismatch in the rear drive wheel ratios. So the real reason is that the ratio is not pronounced enough and therefore the engine fumes the clutch.
(Another possible problem can occur and that is if the clutch is made to engage at less rpm than the engine can grip, the engine may not have enough power and the engine may suddenly (more violently) jerk and stall. It is not uncommon for the engine to be so overpowered that it spins backwards momentarily).
The second way the clutch will smoke is if the clutch rpm never reaches clutch speed, or is close to clutch speed, but not high enough above clutch speed to get a lockout. This will fume the clutch and is common with mismatched intermediate shaft systems.
The remedy for the first clutch smoke. The problem is altering the driveline to make the overall ratio more pronounced. The simple method is to increase the diameter of the rear sprocket. Programs have been written that will estimate whether or not the clutch will smoke, they are usually found on web pages or are available for purchase through various web pages. Typically, what happens is that the horsepower ratio will simply not be possible using the simple system of a ratio. Therefore, it is necessary to add a jack axle to make the relationship even more pronounced. In other words, make it a two-proportion system.
This is where users installing intermediate shafts should be vigilant. Usually the clutch cannot be placed on the intermediate shaft driver, with a ratio in front of it. This will cause the clutch to rotate too slowly, even though the overall ratio is correct. Therefore, the clutch engagement rpm must be taken into account; otherwise, the clutch will smoke at the secondary output shaft mounting position.
The bottom line is if clutch it is not activated because there is too little horsepower or the clutch speed is too slow, then it is necessary to change the system by modifying the ratios, either behind the clutch or in front of the clutch.