I have written several commentaries on this subject in the past, but I think it warrants rehashing, because there are two possible reasons why your clutch is smoking. I usually discuss one most likely reason, but in this article let’s talk about the two possible causes of why your clutch is smoking on your go kart.
First the fundamental understanding of go karts is needed. The drive line typically consists of a clutch driver and the driven axel sprocket. The driven axel sprocket is mounted directly to the rear driver axel which turns the drive wheels. This is a one step system, or a one ratio system.
The centrifugal clutch which is used on most go karts, uses weights that are mounted internally in the clutch that fling out and press against the clutch bell housing. The bell housing then in turn moves the sprocket driving sprocket teeth.
The typical clutch has 10 to 12 sprocket teeth. As a rule of thumb any clutch that has more than 10 to 12 sprocket teeth is going to give trouble to the drive line. Trouble as in smoking clutch.
The engagement of the weights to clutch bell housing occurs at a certain rpm. Typically this rpm is around 1800 to 2000 rpm. The engine needs to blast through this level of rpm and get the clutch pack to stick and finally engage to the walls of the clutch bell. The smoking aspect occurs when the clutch is engaging but is not fully grabbing. If the prolonged engagement occurs for too long, the clutch will start to smoke and eventually damage it to where the weights will only slip and perhaps even crack and break apart.
As I stated at the start of the article, the prolonged engagement occurs because of two possible reasons:
1.) The engine is not powerful enough to get past the engagement stage
2.) The clutch weight rpm is not high enough.
The engine not being powerful enough typically is the result of a mismatch in ratios to the rear drive wheels. So the real reason is that the ratio is not steep enough, and therefore the engine smokes the clutch.
(Another possible issue can occur and that is if the clutch is made to engage at lower rpm than the engine can grab at, the engine may not have enough power, and the engine will suddenly (more like violently) shudder and stop. It is not uncommon for the engine to be so overpowered that it rotates backwards momentarily.)
The second way the clutch will smoke is if the clutch rpm never reaches engagement speed, or it is in the neighborhood of engagement speed, but is not high enough above the engagement speed to get a lock. This will smoke the clutch and is prevalent in mismatched jackshaft systems.
The remedy for the first clutch smoking problem, is to alter the drive line so that the overall ratio is steeper. The simple method is to increase the rear sprocket diameter. Programs have been written that will estimate if you clutch will smoke or not, they typically are found on web pages or are available for purchase through various web pages. Typically what occurs is that the hp-ratio just will not be possible using the simple one ratio system. So a jack shaft needs to be added to make the ratio even steeper. In other words, making it a two ratio system.
This is where guys who install jackshafts need to be aware. The clutch typically cannot be put on the driver of the jackshaft, with a ratio in front of it. This will make the clutch rotate too slowly, even though the overall ratio is correct. So the clutch engagement rpm needs to be taken into account otherwise the clutch will smoke on the secondary jackshaft mounting position.
The bottom line is if clutch is not engaging because of either too little hp, or too slow of a clutch speed then the system need to be changed by altering the ratios either behind the clutch or in front of the clutch.
Why My Clutch Is Smoking On My Go Kart by Robert Gamble