The following is a cut-and-paste from the Venom Performance Products catalog. It is the best concise clutch tuning tips that I have seen. If I was going to write my own clutching tips they would look almost identical. Of course the Bible that many people use is the Aaen Clutch Tuning Handbook. I have owned my copy for almost 30 years.
CLUTCHING TROUBLESHOOTING TIPS
You must make sure EVERY part of your drivetrain is working before you start tuning on your clutches. The first things to check before you go buy clutch tuning components are:
• Is your motor running like it should? If you cannot pull stock clutching, you have an issue somewhere.
• Do you have a fresh, broken-in belt? Even though your belt may not be shot, it could be worn to the point where you don’t get the same performance.
• How are your motor mounts? A motor that moves in the chassis under power will not keep clutch alignment and calibrations go out the window.
- Are your clutches in alignment? Check your alignment with an alignment bar.
- Do you have sufficient traction? A studded track is a must for flatlanders if you want consistent results.
Once you have all of these things in line, here are some tips to get your clutching spot on. The first and most important key to getting good clutching is to have good data. This means a recording tachometer or other playback device. In my years in this business I have learned that people cannot watch a tach and give good feedback. It’s also dangerous. Max recall on a stock tach is meaningless, also. Once you have good data, these are some of the things that can happen on full throttle pulls from a dead stop: (RPM on the left scale, and MPH on the bottom scale).
• Ideal- The ideal shift curve climbs to your rpm of max horsepower quickly and stays there throughout. This graph assumes 8200 is the ideal RPM.
• Low- If your RPM is low throughout the shift curve, you are over-clutched. You need to drop gram weight in the drive or drop helix angle (initial and final) in the driven. Going up on spring rates in both the drive and driven clutches will also raise operating RPM.
• High- If your RPM is high throughout the shift curve, you are under-clutched. You need to raise gram weight in the drive or raise helix angle (initial and final) in the driven. Going down on spring rates in both the drive and driven clutches will also lower operating RPM.
• Climb- If your shift curve climbs then you have too much helix at the beginning and/or not enough initial driven clutch spring.If you are using adjustable shift weights, you may have too much weight in the heal of the weight (nearest the pin).
• Fall- If your shift curve drops then you have too much helix angle at the finish, too much gram weight in the drive, and/or too much initial driven clutch spring. If you are using adjustable shift weights, you might have too much weight in the tip of the weight (farthest from the pin.)
• Overflash- This occurs when the drive clutch has complete traction on the belt, but the driven clutch does not let it shift soon enough. More initial helix angle and dropping driven spring preload will fix this.
• Slip- This looks like overflash, but the motor is bouncing off the rev limiter at the start. This is caused by the drive clutch not getting full traction on the belt. This can be caused by too much gearing, not enough initial helix angle, too hard of a belt compound, too much drive clutch spring preload, and not enough heal weight in the drive clutch weights.
• Bog- While similar to climb, a bog is more pronounced and can indicate a belt that is shot, a motor problem, or a broken motor mount. A bog that bad generally is not due to clutch tuning.
