MaxTorque clutch tuning mods

I wanted to share some notes on tuning the MaxTorque "SS" six shoe clutch. This clutch was given to me for free, so I'm investing time and a little bit of money to make it engage as smoothly as possible. I read up on clutch tuning about a year ago, but haven't had enough money to buy all the necessary parts to tune this clutch. Before I get too deep into this, let me add that at this point I've already got the clutch engaging pretty smoothly, and I'll share what I've done so far to make it run smoother. The rest of the mods I'll be performing are just to make it engage better at lower rpm's, because it does slip a little when going very slow or giving it short bursts of throttle, such as when I need to stop and speed up quickly.
So the first mod that I made was to change the spring. The stock spring is silver and engages at about 2200 rpms with the stock shoes. There is a green spring that will engage around 2500 rpms with the stock shoes for those who may be interested in trying it. I did not use the green spring. I used the black spring, which engages at 3100 rpm's with the stock shoes. Changing the spring helped a good bit at first, but eventually the clutch began to chatter again badly.
Next, I began to notice quite a bit of play in the drum. Upon disassembling the clutch to clean and inspect it, I noticed that there is a sizable gap between the clutch shaft and the bushing. There was a thin fiber washer between the two, but it was not thick enough to take up the entire space. I went to Home Depot and got a thick fiber washer. I cannot remember the thickness, but it was the only fiber washer they had that was the same inner diameter as the fiber washer that had been in the clutch to begin with. I took the original washer with me to match up the diameter. The thicker fiber washer cost about 60 cents. It takes up the entire space between the clutch shaft and the bushing. Eliminating the play in the drum helped the clutch to balance itself better when engaging.
The next modification I made was to replace the bushing. This is not a mandatory step for tuning, especially if the clutch is new. The replacement bushing is exactly the same as the original bushing. I replaced mine because they do get worn down after awhile, and I'd been using the clutch for about a year. I've no idea what kind of use it went through before I got it. The bushing was 3.50 plus 7 flat rate shipping. Upon replacing the bushing, I began to lubricate the clutch with grease. Motor oil is generally recommended, but it slings all over the place and can get inside the drum, which is bad. I disassemble the clutch and use a q-tip to grease the inside of the bushing, and I also grease the clutch shaft at the same time. This has had a huge effect on the smoothness of engagement. I take it apart once a week or every two weeks depending on how much I ride. I also grease the crankshaft to make it easier to get the clutch on and off. It used to get stuck so bad I'd need a hammer and something to pry it off with. Now it slides right off.
I have also ordered heavier shoes for my clutch. A lot of people will not agree with this, but during my research on clutch tuning, I read that the best way to get smooth engagement across the powerband is with a heavy spring and heavy shoes. It doesn't make sense to a lot of people, because it goes against popular theory. So I expect I will get some negatory comments here about it. But the shoes have already been ordered. The stock shoes weigh 46 grams. The wedge shoes, as they are called, weigh 62 grams each. Lighter shoes provide a later engagement, but they dont lock as quickly even when the clutch starts to engage. Heavy shoes provide an earlier engagement as they fly out and catch quicker. I'm expecting that with the heavy spring and heavy shoes, my clutch should engage a little sooner but lock very quickly. I haven't received the shoes yet, as I just ordered them today. When I install and test them, I will update this thread. Fyi, you can try to order the wedge shoes from affordable go karts if they have them in stock, but I ordered mine from comet kart sales and the shipping was $5 cheaper than agk.
So that's all I have to share for the moment on this.

I will try to remember to take a pic of the fiber washer I installed when I have the clutch apart again. But pics aren't going to show any other differences, like the new bushing or the difference between the new shoes and the old, and pics aren't going to prove that these mods actually work. Neither would a video. You'll just have to decide if you're willing to take my word or not.

The wedge shoes are on their way! I will report back with pics and a report of how the clutch runs once I get the new shoes installed in a day or two. The guy said they would probably be here tomorrow, but I have to work so I probably won't get to it till Wednesday, when I have off again.

I got the wedge shoes earlier today and have already installed them. The install went surprisingly smooth with the heavy spring. Getting the heavy spring in was always a pita with the regular shoes. But it went in just fine with the wedge shoes. Unfortunately it is raining, so I may not be able to test the clutch till tomorrow, as I don't expect the roads to dry enough for a safe test ride today. But I will definitely report back as soon as I do test it.

Well, the storm has passed and the sun is back out, so it might dry up enough for a test ride. I have to return a movie I rented, so if it dries up enough to go do that, it's a perfect opportunity to test the clutch today. In the meantime, I've got a few other adjustments I'd like to make, so we'll see if it dries up by the time I finish that.

So after installing all 6 heavy shoes, the clutch was engaging way too early and chattering and slipping badly. So what I decided to do was mix the shoes. Shoes can be mixed, as long as it is done consistently. So I alternated, every other shoe heavy, every other shoe regular.

This changed the engagement from around 2k with all heavy shoes to about 2500 or 2600 rpms. The engine I'm using makes max torque at 2500 rpms, so the engine should carry me up hills as long as the rpms don't drop below the engagement speed. This also sets the clutch at optimal engagement for pedal assistance. I tested it, and it will engage on its own just fine, but I will accelerate quicker by pedal assisting. So it's almost the same to me as having a manual clutch, because it's not engaging too high to pedal assist, which is great for me.

I've also switched to a different grease. The yellow grease I was using was slinging into my drum and causing problems. I had a small amount of red grease which is tackier, and I used that so it won't sling into my drum. When I get paid Friday, I'm going to go to the auto parts store and get a can of Red'n'Tacky grease and start using that. I'm throwing the yellow grease in the trash, as it's almost gone anyway and I have no more use for it.

So there you have it. As far as I'm concerned, the best way to tune a maxtorque clutch is at optimal engagement for pedal assistance. Too early and it will slip, too late and you may not be able to pedal assist. I have pretty low pedal gearing. I could go taller, but it would be harder to assist going up hill, or if I ran out of gas. It's a single speed, and it's a heavy bike with a heavy rider, not designed to be pedaled any distance. So I have my pedal gearing set 36t chainring and 23t rear cog.

You must be using the silver spring then. I'm using the black spring, and going heavy/light, heavy/light I'm engaging around 2500. 1600 would be way too early for an engine that only makes 2.8 ft/lbs of torque and maxes out at 5k. Talking about my 98cc flathead. As far as gearing goes, I'm not willing to make any changes at this time. I'm geared at 12.4:1 on 26" tires, and my top speed is about 30-32. I simply don't want to go any slower. I've actually figured out that most of my clutch problems are related to an inconsistent idle. The compression release on my engine is a copy of the Briggs ez-spin, a permanent bump on the intake lobe of the camshaft which keeps the intake valve open through most of the compression stroke, which causes a very inconsistent idle. In order to keep the engine from dying at idle, I have to turn the idle up higher than where the clutch engages. This means I am slipping the clutch at idle, and it's overheating. I plan on removing the compression release tomorrow, so hopefully this problem goes away after that. I believe it should.

Finally figured out what the real problem was. A little background first. A couple days ago, I serviced my front drum brake. The shoes were glazed, and the drum was a little rusted. Mind you, it was used when I got it. So, I lightly sanded the drum and the brake shoes with 100 grit sand paper. The brake worked much better after I did this. Now, a centrifugal clutch is essentially the same thing as a drum brake. So it finally dawned on me, if a drum brake needs service from time to time, a clutch probably does too. So I disassembled my clutch and went to work. First I sanded the shoes until all shininess and discoloration were gone or as much as I could get. Then I set to work on the drum. I first swabbed it with alcohol until all grease and grime was gone, and then I sanded the drum until my hands hurt too much. Most of the burnt part is gone. A small black mark remains that spans roughly half the circumference of the drum, but my hands hurt too much to keep going. I swabbed with alcohol again, and re-assembled my clutch, using Lucas Red-n-tacky grease sparingly on the clutch shaft and bushing. Also, I decided to go back to all regular shoes to see if it was really just that the clutch needed servicing, and I took it for a test drive. The clutch engages very smoothly, and pedal assisting helps with acceleration. This is the smoothest my clutch has engaged in a long time, maybe ever. So long story short, the real trick to keeping a clutch running smoothly is to service and maintain it properly.

I use grease on my shaft and bushing, lasts longer, slings less. I'm not changing my gearing till I switch to 24" wheels.

The black stuff was mostly burnt on, caked on grease because I had been using a cheap hi-temp grease. Now that I've switched to tacky red grease, it shouldn't sling at all especially if I use it sparingly. I would much rather disassemble the clutch once a week and lube it properly with grease than just dribble some motor oil in every once in awhile. While I have it apart, I can swab the shoes and the drum with alcohol, so if any grease does happen to sling into the drum, i'll get it before it burns and cakes on. If I find excessive blackness starting to show up, I'll sand again. Disassembling the clutch definitely gives me the opportunity to inspect it and service it if necessary anyway.