KT100: Clutches...or Direct Drive?

I didn’t see anything on this topic already so I’m starting a new thread. Hopefully this isn’t redundant and I just missed something. In 2018, I will be racing a KT100 out here in NorCal. Here, we have a rules package that is meant to be inclusive to get as many 100cc engines as possible off those garage shelves and onto the track. The rules allow for 4 hole can or a variety of pipes, such as RLV3 or the DD87 Direct Drive pipe. It also allows an open drive method. When I raced the KT100 in 2005, I didn’t have much choice. The kart I bought came with a 3 disc wet Hortsman clutch and that’s just what we ran. This time around, though, I currently have a 2 disc dry (I believe Patriot) currently on the kart, but I also have a 3 disc wet L&T and a 3 disc wet Hortsman. I’ve done lots of looking online and everyone has an opinion on the matter, but I trust these forums so any thoughts would be great.

What I’m interested about, though, is the direct drive sprocket I found. All of my clutches are 11 tooth, which require a large rear gear. But I found a 10 tooth direct drive sprocket amongst the parts I got with the kart. I know it would be a very different beast to drive without a clutch, which is what I’m used to, but I’m interested in trying it. So, I come to you guys for advice.

What are the benefits and downsides to direct drive?
What are tips for a trying it for the first time?
Same gear ratio as if with a clutch?

Thanks KP!

You’re going to be (over)revving the motor more with direct drive. Because you don’t have the clutch slipping and keeping the motor closer to it’s powerband out of tighter turns. With DD you might find (for example) your RPM’s dropping to 8800 at the tightest turn, whereas with the clutch, as soon as you get on the gas, it spins up to the engagement point around 11K

Your gearing will likely be shorter with DD, but it does vary with the track. Consequently, you’ll find yourself spinning more RPM on the longer straights which is harder on moving parts. You can run the same ratio as the clutch setup if you like to be safe.

Try DD, it’s a lot of fun.

Thanks for the info! I think I will give it a try. Any good tips/videos on starting a DD for a newb to it?

Before The KA100 came into the sport in Aus we ran our version of the kt 100. Consensus here was that the clutch sapped power from the engine and direct drive was faster.
I don’t know if that is 100% accurate or what sort of clutch was on offer, but I never raced against any KT’s with clutches even though it was an option, if that is any indication.
We used to have also a 9 tooth front sprocket, so I could get into the 70’s in rear sprocket size, something i wish i could do with the KA.
Have a crack at DD an see how you go. It is a total different way to drive, because you have to keep in the back of your mind that there is no second chances. I would say it will improve your driving if nothing else.

@Mynameismcgyver tested DD Yamaha Supercan a couple years ago in practice before the officials gave him sh*t for it and made him put a clutch on.

Any valuable information from that quick session or two Mike?

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Anyone know where I could find a direct drive sprocket for the KT100? It’s always interested me but I’ve never done it.

Found it here for $20 - http://www.out2win.com/catalog/sprkt_eng.html

A direct drive Yamaha with a ‘Formula Y’ pipe on it is actually pretty quick. Close-ish to a KPV with a 3 pipe and heavier driver.

Thanks for the input guys. I think I will give DD a drive at some point; sounds like a blast and a fun, new challenge. Tomorrow, though, I’ll be with what I have been practicing with since it’ll hopefully be a big (relatively speaking for an off season meet up) turnout for our 100cc get-together. I don’t think learning how to push start a DD with a whole bunch of people around is the smartest idea. I want to perfect it and show up to the first race weekend able to do it like a pro. They need to fear me! Haha joking aside, I don’t want to cause any chaos when tomorrow is about fun and getting as many 100cc 2-strokes out there as we can.


Well, that didn’t go as planned. They make it look so easy in the videos. I ended up getting to the track yesterday, not Saturday, because the wind was terrible on Saturday. So, since there wasn’t a crowd, I figured I’d give it a crack. That thing was a pain to try and get started. It was fun to drive the few laps I was able to turn, but with my home track having a couple very tight turns combined with the nuisance of trying to get it started, I think I’ll be going back to a clutch set up.

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So I finally had some time today to change from the DD back to the dry clutch I had originally on the kart and…I can’t get the dang DD sprocket off to save my life. HELP! I do not have the removal tool (probably should have thought that through before I put the DD on), and I’m not wanting to spend $75 and waiting for shipping from Australia to remove the dang thing once. KP, please help.

Sorry dude, you will need the removal tool.

You can get away with a 3 prong puller, If you are lucky and very careful. With a 3 prong puller you risk damaging your crankshaft.

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