Honda PA Drivetrain


The Hobbit clutch can take a very wide variety of scooter clutch springs, which allow you to adjust when the clutch engages the clutch bell and begins moving the bike. Ideally your bike will launch right into the powerband of your engine/exhaust setup. The stock springs are much too weak for even a stock cylinder with an aftermarket exhaust, and higher performance Hobbits greatly benefit from even stronger springs.

Clutch springs come in various strengths for a wide variety of scooters. The RPM ratings of springs are only meaningful when compared with the original bike and clutch they are designed for. Which means a Dio "1.5k" spring engages at 1.5k RPM over the stock Dio clutch. You cannot compare the strength of springs to each other unless they are designed for the same bike. Additionally the colors are essentially meaningless unless you know exactly what set the springs came from. Malossi changes the color designations for their springs between sets for apparently no good reason.

Installing clutch springs

A pair of beefy circlip pliers with interchangable arms are ideal to get the big boy springs in. Remember, leverage is your friend. For lesser springs use an awl/pick/flathead screwdriver. Just insert the springs in on one end and use leverage to slide them down into the other hole. Trust me, it's not that hard. I put on the highest spring rate Malossi MHR springs all by myself with a set of circlip pliers in about 5 minutes once I got the technique down. After bending about 5 different arms, too.

This youtube video shows you the idea: [1]

Varieties of clutch springs

Honda Dio Springs

Most people with mild builds choose to use Honda Dio springs, which can be found on eBay. They come in 1000, 1500, and 2000 RPM varieties.

Those springs when used on a Dio give a corresponding rpm increase over the standard clutch engagement, the numbers may not reflect the actual rpm increase when used on the pa50 though due to different clutch components.

Some reviews for those are below:

K & R Tech

I bought two sets off of ebay: one “rated” at 1000 RPM above the stock DIO engagement RPM; and another rated at 1500 PRM above stock.

In the past, I’ve also bought and tried out a set for a Piaggio on ebay (from Treats).

The weakest Piaggio set changed the RPM engagement quite a bit – some on this forum have shared that the change was too much – and went back to stock springs. My son’s ported PA50I Hobbit still uses the weakest Piaggio set, and I don’t find them that bad – they are actually a good set for his motor.

The 1000 RPM set of Honda DIO springs are stronger than stock, but weaker than that weakest Piaggio set. I put this set on my PA50II (stock cylinder with a Leo Vince) – I can’t say how much the RPM went up, but it is a good step in the right direction.

By comparing spring material outside diameter, the 1500 RPM Honda DIO set is close to the Piaggio set – meaning that the step change may be too high for some.

The springs are pretty cheap, so I recommend buying both a 1000 RPM set and a 1500 RPM set. I wouldn’t dare try the 2000 RPM set – based on a comparison (and my experience) with Piaggio springs.

Anyway – here’s my own summary/suggestions: stock cylinder with aftermarket pipe – I’d lean to the 1500 RPM set; 70cc cylinder – I’d lean to the 1000 RPM set. My thought is that those riders with 70cc cylinders have more low end torque, and by the time the 1500 RPM set engages (or the lightest Piaggio set), there's too much power available. In contrast, those of us with 50cc cylinders (either stock or ported with aftermarket pipes), we can benefit from the "lost low end" by using springs that engage later. Buy both a try them out.

Getting them on can be a pain – especially the thicker springs – but that’s a story for another day.

J Campbell

Just installed and ran my 1000k springs I just bought. I thought they seemed a bit too stiff, but I went ahead and mounted them up anyway…


My bike is sooooo much better off the line! The engine revs up a bit before the clutches engage, and then BAM! 40-45mph stupidly fast… Topping out around 55. It actually picks up the front tire a bit if I try… wow!

Thanks so much for the head’s up on this.

This was the missing ingredient for my Hobbit. The bike is worlds better.

Malossi Springs

The Dio springs found on eBay are very very mild when compared with any Malossi springs for scooters, which can be found on treats and 77 and scooter shops. However, different Malossi springs are made for different bikes with different size clutches so experimentation is the name of the game. This PDF provides some guidance. Remember that these numbers are only meaningful for the original bikes so a "10,000" RPM clutch spring doesn't mean you rev to 10,000 on your Hobbit before you blast off into wheelie death. Additionally a spring for a certain RPM for one set will not be the same spring even if it has the same RPM designation from another set. Some good matches are the Malossi 29 9605 set for a milder kitted setup or the Malossi 29 8747 set for crazy builds that need a good launch to avoid dropping out of your powerband.

Starter Clutch

(Pasted from a post in this thread)

The clutch bell and variator assembly spins on bearings at the end of the crank. Moving the rear wheel rotates the variator and clutch bell on the crank, but because it spins on a bearing this does not make the engine turn over, and therefore not start. The starter clutch is attached to the inside of the clutch bell and has very very light springs that cause the arms to spin out very quickly when the bike is pedaled or push started (with the drive engaged, of course). The arms grab the outer wall of the clutch, which is attached to the crank via the taper fit, and the engine begins to turn over, which lets you get it started. Once the bike is started and at very low revolutions, the starter clutch disengages from the clutch and the clutch bell/variator assembly sits at rest, with the crank rotating at the idle speed, spinning the clutch but nowhere near the revolutions required to make it engage the clutch bell.

When you throttle on the crank increases RPM, the clutch spins up with it (since it is attached to it via the taper fit) and the arms begin to spin out due to the spinning force. The clutch springs provide resistance against this, but once the resistance is overcome at a certain RPM, the clutch arms engage the inside of the clutch bell, which then begins providing power to the rear wheel, making you go forward. When you throttle off, the bike spins down, and the clutch disengages from the inside of the clutch bell at whatever RPM the springs draw it back in.

The issue with the starter clutch is this: when the clutch bell is spinning, the starter clutch is engaging the inside of the clutch, which makes the crank rotate. Thus, even if the clutch arms aren't holding onto the clutch bell, the starter clutch, which remember is attached to the clutch bell, is keeping the bell spinning and driving the rear wheel. This is what causes the bike to feel like it is holding on to revs for too long until you reach a very low speed. That's when the starter clutch finally disengages from the clutch. This also causes issues with throttling on from a lower speed, because what you want to happen is for your bike to spin up to what your clutch engages at again, so you get back into your pipe's powerband.

When you remove the starter clutch, your clutch disengages from your clutch bell at a much much higher RPM, which allows you to slow down and throttle back on much more comfortably and with a higher level of performance. The issue with this is that you need to drill start it (requires a fairly powerful drill), buy the kick-starter (which is hideous and I believe eliminates pedals), or work up a pull start.

I'm also quite certain the starter clutch causes launching issues with a high-performance setup. It feels like it grabs twice and not launch hard enough. I'm still working out what is causing this. I'm guessing that the clutch arms begin just BRUSHING the clutch bell, not yet fully engaged, but enough to spin up the bell and cause the starter clutch to grab, which then begins moving the bike sooner than you would like. Then the clutch grabs the bell and the launch is much less powerful.

So I hope this helps you understand why the starter clutch is one of the weakest links in a high-performing Hobbit, and should be removed by anyone who can work out a suitable way to start the bike without one.

Honda Variator (US Version)

The variator can be modified several ways. Notches can be added to allow a greater drive ratio change, and variator weights can be changed to change the RPM range (when the variator starts shifting) to better match your engine/pipe combination.

Variator Notches

Adding notches to the variator has been done several times by Moped Army members.

Here's the text that Justin provided when he did this mod: We cut notches for the rollers to stick out of using a hacksaw for the side cuts and a dremel for the bottom… we just scored the metal and used heavy pliers to snap off the little piece… then smoothed it out with the dremel.

The following picture is intended to show you how deep to cut your notches. You want your notches to "meet" the ramp, where it "hits" the outer edge. See the red line in the following picture:

How Deep.jpg

More pictures:

Variator Collage.jpg

Here's a picture of a variator caught with a fast shutter speed. You can see how far the rollers move. Not as far as you may think . . . . Also - it helps demonstrate how deep the notches need to be.

Full Open.jpg

Variator Weights (Honda)

The roller weight set has different Honda numbers. Variator weights are shown below:

Model Weight
Stock PA50II 14 grams
PA50II with 1/4" hole 11.7 grams
PA50II with 9/32" hole 10.6 grams
PA50II with 5/16" hole 9.5 grams
Stock PA50I 8.4 grams

The external dimensions are mostly the same, but the PA50I weights have much larger holes. The only other noted dimensional difference is the area that the plastic cap sits on. On some weights it is smaller, and on others, it is larger. See picture below.

Variator Weights.jpg

The weights. left-to-right are: stock PA50II; stock PA50II (weight difference is 0.2 grams compared to other stock PA50II); PA50II (with 1/4" hole); PA50II (with 5/16" hole); and stock PA50I.

Other dimensions are the same:

Weight size pic 1.jpg

Weight size pic 2.jpg

I've looked around for aftermarket variator weights, and I have not yet found any. When you look on-line, variator weights are identified by O.D., then width. That being said, Hobbit rollers are 15x16mm. The closest that I've found is 15x12mm. But - the channels of the movable drive face (the outside moving pulley half) are about 18.5mm wide. Ideally, it would seem that 15x18mm weights would be ideal, but this size, and anything even close doesn't seem to exist.

Now, I have drilled out a number of PA50II weights to make them lighter. Those with aftermarket exhausts and/or cylinders that have a power peak higher than stock can really benefit from lighter variator weights. See weight table above.

Variator Weights (Home Made)

A MopedArmy member has reported that he makes his own variator weights using 1/2" copper pipe, filling the pieces with lead, then drilling the lead out until the desired weight is acheived.

Homemade variator weights.jpg

This section will be updated later to provide more details on this option. I will say that this option is both good and bad, in my opinion.

The BAD: The stock variator weights use plastic caps on the weights - and these plastic pieces ride against the ramps of the movable drive face. Switching to a copper weight means that the ramps of the movable drive face will see more wear (at least compared to plastic). Since the movable drive face is more expensive to replace than a ramp plate, it is something to consider.

The GOOD: The outside diameter of the stock variator weights ride against the ramp plate, and this causes wear on the ramp plate. The copper weight should not cause the wear, or at least much less wear, meaning that the ramp plate will last longer.

Variator Weights (Aftermarket)

Currently there are two aftermarket variator weights available. They are made by Moped Factory aka MA member Graham Mohtzing. They are of the same weight and made mostly of plastic that wont smash up into little pieces. They are two sizes: 1 original stock size, and the other is slightly oversized in the event that you fucked up your variator notching.

Here is his tutorial:

Driven Pulley (US Version)

The driven pulley (the rear pulley) is made up of six parts:

All parts.jpg

The parts, left-to-right, top-to-bottom are: nut; spring; cam follower and seal (the seal is still installed on the cam follower), so it is two pieces; the movable driven face; and the driven face (I'm going to call this last piece the non-movable driven face). Let's talk about the piece parts.

Piece Parts

Non-movable Driven Face

Outer pulley.jpg

The "nut" on this piece is used when removing the driven pulley from the bike's transmission, and for disassembly. I used an air impact wrench to remove the small nut, but if you are using hand tools, you grab it here (while you are loosening the small nut).

Outer pulley 01 with taper highlighted.jpg

Note that the non-movable driven face "shaft" has a taper on it. This taper interfaces with the taper on the cam follower (see below). It is this taper fit that makes taking apart the driven pulley so difficult (unless you have the special Honda tool).

Movable Driven Face

Inner pulley.jpg

Here's the movable driven face.

Driven Face Cam.jpg

Inside, you can see that a cam has been riveted in place, using six rivets. The "ears" of the cam interface with the "ears" of the cam follower. Wear on the cam can cause operational problems, especially with bikes with variator upgrades (see Performance section below).

Innter pulley 02.jpg

Here's the other side - and the six rivets.

Cam Follower

Cam follower 02.jpg

Here a view of the cam follower. If you buy the special tool, it screws into the threads shown here. The cam follower itself has no other threads, just threads used for disassembly.

Cam follower 01.jpg

Here's what you can't see, unless you've taken the pulley apart. The three "ears" of the cam follower interface with the three ears of the cam (in the movable driven face).

Cam follower 03.jpg

In this picture, you can see the tapered area that interfaces with the taper on the non-movable driven face hollow shaft.


Nothing special here - just a spring. The Shop Manual says that a new spring is 72.3mm long, and a spring is too short when it gets to be 65.1mm long.


Driven pulley nut.jpg

Nothing special here. This picture does show how Honda staked the nut to prevent it from loosening. I would assume that Loc-Tite would do the same.


There is only one moving piece on the driven pulley assembly, it is the movable driven face. The movable driven face has a spring acting on it, causing it to move to a position closest to the non-movable driven face. At this "at rest" position, the belt is squeezed, and it will ride very high. As the front variator closes, the movable driven face moves away from the non-movable driven face, allowing the belt to ride lower in the pulley. The spring in the assembly is always wanting to move the movable driven pulley face closer to the non-movable driven face. As the front variator slows down (less RPMs), there is less force on the variator ramp plate, and the driven pulley spring will shift the driven faces closer together, and also causing the variator faces to separate.

Now, that how is looks from the outside. But what's going on inside. Actually, not a whole lot. The movable driven face, on the inside, has three "notches" in it, that interface with the cam follower.

Belt position with pulley fully closed.jpg

With the two pulleys at full travel (together), it looks like this.

Belt position with pulley full open.jpg

And this is what is looks like with the pulley fully open. Note that your pulley may not move to full travel. This can happen due to internal wear (see Performance secton below).

Sticking Problems?

I've had sticking problems in the past, when the pulley wouldn't open very far. I've had an amount of success spraying a penetrating lubricant into the pulley.

Spray here.jpg

You wouldn't have much to lose by trying to spray stuff in this groove. This groove is the only location where it will do you some good. When the pulley is fully "loose", you should be able to move the movable driven face with both thumbs - you'll have to press hard - but it should move. How far? See below.


Once you've got it apart, it is pretty easy to see how the parts go together. The spring is what makes it difficult to put together. You've got to compress it, and at the same time, start the nut. I'd recommend two people, one to compress, and one to put on the nut. Otherwise, you can just be inventive.

An item of attention is the amount of grease (the manual says 5 to 7 grams), and where it goes (and where it does not). The Shop Manual isn't really clear, but it is clear that you don't want any grease on the pulley faces, or the taper areas. I would put the grease on the inside walls of the movable drive face, and no where else.

Another item of attention is the two tapered areas - they must be squeaky clean. No rust, no dirt. I use Brakleen (a spray cleaner for automotive brakes).

Disassembly (Method One)

Removal from the bike requires a special tool. In addition, disassembly requires special tools as well - maybe. I was able to get it apart without special tools. I used an air impact wrench to take off the nut (on the back side of the pulley). That's the easy part.

NEW INFO 2019: A clutch puller for a Honda TRX 500 Rubicon works to separate the Hobbit rear variator cam follower and non-movable drive face -- No smashing or other abusive methods required.

Hobbit puller.jpg

The harder part is getting the cam follower separated from the non-movable driven face shaft. I tried about ten times first using a vice or a plumber's wrench (on the non-movable driven face nut), and vice grips on the back side of the cam follower. I had initially thought that the cam follower "unscrewed" from the non-movable driven face, so that's what I tried. It eventually did "pop off", but I should have been trying to rotate the cam follower in both directions (clockwise and counter-clockwise) to break loose the taper.

I also tried to strike the end of the non-movable driven face with a small hammer, and it didn't do any good. I don't think this would work very well just because you'd be applying force against the spring (the parts aren't "solid").

In the end, if you can get a Honda tool, I'd recommend it. Otherwise, brute force and luck will get you there, too.


Disassembly (Pavel's Method)

After struggling for a while with the pulley, I came up with a new method of removing and disassembling it without requiring special tools:

PA50 RearPulley Step01.jpg

PA50 RearPulley Step02.jpg

PA50 RearPulley Step03.jpg

PA50 RearPulley Step04.jpg

PA50 RearPulley Step05.jpg

PA50 RearPulley Step06.jpg

PA50 RearPulley Step07.jpg

PA50 RearPulley Step08.jpg

PA50 RearPulley Step09.jpg

PA50 RearPulley Step10.jpg

PA50 RearPulley Step11.jpg

PA50 RearPulley Step12.jpg

PA50 RearPulley Step13.jpg

PA50 RearPulley Step14.jpg

PA50 RearPulley Step15.jpg

PA50 RearPulley Step16.jpg

PA50 RearPulley Step17.jpg

Cutting half circles in each side of the wood jig can get the wood all the way to the hub, supporting the pulley more better.


New Spring

For other variated bikes, replacing the spring is often tied to a new performance varaitor. I've never seen any kit for a Hobbit / Camino that includes a new spring - but that's not to say it doesn't exist. The kit for the Derbi Variant includes a spring - but I haven't yet heard (or read) that it does a good job on the Hobbit.

Rivet Removal

I've read that some grind off the rivet heads on the movable driven face, to allow the face to move deeper into the non-movable driven face. Actually, based on my disassembly, and the width of a stock belt, this modification does not seem necessary. The belt drops fully into the "v" of the pulley when it is fully open.

In addition, if you grind the rivets off, I suppose it is possible for the cam inside the movable driven face to come loose.

Potential Problems

Notch in variator due to wear 02 with highlight.jpg

Here's the problem. This picture shows that, over time, the cam follower causes notches in the cam of the movable driven face. Normally, this is not a big deal.

But, let's say that you've got a PA50I (and you've just upgraded to a PA50II ramp plate) or that you've got a PA50II (and you've just upgraded by notching your variator). It is very possible, if not likely, that you've got notches on the movable driven face cam "ears". The problem is, that these notches can cause the movable driven face to only move so far, to the depth of the notch, and then "catch". My point is, if you're having problems with your variator not moving to its full position, then the driven pulley may be the cause (this should only cause problems if you've upgraded your variator somehow (like going from a PA50I to a aPA50II variator, or added a TJT variator) - or you know that the original variator was stuck for a long time, and it's just been fixed).

Limited travel due to notch 01.jpg

This picture shows how far this pulley would travel - then it hit the notch.

Limited travel due to notch 02.jpg

Here's what the limit looks like from the top.

Full travel 01.jpg

Here's what full travel looks like.

Full travel 02.jpg

Here's what it looks like from the top.

Honda Camino Driven Pulley (Europe Version)

All camino parts.jpg

Left to Right: Outer Pulley Half (the pulley half away from the bike); Inner Pulley Half (the pulley half closest to the bike), Pulley Pins (the pins "ride" in the outer pulley, and engage with the slots on the inner pulley), cup, spring, retainer cap, and clip.

Inner Pulley01.jpg

The internal pulley has two seals. Here's the inner seal (the seal closest to the bike). See the slots that engage the pins.

Inner Pulley02.jpg

Just a view through the inner pulley half looking at the slots.

Inner Pulley03.jpg

The outer seal of the Inner Pulley Half.

Outer Pulley01.jpg

A shot of the Outer Pulley Half.

Pulleys with pins.jpg

Here's a shot of where the pins would go during assembly. You have to "reach in" and place the pins, then the cup slides on, then the spring, the retainer cap, then the clip.

Easy to disassemble and re-assemble. No special tools required.


Here is a great place to get replacement belts. Very cheap, and order a few to save on shipping. If you have a performance variator, you want to adjust the rear wheel so that this belt rides as high as it can while still being able to start the bike. (not ride 2mm below the rear pulley as you would want for a completely stock set up.)

Click on the parts link below.

Honda PA50 Information
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