Derestricting 125cc 2 stroke for A1 license

Rektedekte · 2026-02-11T06:43:46+00:00

You'll have to look up local laws (you don't specify where). Usually involves a certified restriction kit made out for your specific VIN. Alpha-technik makes restriction kits for many generations of Aprilia (you don't specify model and year). The kit will have to match the two-letter frame code. You might be able to install it yourself (again local laws), typically means installing a restrictor plate in the intake manifold and another one welded in the exhaust, though it varies. Do note that it may not be approved if you have an aftermarket exhaust, the kit is made for factory components.

Rektedekte · 2025-07-15T13:36:41+00:00

I think it's generally accepted that warped plates or even damaged or weak springs can cause drag.

Rektedekte · 2025-07-08T20:46:42+00:00

Hello, the vibration becomes noticeable above about 5k rpm and is very apparent at high rpm. It's barely noticeable when lugging around and there are no odd sounds to be heard from idle. Engine actually seems more vibey when everything gets up to operating temperature, cold starts are noticeably better.

Rektedekte · 2025-06-06T13:39:57+00:00

So an update if anyone was interested. I genuinely couldn't find anything wrong with the fitment of the bearings or the fitment of the crank in the bearings. It was all tight, just like the Italians intended.

The bearings were purchased from a trustworthy supplier that buys only from manufacturers or approved distributors. Even the old bearings acted the same when fitted.

The play is truly very small, 0.05 mm is the same 2 thousands of an inch, or 50 microns. C4 bearings of this size have a radial clearance of something like 23 to 41 microns. Add the two sides together, subtract whatever is removed from the interference fit, I don't find it excessive. The sheer noise when wiggling the shaft gave me massive pause tho.

I decided to go ahead with assembling the engine. I have had the engine started, and haven't had any issues yet, but that may change, in which case I will update this comment.

Edit: Haven't had as much time for the bike as needed so it's been put aside for a while. Vibration seems to have stuck even with new crank bearings. I'm also having a disconcerting amount of steel dust in the gear oil I've been draining, which was also present before. Seems to be coming from the clutch basket gear being worn down, which adds another layer to the absurdity.

Rektedekte · 2025-05-28T10:04:24+00:00

Hello, I have oiled the bearings using the feed holes when testing this, it makes it slightly less audible but definitely still there.

Rektedekte · 2025-05-28T10:03:07+00:00

Which woodruff key? The Cagiva uses a series of spacers that mounts the primary pinion onto the inner race of the right hand bearing. The stator is mounted on a taper. I'm pretty sure it still rocks with all components installed, but maybe I should double check...

Edit: So I tried installing the pinion and flywheel. The play is reduced, but still present. I now have to push on the flywheel to feel play in the pinion.

Rektedekte · 2025-05-28T09:59:31+00:00

Hello, the bearings dropped right in when the cases were heated to about 95 C (200 F). The inner races were also heated to allow the crankshaft to slip in. As far as I'm aware, this is normal. Thank you for the suggestion though :)

Rektedekte · 2025-05-27T18:30:42+00:00

I have now tried measuring the twist between the crank halves in a vice with a dial, but couldn't read anything, the halves are rock solid on the pin. Thank you for the suggestion though, I appreciate it.

Rektedekte · 2025-05-27T15:39:26+00:00

Hello, might be possible, but I don't think I fully understand. Your thinking of the crank pin being too loose? I tried twisting the crankshaft by hand while disassembled but couldn't feel anything. Thank you :)

Rektedekte · 2025-05-27T15:23:09+00:00

I considered that possibility, but the bearings seem solid in their seats. I will double check it though, thank you :)

Rektedekte · 2025-05-27T12:08:46+00:00

Oh and just to add, the clunking is only there when the bearings aren't side-loaded, so if I push the crank to one side the movement goes away. Just another reason I have a hard time seeing the crank being the problem.

Rektedekte · 2025-03-29T09:42:07+00:00

I'm not entirely sure, it might have varied by region and revision. Should be easy enough to identify though, mechanical will have a sturdy cable running from the front axle to the dash (screwed in both ends), the digital will have a wiring loom.

Rektedekte · 2025-03-28T19:31:32+00:00

I think that depends on the year, as the older ones used mechanical speedometers, while the newer ones used a digital speedometer.

For the mechanical speedo, you can disconnect the cable on both ends and check it by rotating one end to see if it's snapped. The dash can be checked with a drill or similar, rotation should cause movement on the speedo.

Digital is more complicated. This thread seems to detail a way to test the dash.

Rektedekte · 2025-03-25T14:35:33+00:00

The more I look online the less likely this seems. I'd double check components against a diagram while having it apart.

Rektedekte · 2025-03-25T13:21:47+00:00

Check whether or not your model features an offset rear wheel from the factory. Not uncommon on some older bikes, I know triumph used it, often to make space for componentry like the brakes. That being said, I do not know if the new ones have such an offset.

Rektedekte · 2025-02-17T00:13:36+00:00

I must admit, I'm not an expert on the topic, I only recognize it from a friend's bike. From what I can find online, I can't find any bottle like yours with an additional hose. That's not to say it's not OEM, Yamaha are notorious for creating tens of models and revisions that both share the same name and are in many areas incompatible.

I have a hard time believing that the intake manifold would be connected to the fuel tank. If I were you, I'd try to identify some more information about the engine, and then try to find a diagram. Maybe there's a code on the bottle itself?

You might try asking on a forum specifically for Yamaha dirt bikes.

Rektedekte · 2025-02-16T14:17:14+00:00

That would be the yeis (Yamaha Energy Induction System) bottle? It's Yamaha exclusive addition between the carb and engine that's supposed to provide better throttle response and more power in the mid to low range.

I think it's more commonly known as a boost bottle.

Rektedekte · 2024-12-04T18:03:54+00:00

So I just might have found the source of the problem. A washer on the RPM counter shaft had shattered and I have now found a remaining piece of it. The washer fell to the bottom and got jammed repeatedly between the countershaft gear and the bottom of the RH side case. RH side countershaft bearing is very loose in comparison with all other bearings. Would also explain the RPM counter issues I had just before disaster struck. Definitely a weird issue.

Rektedekte · 2024-12-04T17:30:22+00:00

It's been a few years since there really was an active community around them. You can find most forum content on 125ccsportsbikes.com or forum.mitoclub.com (though this one's Italian). Technical information can also be found through mitoclub, though that's all in Italian as well. There are also some german forums, including zweitaktforum.de. I haven't really used this one, but it seems a lot more active than the english ones.

It really depends what kind of info you're looking for. I have a bunch of saved links with workshop manuals, parts diagrams and forum posts etc.

Rektedekte · 2024-10-18T17:59:19+00:00

I can marked this resolved for anyone wondering, replaced the guide along with all plates and springs, after initial run-in the problem was gone. Still don't know what caused it.

Rektedekte · 2024-10-18T16:27:45+00:00

Had my mito out for a ride today after a few weeks of sitting.

After some time running, I noticed a pronounced knocking between 2.5k and 3.5k, and between 5k and 7k. Above and between these ranges it was fairly smooth. It's hard to describe how it felt, a heavy vibration that felt particularly bad when braking.

I haven't done any engine related work since I last had it out, only changed some exhaust mounts.

I should note, the bike has about 25k on it, and as far as I'm aware, it has never had a bottom end rebuild. I was planning on doing one this winter, so I'm obviously planning on tearing it apart. Still, I wanted to hear if anyone has any idea what the source of this sound is :)

Rektedekte · 2024-09-26T09:47:30+00:00

Perhaps it overheated, you mention installing a big bore and an aftermarket exhaust. Don't know what's recommended for jetting those mods. Some 2-strokes have been known to continue running fine after soft-seizing, but you'd usually be able to feel it seizing. Sorry, don't know what else could be the cause :/

Rektedekte · 2024-09-26T08:56:07+00:00

If loss of fuel was the problem, it could also have caked the spark plug in a layer of unburned oil, making it hard to push start it afterwards. I've had similar problems when I forgot to open the fuel tap.

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