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As written by Pat (Long lost scooter freak to the masses lol

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The Ultimate 172cc Tuning Guide

Well it HAD to be done didn’t it....

Well its 3am on a Thursday evening, and I’m bored!
Summer is coming and now is the time all the new owners want to tune their scoots and get that extra few mph out of it, and sort out those 0-60 times ...

where to start, you have just bought a nice Standard Runner 125 sp (2 stroke) and you love it, but it needs that something else, that extra grunt! Here ill list simply where to start, what to do and what should be the last things to do, to your pride and joy!

To start with a runner 125SP is around 12BHP rear wheel and the first mod, is the single only mod to give such a massive gain...

1)Fit a Malossi 172 kit - £190
This kit consists of the Malossi 172 barrel, Malossi 172 piston and the Malossi head, and turns your machine from 124cc to 172cc. The 172 barrel is more reliable then the 125 and is around FIVE bhp more powerful due to the increased volume. a standard Runner 180cc sp is only 16BHP meaning the Malossi 172 kit has a clear 1bhp gain over the 180. Even though the 180 has 8cc MORE the porting in the Malossi kit is far superior since its a "race engine"

2) Fit a Gear up kit - £60
The standard gear box in the Runner/Dragster/SR/Typhoon 125s is designed to reach around 70mph and its designed for a smaller cylinder cc (125) when you fit a 172 kit in order to get maximum gain from it you want to make the gearing taller thus enabling you to reach slightly higher speeds, without running out of gearing. Its a sad fact no matter how highly tuned your engine is, if you have a standard 125 gear box you wont see over a true 75mph since there just wont be any more gearing left, you'll be revving its tits off but not gaining any extra speed. The Malossi Gear up kit is about £60 but needs to be fitted by a shop with a 10tonne press...

By now you will have a scoot that will have an amazing 0-60 time and will be doing around a true 80mph effortlessly!

3) Larger Carb setup - approx £200

This is where things start to get tricky, although the above Two stages are fine on their own if you want more speed you will have to upgrade the fueling to the engine. Now that you have a 172cc engine you need to throw the standard carb away (Dellorto phvg 20.5mm) and fit a big bad boy Dellorto PHBL 25(or 26)mm Carb,
The carb mainly boosts the mid end but can be setup to benefit all areas via clever jetting. Along with the bigger carb you will need to upgrade a few other linked areas.
You will now be able to fit an open air filter and get rid of that ugly air box. the open filter just allows the engine to suck in more air, it is pointless fitting one to a standard carb, let alone a standard 125 just for the looks - because it will be sucking in too much Air which in turn will mess up the air/fuel mixture and cause it to go BANG!

Two other upgrades in the carb dept I HIGHLY recommend is a Polini Inlet Manifold - This manifold is made of a stronger material then the standard one, and is pointed at a different direction, this means that when you fit a bigger carb, the Manifold wont flop and wobble about, and hit the carb on the rear hugger/engine casing! its around £40 and wont give you a performance gain, but as I found out you don’t go very fast with petrol pissing out of a hole in your carb!!!

Finally in the carb dept I highly recommend fitting a Malossi Reed Block (£45) this reed block has a larger surface area and inlet then the std one and allows more fuel to be pumped into the casings! The malossi reed block is the biggest you can fit in the casings without major modifying!

4) Upgrade The Transmission

Now That you have all this extra power and grunt you need to get the best setup to get the power from the engine, to the wheel as fast and smooth as possible. You do this by a mixture of certain weight rollers, different strength clutch springs. the possible upgrades to the variator are large, both Polini and Malossi make a Variator kit however many top tuners (and myself) recommend using a standard 180cc Variator from a runner/dragster. These are just as good as the malossi’s and don’t cost £90!

To cop with that extra power you will need a stronger belt, Usually it is best to go for the Malossi Kevlar belt (£30) an average malossi belt will last around 4,000 km before wearing, but it all depends on the state of tune of the engine, and the riding conditions whether its in the city, or countryside etc.... HOWEVER if you have a 180cc variator it is recommended to use a Polini Kevlar belt. The Polini belt is at a slightly different angle which matches the 180 variator perfectly, whereas the Malossi belt is designed for the Malossi variator + 125 variator!

At the back end of the transmission you have the clutch and just like the variator there are many different choices.

Malossi's top seller is their "Delta Clutch" which has a unique setting feature where you twist the spring themselves rather then fitting different tensioned springs, however this doesn’t come cheap £90 is the price tag it carries and then needs some1 with a half technical mind to keep adjusting the clutch to get it perfect.

Polini have kept things simple with a straight forward sports replacement, it looks like the standard one except the clutch arms have slight groves cut out of it and the springs are shorter. I HIGHLY rate this as I used this in my street setup for ages and with a price tag of only £45 you cant really go wrong

Finally save the best for last - Standard clutch, This is what i run now on both my sprint and road setup since the clutch itself is fine, i just run a Stronger Malossi contra spring and stronger Malossi outer springs!

Malossi make 3 types of springs,
- Soft (basically same as standard) [blue]
- medium (revs to about 5,500RPM before it engages) [green]
- hard (totally lethal for road use!) [red]

5) Sports exhaust

Most people want to fit the exhaust first because it "looks cool" " sounds cool" or whatever - the fact is that the exhaust gives the smallest power gain and with a price tag of up to £270 and a possible life of 400 miles for the pipe! Its a waste of money

The standard pipe is very good but once you get to the above setup there’s only 1 last thing you can do, and that’s upgrade the exhaust. There are many different types and I’m going to give a rough pro/con of each of the pipes.

Scorpion Stainless steel exhaust £200
- This Pipe is one of the most popular ones, it comes as standard in stainless steel meaning it wont rust or corrode, and also it is very strong and only the early models seem to have reliability problems with snapping etc. The Cons are that it doesn’t really give that great a power gain compared to some of the all out race exhausts. The scorpion comes 'E' marked meaning its road legal however i have heard that the police are now not paying attention with E marks and declaring all replacements as illegal!

PM Tuning '55' Exhaust £200
- This pipe looks identical to the scorpion shape wise but isn’t stainless steel, it comes as standard in its 'bare metal and weld' style which leaves it prone to very fast corrosion. Another common problem seems to be the muffler straps snapping, however the main body of the pipe seems to be pretty much trouble free, but still not as reliable as the scorpion. This exhaust Pro's are that its the same price as the scorp but gives slightly more power, and is able to release more power the more tuned your bike is.

PM Tunings '59' Exhaust £270
- This is the brother of the successful 55 Exhaust, with a totally new funked up design with a 360degree curl in the neck lifting it up high! this exhaust can add up to 2.5bhp power gain just by bolting it on, and like the 55 it comes as standard in untreated bare metal, looks good but wont last through the winter if left untreated! However PM Tuning seem to of slipped up here, as most of the PM59s snap within 1000 miles (on occasions at 400miles of being new) and by 12 months the average PM59 will have more welds then the titanic and we all know what happened to THAT!

Malossi MHR race exhaust £350 [i]
- The Malossi pipe s the most expensive pipe out there as far as i know, and unlike the above 3 exhaust its an all out 'Race pipe' - it is VERY high revving and designed for maximum tuned and ported engines with as I said very revvy setups! The pipe itself is very sexy its a rather upswept curl back exhaust that unlike the 55 and scorpion doesn’t protrude past the rear wheel, it lifts itself up exposing the wheel (not a good thing if you have a battered dirty rim!) the pipe itself is rated as the best all out race exhaust and cant be faulted apart from it being slightly brittle.

Polini Evolution MK3 [i] £250 - Right in the middle of the price range, the Polini Evo mk3! I’m Bias as I have fallen in love with this pipe but it has so many great things about it. It too has the upswept look and is short meaning it looks small like a 50cc exhaust and exposes the rear wheel uniquely! It is angled so you can actually take the rim off without removing the exhaust. and the best thing has to be the mounting of it. It has 2 giant rubber pods between the pipes bracket and the engine mount! Meaning the pipe is allowed to move to a degree which means it’s as strong as a tank! I thrashed mine for a few good months and never had a problem unlike the many other exhausts I had tried! the only down side being that its a all out race pipe it does need some fine tuning like the malossi but if you can be bothered for a few days to set it up perfect the rewards are endless!

For the Aprilia SR (written by TangoSR)

PM Tunings ‘52’ Exhaust £240- PM Tuning Racing Products own handmade expansion chamber suitable for Aprilia SR and Piaggio Typhoon 125cc - 172cc standard and tuned cylinders. This exhaust gives approximately 2bhp over the standard exhaust... PM X-tech lightweight construction less than a 1/3 of the original. Power increase + 2HP +8 MPH. Main jet included no roller weight changes required bolt on and go. These can spilt as the are intended for “race use only” so aren’t made to last like the legal pipes you can get, but saying that I haven’t had any problems with one of these fitted to my Aprilia SR in the two years I have had it (bought secondhand as well)

There ARE cheaper exhausts such as technigas and kundo, however there not really worth mentioning!

once you have all of the above and your wallet is about £600 lighter from parts and labour all you need to do is get it setup perfectly, PSN tuning are doing a £60 (+vat) collection + delivery home dyno testing, meaning they will come and collect the engine from you, bring it to Yorkshire, put it into their test bike and dyno test your engine and get it setup perfectly! - And should only take maximum of 2 hours labour!

With all the above bolt on’s your looking at 22-23BHP an improvement of 11bhp almost double standard power! The bike will do 90-95mph true speed all day long and the take off will be totally mad, that you cant even imagine!

6) Crank Shaft

I didn’t know where to list this as its the most expensive replacement part and will cost in the region of £400 including labour to get the Malossi Crank fitted!
The truth is that with the standard crank you have a 50/50 chance of it snapping and taking all your tuning goodies with it! The crank itself costs £230 and you will need new seals and bearings (£40) so its £270 in parts and to fit the crank is a good few hour’s work which really needs to be done by a specialist! My crank snapped when I only had a 172 kit and 25mm carb which wasn’t even working to its full potential! And that was after only 5,000 miles! Many others standard cranks have gone, and the other 50% are just a ticking time bomb! If you are serious about your bike and are planning on tuning it more, and keeping it for a good while [and using it every day] you Must get the crank as the Malossi crank will take as much abuse you can throw at it without snapping or damaging (unless your names Joe B )

That’s it, that’s everything you can bolt on, everything to get you double the standard power and up to 95mph!

Setting up

- We all know that’s there’s not just 1 setup for everybody, its all trial and error really however I recommend the following to keep in your head!

Rollers
standard variator with just stages (1-3) - 13.5/14g Rollers
Malossi variator with stages (1-3) - 13g/13.5g Rollers
Standard Variator with mild tuning (1-6) - 12.5g Rollers
Malossi Variator with mild tuning (1-6) - 12g Rollers

If you have a sports exhaust I recommend trying out some Green (medium) clutch springs with 12g rollers,

Jetting

With my fully ported 27BHP engine and the polini pipe I was only running a 110 main jet with a 42 pilot But that was a very very lean mixture! So only use that as a guide line so if you’re running a very high spec with stages 1-6 I recommend starting at around 112-110 and working down till you find your perfect jet size.

Remember Tuning is 50% parts and 50% set up, if you don’t have access to a dyno (you have no reason to be without a dyno with PSN's new deal) but if you cant afford the engine to be sent off, road setting up your own engine isn’t just a long and tiring process it can be fun and allow you to find out and know so much more about your own engine! And develop your own setup to suit your riding style/weight/location etc! Meaning you have a totally custom setup!
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