This blog is a follow-on from our short blog introducing the basics of dynos "Dyno Moped Tuning" and is intended to show how a dyno can be using in the workshop to very quickly setup a modified moped.
The follow is only a very basic setup which can be done very cheaply (approx £40) but still normally makes a very significant difference and takes about 30 minutes. Our workshop does dozens of setups like this every month.
Case Example
The moped used is an '08 Yamaha Aerox 50cc '08. The customer bought the following parts...
Leo Vince ZX powerpipe
Stage 6 Sport Pro 70cc Kit
Polini Open Air Filter
Malossi Gearup Kit
and fitted them himself...
He also rejetted up from size 62 main jet to size 82 (~32% increase) and dropped the roller weight from 5.5gr (standard) to 4g
He'd been driving it around for a few days to run it in and wanted us to check it was all set up properly and not going to blow up (!)
The first thing we do is run the bike up on the dyno to see how it performs. This gives us the graph below...
(Click on the graph to enlarge it)
Ok, so what does this tell us ?
First of all from the top graph we can see the engine is making almost 10hp at the rear wheel, which is a perfectly good peak reading for the setup. What the top graph also tells us though is that it isn't actually making this peak power for very much of the time. You can see it's making more than 9hp only between 18 and 26mph, at 30mph it's dropped down to around 5hp and creeps back up to over 8hp between 39 and 42mph after which the power drops off very quickly.
If we look at the 3rd part of the above graph which shows the engine revs we can get a good idea of why. In a previous blog Malossi Sport vs Polini Sport vs Stage6 Sport Pro 70cc we ran up a few different cylinders on an aerox with the same Leo Vince ZX pipe which gave us the following graph...
(Click on the graph to enlarge it)
This graph is a special test run with the variator locked which shows us that the Stage 6 Sport Pro with the ZX pipe makes maximum power between 8900 and 10500rpm. In fact this is a very wide peak powerband if you compare it to the Malossi or Polini Sport kits, so it should be easy to setup. All we have to do on our customer's moped is make sure the revs stay between this range and we should have 10hp available all the time. If we look again at the top graph we can see that where the bike is not performing correctly corresponds exactly to where the bike falls out of this rev range. For example up unto approx 25mph the revs are above 9000rpm and consequently we have high power output... at 30mph we can see the revs have dropped right down to 8000rpm which is simply too low, the Stage6 70cc kit is only making 5hp here.
It's the job of the variator to hold the revs as dead steady as possible. Unfortunately the Aerox standard variators are notoriously poor at doing this. On a standard cylinder with a wide powerband it doesn't matter so much if the revs wander about, but on a modified bike with a narrower powerband this becomes a real problem because the moped can easily drop out of its powerband and it's normally necessary to ditch the standard variator and replace it with something decent to hold the revs steady to get good results. Incidently our variators of choice are Malossi Multivar or Stage6, both of which perform superbly well. We used to also rate Polini variators very highly until they were recently replaced by the new cheaper 'High Speed' model.
You can see in the top graph that our standard Aerox variator allows the revs to wander between max 9500 and min 8000 revs, which is a range of 1500rpms and a huge change- however because we've already established that the Stage 6 Sport Pro Kit makes peak power between 8900 and 10500rpms (a range of 1600rpms) we might just about be able to make it work with the standard variator.
It's worth noticing though that the Polini Sport and Malossi Sport kits make peak power only for a far smaller range of around 500rpms and there is no way they could be made to work properly with this standard variator, they would need a decent aftermarket variator which can hold the rev range within 500rpms across the whole speed range of the bike and the bike would have to be set up carefully to make sure it stayed within this range.
This is one of the reasons we like the Stage6 kits so much, they make more power than the other kits in their class and are far easier and more forgiving to setup.
Ok, now let's take a look at the fuel mixture (jetting) this is in the 2nd part of the top graph. From our previous blog "Dyno Moped Tuning" we know that we want the AFR to be running around 13:1, from the graph we can see that our moped is spending most of its time running at over 16:1, this is much too lean and the jet needs to be bigger even although the customer has already increased from 62 to 82. Although the bike will seem to run ok and makes good power there is a serious risk of the engine seizing on a long run with this sort of reading. Having more fuel present helps to keep the cylinder cool, if the bike is too lean the piston will expand until it is big enough that it starts to no longer fit within the sides of the cylinder. This additional rubbing friction very quickly overheats it more and in turn the piston becomes so big that it jams against the sides of the cylinders often causing the engine to lock. On a manual geared bike this would involve either a locked rear wheel at high speed (scarey) or a trip over the handlebars, luckily on a moped the transmission usually just disengages harmlessly. If you're paying attention you may notice the warning signs as the moped starts to loose power before it actually seizes (due to the additional friction between the enlarging piston and the cylinder walls) and back off or let it cool down. If you're lucky the bike might run again after leaving it to cool down once it's seized but probably with reduced power.
When you take the cylinder apart you can usually identify this type of seizure by the fact that the piston rings are often 'melted' into the piston rung grooves and consequently no longer spring out at all.
There is a lot of mis-information being spread about moped jet sizes. If you fit a sponge type air filter you will normally have to increase the jetting by around 50% to avoid risking engine damage or unreliability (Piaggio even bigger, a Piaggio 50cc will amazingly sometimes need over 100 jet to run well and safely- basically you want the biggest jet size the moped will perform well with, just keep increasing the jet size until the performance starts to drop off and then go back down one step.
Here are some jetting increases for Yamaha Aerox *only*.
- Standard Aerox, standard airbox, standard exhaust :- 62 jet
- Sports exhaust :- increase from 62 to 68 (summer) or 70 (winter)
- 70cc Sports big bore kit :- no real change in jetting, perhaps increase of 2
- Open air filter e.g. Polini Open Air Filter :- increase by another 28 this can depend on the filter fitted, if fitting a covered open air filter such as Malossi Covered then increase by
18 instead of 28...
We obviously can't take any responsibility for people using these jettings but they based on literally hundreds of runs and are normally a good starting point so long as there are no other problems with the bike such as air leaks etc.
So... as in the example of our customer's Yamaha Aerox with sports pipe, 70cc kit and Polini open sponge air filter we're going to rejet it with a 96 jet and see how it goes. We're also going to drop the roller size by 0.5gr which isn't much, but we're expecting to see a power improvement from the larger jet so 0.5gr might be all that is needed. We're also going to slightly change the weight of the rear torque spring back to a standard one as it seemed to have had a heavier one fitted which we think could be adversely affecting the variator function. You only really need a stiffer torque spring for very high power bikes, basically the spring just has to be strong enough to stop the belt from slipping, any heavier it will just grip the belt too tightly and lose power due to the additional drivetrain frictional losses.
Also the customer had fitted a standard Aerox short reach plug, but the Stage 6 kit is designed to run with a long reach plug. Using the short reach plug lowers compression and can easily result in a drop of 0.5 to 1hp at certain rpms.
So... despite all the talk all we've actually done is change the spark plug, changed the main jet, tweaked the roller weight and changed the torque spring, let's run the bike up again and see what we affect this has...the green line is our new run
(Click on the graph to enlarge it)
We can see straight away that we now have more than 9hp available all the way from 16mph right up to over 65mph whereas before it was only between 18 and 26mph. In fact before the bike wouldn't run much over 50mph (probably showed 60mph on notoriously inaccurate moped clocks), now makes a genuine 70mph and with almost 10hp immediately available at any speed the acceleration is obviously massively improved. With the drivetrain tweaks the variator is now able to entirely maintain the engine revs between 8900 and 10,000rpm which is exactly within the peak powerband of the Sport Pro kit as discussed earlier.
We can also see that the mixture is now firmly in the safe zone so no risk of seizures.
This dyno work is obviouslyat the very basic end of tuning, we could make more improvements by spending more time and money on the bike, but for just 30 mins work and a charge of £40 +rollers and a jet the customer is certainly going to notice a substantial difference for his money with the bonus that it's not like to seize as it was before.
Next time we'll progress onto some more advanced performance mods ! Happy tuning !
..with a dyno !
This is a basic introduction to dynos and moped tuning. This blog just covers the basics of what a dyno is and the difference and limitations between different dynos. It is only really basic, but the next blog will cover some actual basic moped tuning and moped setting up using a dyno.
A dyno is something that is normally out of reach for most scooter or moped tuning workshops within the UK. The cost simply isn't financially viable for the returns. The market for moped tuning doesn't exist commercially in the UK, the biggest moped racing class in the UK has hardly more than 10 entrants per year meaning that except for perhaps a small specialist shop the main commercial market for moped tuning would be 16yr old school kids with an Aerox or Piaggio Zip which they want to go faster than their mates' bikes!
Given the large investment and running costs of a dyno, dyno moped tuning is clearly not a golden goose commercially and reserved solely for the pure enthusiasts
We are in the lucky position that because we also setup superbikes which involves a lot of fuel injection work and requires the use of a high end eddy brake dyno, we have a dyno which normally wouldn't otherwise be accessible to mopeds. This is because the hourly rate these dynos command can quickly exceed the value of a moped, and normally the sorts of workshops or race teams owning them are superbike specialists with no interest or experience in mopeds
Whilst a few moped tuning shops can afford a basic dyno they tend to be budget intertia models. An intertia dyno works by measuring the time taken to accelerate a load (i.e. how long it takes for the moped wheel to accelerate the dyno drum) and then mathematically calculates a hp reading over the speed increase. So basically you start it recording and record a single run with wide open throttle (WOT) as it accelerates to top speed.
Basic inertia dynos are certainly useful but have a number of limitations for moped tuning. Firstly the actual hp readings vary widely between them and need to be taken with a pinch of salt, but for the tuner the accuracy of the readings actually aren't too important, you just need a comparison so as you can compare changes you make to the moped or bike to see the effect. So if you tweak your timing or change your carb all you really need to see is a comparison of before and after with the actual figures not being too important.
This introduces the first problem, engines develop different power depending on atmospheric conditions. For example in cold weather the same volume of air contains more oxygen than it does in hot weather, so if you dyno your moped on a warm day and then dyno it again the next day with a new exhaust when it's cold and wet how do you know if any changes are due to atmospheric changes or to the exhaust?
Because of this it's necessary to have some sort of climate monitor when moped tuning. Our dyno has an external weather station will measure humidity, pressure, temperature and relative air density and from this data will calculate 'corrected' compensated hp figures. With this system you can get virtually identical readings when moped tuning whether in the snow, in the summer or on top of a mountain (!)
Another absolute basic requirement of a dyno is to have an air/fuel ratio monitor (AFR). This is how you tell if the bike is running lean or rich. The AFR is the ratio of the mass of air compared to the mass of fuel. With petrol the ratio of air required to completely burn all the fuel is approx 14:1. With moped tuning we find that normally the moped will make maximum power at around 13:1. The AFR (mixture) is measured by a probe which goes into the exhaust. When moped tuning we normally are only really interested in the mixture when the bike is running at full throttle and under load (as if it was riding on the road with a rider) so in basic terms it's just a matter of changing the main jet until we get a consistent reading of 12.5 - 13. Also at this slightly lower ratio the mixture is richer which helps cool the cylinder and piston to prevent seizures.
The next problem with budget end dynos is that mass of the dyno drum is often very low. This means that it's easy for the drum to be spun up and the moped will accelerate faster than it would in real life. Because of this the moped engine doesn't experience the same load or strain as it would in real life which can adversely affect the relevance of any readings and tuning results which may not be duplicated in real life and allows the moped to run at unrealistic speeds. Imagine tuning your moped and testing it just by doing downhill runs- if you set everything up like ignition timing at this lighter load when you finally decide to go uphill and put some real load on it you may find things very different or even disastrous !
The drum mass of our dyno is approx 500kgs (almost the same as a small car !) This ensures realistic loads are placed on the tested bike even when running in inertia mode.
Besides this our dyno has a load cell eddy brake. This is an extremely useful (but very expensive!) piece of kit which can be fitted to high end dynos. The load cell allows the speed of the dyno drum to be computer controlled by extremely powerful electromagnetics. This adds a multitude of options to the dyno tuner. For example you can program it until it exactly replicates the performance, acceleration and top speed of the bike in the real world. In the real world the air resistance against the bike increases by 4 times each time the speed of the bike doubles. This can be accurately replicated by the load cell. Perhaps you're tuning for a hill climbing event, again you can realistically replicate the real world higher loadings to get realistic tuning results
Say for example when moped tuning you want to see the effect of changing the ignition timing on power or torque at different engine speeds. An inertia dyno can only measure power whilst the drum is accelerating so you would do a full run which sweeps through the rpm you're interested in and read the graph to get a reading and keep repeating with different settings. With the load cell you just set the drum to hold the engine at say 7000rpms. No matter how hard you throttle or how powerful the bike, the magnets will hold the drum at the speed which will keep the engine at 7000rpms. It will continuously read a 'live' hp reading at this steady rpm calculated by how big the load the magnets have to apply to hold the revs steady. You can then hold the throttle fully open and adjust the timing whilst observing the effect on power, or then repeat at different throttle positions or different rpms and see instant live comparison readings.
It's almost impossible to setup fuel injection or race bikes without a load cell or eddy brake dyno. With moped tuning, when setting up a carb at a basic (but perfectly acceptable for road use) level you only really need to pick the correct main jet so as the mixture is correct at full throttle under full load. Because the variator holds the revs fairly constant this is fairly easy. Eventually the moped will reach a speed where the variator has finished changing all the way out the moped revs will inevitably increase which can then affect the mixture. Normally we make sure that at this point the mixture becomes richer as the revs increase for engine safety reasons, but otherwise moped carbs are very forgiving and it's normally just a case of finding the best main jet for normal road use.
Motorbike carbs can be trickier, because of the higher power of motorbike engines they are often ridden at different throttle positions (a moped throttle normally spends its life fully open) and across a wider range of rpm- the jet that works perfectly at full throttle at 7000rpms also has to be made to supply the correct mixture as well as possible also at half throttle at 5000rpms for example.
With fuel injection you can have much more control (not including fuel injected mopeds!). With an injected superbike we can plug a laptop into the bike fuel injection system and adjust the mixture to make it leaner or richer at any rpm and at any throttle position. With our load cell dyno we can then program the eddy brake to allow the engine to increase in steps of 500rpms and hold it there for a few seconds before stepping up the next 500rpms. So we might start at 10% throttle and set the 'jetting' (mixture) correction with the laptop using the dyno air/fuel analyser at every rpms so as it is perfect and then repeat the whole process over and over at other throttle positions. In total there are around 250 different rpm and throttle positions combinations all of which you can precisely set the mixture at. The whole process can take up to a couple of hours but at the end of it you know that whatever throttle position and whatever revs the mixture is always absolutely perfect. The result is an exceptional smooth ride with maximum performance when accelerating from any throttle position at any revs.
There is actually a fairly new breed of low intertia dyno which does in fact use a very low weight drum. It does however bear little resemblance to the budget low drum weight dynos as it uses an eddy brake module to replicate the effects of a much heavier drum and all the other benefits of a load cell dyno and certainly doesn't fall into the budget category !
Next time we'll show some basic dyno moped tuning examples on customer mopeds complete, to demonstrate how quickly and easily the performance of a moped can often be transformed simply by setting it up correctly !
Wiring pinouts for Yamaha Aerox Speedo Clocks Assembly
This is the most common one we get asked for.
This shows the connector snipped off from the old speedo clocks, you can obviously connect your shiny new Koso Clocks or Stage 6 digital clocks directly to this or however you prefer.
Quick note on the most common problems people have when fitting the magnets - if you drill a hole into the brake disc or disc bolts to house the magnet(s) the magnet(s) *must* stick out *at least* 1mm proud of the hole they're recessed into. If they're flush they won't work correctly. The airgap between the magnets and the pickup should be 0.8-1.0mm. The more magnets you use the smoother and more accurately the reading will update when your moped is speeding up or braking.
Multiple magnets *must* be spread out evenly, so for example if you have a Gilera Runner with a 5-hole brake disc you can't fit 2 or 3 magnets if you're using the disc bolts to mount them because they wouldn't be spread evenly.
If you have a 6-hole brake disc for example then you could use 1,2 or 3 magnets.
Don't forget to set the clocks for how many magnets you're using and the wheel diameter!
How to test a moped automatic choke unit
When a scooter engine is cold it needs a richer mixture (extra petrol) to start and run. In the briefest of terms this is because petrol in liquid form does not actually burn, it's the vapour it gives off that burns. Petrol vaporises much more slowly when it's cold, hence you need more of it to create the same amount of vapour. The choke circuit provides a method of increasing the fuel supply until the moped has warmed up and then shuts off, either by a manual choke which you switch on and off yourself or an automatic choke which does this for you.
Either way the choke is just a simple plunger which opens or closes (blocks off) a small channel inside the carb (the choke circuit) which allows (or doesn't allow!) extra fuel into the engine.
If you look at this manual choke here...click here... you can clearly see the plunger which is simply lifted up or down manually by the black lever to open or close the moped choke circuit as the rider wishes. You can see the same plunger in the photo of the automatic choke at the top of the page.
You'll notice that the automatic choke has a needle on the end of the plunger whereas the manual one doesn't. The needle allows the automatic choke to gradually allow less and less fuel to flow through the choke circuit until it finally closes it fully after the engine has been running for a few minutes. In contrast the manual choke is simply on or off, nothing inbetween !
How does an automatic choke work?
Inside the automatic choke there is a small wax capsule with a heater coil wrapped around it. When the engine is started a voltage is applied to the heater and the wax heats up. As the wax begins to heat it expands and pushes the plunger out slowly. After approx 4 or 5 minutes the plunger is fully extended closing off the choke ciruit and no longer allowing additional fuel to flow. As soon as the engine is switched off the wax capsule begins to cool and the plunger is slowly retracted again after about 15 minutes.
The easiest and surest way to test the choke unit is to test it on the bike.
- Start and run the bike (fast tickover is fine) for at least 5 minutes. (This should ensure that the choke plunger is fully extended)
- Switch off the engine and *quickly* remove the moped choke unit. You need to do this ideally within 30-60 seconds max of switching off the engine, so make sure you've already removed any panels beforehand which are in the way. To remove it just under the 2 screws holding in the horseshoe 'U' clip and pull it out. Measure the distance A as shown as in the picture below
- Now leave the choke for at least 20 mins to cool down and measure the distance again- distance B in the photo below
You'll be able to get a good idea if your choke is working correctly by comparing to the pictures and whether or not the plunger has retracted, but for reference distance A should be at least 2mm greater than distance A
There are 2 possible reasons for the unit not to work. Either the choke unit itself is faulty, or there is a problem with the power supply to it. If you have a multimeter you can test the power supply by disconnecting the automatic choke and touching the meter leads onto the wires which the choke was connected to whilst running the engine at a fast tickover - (make sure not to touch them together!)
The wires should give you a reading of 12-14volts AC. Note that the choke normally runs off the lighting circuit which is usually AC on mopeds, so make sure you test with the meter set to AC as well as DC! The choke itself will work off either AC or DC so as long as you have 12-14 volts there in either DC or AC the power supply is fine.
If you don't have a multimeter you can test the choke by removing it from the bike and connecting it directly to a fully charged moped battery using suitable wires (be careful not to short the wires together!). It doesn't matter which way round the wires are connected to the battery.
After 5 minutes of being connected it should have fully extended as in the 'hot' photo above and subsequently retract as in the 'cold' photo after the battery has been disconnected for 20 minutes.
If the plunger still doesn't move the choke unit is faulty and will need replacing.
You can either replace with an identical automatic choke unit or you can do away with it and instead fit a manual choke over which you have full control !!
New from STR8, stylish new full body panels kits for Piaggio Zip SP mopeds.
Available in painted black or white
Finally a very stylish and affordable body panels kit for your Piaggio Zip moped. The kit contains all painted parts which are needed to replace all those nasty panels and give your bike a fresh new look for just £159.50 !!
A few months back Leo Vince announced the discontinuation of the Chrome plated version of the ZX, one of the most popular moped exhausts.
The chrome version of the Leo Vince ZX pipe was apparently being plated off-site by a third party, presumably not a cheap process- times are hard ! A shame, it was a very good quality and good performance exhaust, especially for standard 50cc mopeds and mildly tuned scooters with 70cc sports kits fitted.
The lacquered version was and is (at least for now) still being produced, but corrodes quickly unless constantly re-lacquered or painted.
Enter the Leo-Vince ZX-R last year, touted as a progression of the long standing classic ZX. But is it a progression in performance tuning refinement and quality, or an inevitable progression of cost cutting and marketing ?
First impressions are that apart from the chrome version being no longer available, some of the handmade tig welded sections from the original ZX have now been machine welded, presumably to keep costs down.
Here's a printout of a back to back runup we did of the ZX and ZX-R...
As you can see the ZX-R is essentially identical in performance to it's ZX predecessor. Any difference is so marginal it can be attributed to other factors and in reality it would seem the exhausts can be considered identical with regards to performance.
You can see comparisons of the Leo Vince pipes against other popular sports exhausts here
Given the current pricing of approx £120 for ZX Chrome and £100 for ZX non-chrome has never been cheaper (due partly to the arrival of its new ZXR 'successor') now would actually seem to be the perfect last chance to get your hands on a ZX Chromed pipe at a bargain price and with identical performance to the facelift ZXR version !
We still have substantial stocks of the chrome Leo Vince ZX left for Piaggio/ Gilera, Yamaha (Aerox, Jog etc.) and Peugeot (Speedfight etc.), but they won't last forever !
