Tech Talk with Mo!

Submit your tech questions to MO!

Proper installation of our roller sliders

Similar to the Dr. Pulley units shown in a GY6-150 variator.


If these are not installed correctly, the variator will not function, and speed will be limited.

Installation video here:


Hey MO! How do I know what engine I have? I have heard all this talk about 1PE40QMB and 157QMJ blah blah. It seems so darn confusing to get parts for these Chinese bikes! What can you do to help? -Lost in Las Vegas.

Chinese bikes and ATV’s can really be confusing, that is why scrappy dogs was started. There are two identifications to remember by using this site for help, not only to know what you have, but to get what you need. The first is the engine type. While this site uses a simplified directory at the left, you really need to know the engine number to get your parts right. This engine number is typically in two parts on the same stamp location. Most of the time the numbers are stamped on the left side of the engine, under the belt cover, near the front close to the engine mount to the frame. The bottom number is the reg. number, the top number is the one to pay attention to, this is the engine identification number. It tells you what you have. Below is a picture of a number plate for a 50cc 4stroke, also known as a 139QMB.

The engine number is very significant, and reveals alot. Take for example a popular engine, like the Honda Monkey (chinese copy) The number stamped on it is a 1P39FMB. The first number is the number of cylinders, the second, a P, is code for a horizontal engine. The next 2 numbers, 39, is the bore diameter in mm, 39mm bore. The next letter, F, indicates that it is natural (not forced) air-cooled style. The next letter designates that it is a motorcycle engine “M”. The next letter reveals the full engine displacement. B is code for a 50. C for a 60, D for a 70, F for a 90, G for a 100, H for a 110, I for a 125, J for a 150, and so forth. Notice that the size graduation increase is indicated by an increment in the alphabetical letter? It’s no coincidence. It’s amazing to me the cooperation in standards of China. There is also prefix letters on many, designating the manufacturer, like Quinjiang (we have them all on file), which stamps there acronym, QJ, as the first two letters in there code. It’s also very revealing, as the QJ139qmb is quite different then the other 139qmb’s. It uses the 1E40qmb (2T) transmission components, and the engine case is a little different. There are also suffix numbers at the end, which designate iteration levels, like -3 in the photo below, which denotes that it is the third design, or improvment.  Call or email us if you have any questions. We love to help. Here is the Chinese engine code chart with the example of the JOG 2stroke engine number 1PE40QMB-4

Some engines have the number plate on the upper rear side of the belt cover. GY6 engines are on the fron, bottom, left had side near the centerstand pivot. 2stroke JOG’s are near the rear wheel like Honda Spree elite and DIO. They are often on a sticker on the belt case. Sometime the airbox needs to be removed and alot of grime washed off on the 2strokes. By federal law they are stamped on the engine case and are there, even if you don’t see it at first inspection. Either way it will help you significantly to know this.  As far as the chassis body parts go, you can reference your body appearance to the listing shown in the Chassis directory given at the left, or simply click here- CHASSIS PARTS

This list is growing weekly, so if you don’t see your bike here, check later, or better yet use the Parts Finder form on the home page. Scrappy dogs are committed to making the Chinese vehicle market easy and fun for everyone, and affordable too!
Thanks for the question, hope your not so lost anymore.


AC vs DC fired or pulsed CDI IGNITION SYSTEMS

Hey MO! What’s all this I hear about AC and DC fired or pulsed CDI’S? – Harried in Henderson


Ok first the short answer. – Here is the readers digest of how a CDI works

In all cases there is a magnet that passes a magnetic coil and induces a pulse in that coil which then is wired to the CDI and causes the small induced pulse to fire an  electronic device (there are more than 1 type but this all happens inside the CDI)  Which discharges the larger pulse stored in a capacitor.  This larger output pulse is wired to the coil where the large pulse is able to make the coil function as a voltage increasing transformer thereby producing the very high voltage necessary to create a spark across the gap of the spark plug.

Now for the 2 main type of CDI used in the 49 cc scooter market,  AC and DC  Both function  essentially the same.  With the AC unit, alternating plus and minus varying voltages are used to charge the capacitor described in the paragraph above.  The DC unit takes 12 volts more or less DC from the battery and that voltage is used to charge the capacitor described in the paragraph above.

Pros and Cons:

AC unit allows the engine to run without the need for a battery or charging system of any kind.

DC unit was created to allow higher RPM ranges due to the instantaneous availability of the Charging current.  Where the AC one has lots of complex and difficult to explain things like coil flux density and residual decay etc.

The wiring is different also usually but not always, the ac ones have a rectifier or diode ahead of the CDI and the DC ones just connect directly to the battery.

The way to tell for sure is to turn on the key and see if 12v is present at the CDI assuming all else is correct.

Some units that are DC include:

Kymco Agility 50, Diamo Velocity, Vento Triton, Schwinn, Tomos, and other high end Chinese, Korean, and Taiwanese scooters.

One easy way to tell is the size of your CDI unit. The AC fired CDI will be much smaller than the DC fired CDI, as shown in this picture. Also, you have two plugs on the CDI, one with four, the other two. If the two wire plug actually has only one wire in it, it’s a DC. If it has two wires in it, it is an AC fired. The number of wires is only a loose guide. The size of the box, along with this guide is a better determination. An AC box will be smaller (see pic) and will measure about 1 1/2 by 2 1/2 approximately, the DC box will be much larger as it has a DC-DC converter in it. Such words as AC or DC pulsed or AC or DC triggered are the same thing as the AC or DC fired units.  One quick warning on performance units, with the advanced angle of our CDI’s your engine may actually run worse if it’s not running right or is carbureted too lean. I’d recommend installing a larger main jet to take full advantage of these units.Here is  somewhat simplified checklist to determine type:

Headlights turn on with key, DC.  Headlights turn on with engine,AC
Engine does not run without batter, DC. Engine runs without battery, AC
CDI box is pretty large, DC. CDI box is smaller, AC (note: our new digital DC units are smaller)
There is one wire on the two part plug, DC. There is two wires on the two part plug, DC.

Hope this helps. MO!

Here is a standard ignition circuit for a chinese scooter. Note that the red wire from the stator to the CDI will not be on a DC fired system. The kill switch wire will instead be the positive power source from the igntion key switch.

MINARELLI 2STROKE PISTON PIN SIZE DIFFERENCE , 10MM vs 12MM and variator size difference

Hey MO! How the heck do I know if my Minarelli based engine has a 12mm or 10mm wrist pin, without taking it all apart first? – Confused in Chicago


Our knowledge database is growing, but we know a few things. Adly’s and Hammerheads are 10, so are the Italian Minarelli engines like Malaguti, Italjet, Beta, and Aprillia. The 12mm pin is found on later CDI’s, chinese JOG-2T, Vento Triton. These engines are poplular in 2-stroke full size scooters and ATVs such as Malaguti, Yamati, United Motors X-Speed, Aprilla, CPI, Benelli, Vento, Eton, Adly and many more. Italian made units tend to use 10mm pins (Chinese JOG 2T clones tend to use 12mm) please measure and check before ordering. Certain brands such as CPI / United Motors / Muz older models used 10mm newer post 2004 use 12mm. All Italian made models use the 10mm such as Aprilia / Malaguti / Italjet that are Yamaha Minarelli based.

Probably the most accurate, without complete disassembly, is to measure the inside diameter of your variator pulley. If it is 21mm, your wrist pin is 12mm. If it is 18mm, your wrist pin is 10mm. You can also count the number of splines on the outer variator face where it mates with the crank. The smaller 18/10mm crank has 17 splines, the larger 21/12mm crank has 15. The larger crank was originally designed for the JOG90 engine, but comes in 50cc too. Also, don’t confuse your Minarelli 2stroke with the Franco Morini type two stroke found in TGB R5 Laser, Key West, 101S, the Suzuki Address, and some Italjets. These kits are also available from Scrappydogs, as they are authorized dealers for TGB products.

Hope this helps. MO!

Here are our Minarelli based parts link.  Minarelli

Variator roller weight choice

Hey MO! I want to get some more speed out of my scoot, but I don’t want to spend much money. I’ve heard that by changing the variator roller weights you can do this the most economically. Is this right? and if so, what weight should I go with?        -cheapskate in Baltimore


Yes, rollers are an economical way of increasing performance, however, it comes with a compromise as any performance upgrades do. The over simplified explanation that is very common is that heavier weights give you more top speed, and lighter weights more take off. This is true to a point, but not really. The variator weights control what is called the “constant engine speed”. I’m sure you’ve noticed when you give your scoot full throttle it holds a certain engine speed while the vehicle accelerates. The variator controls this engine speed. If your engine is above it’s maximum torque because of too light of of weight, it will not accelerate like it could. If your engine is below it’s maximium torque because of too heavy of weight, it also will not accelerate well as it will bog.

So, this being said, you can actually gain top speed AND acceleration by lightening the rollers. This is true for a number of reasons. Your engine has a certain engine speed, RPM, that is it’s most powerful and most efficient, this is called the torque peak. You cannot get maximum performance without being at this RPM. Second, remember that the variator get to it’s maximum contraction almost immediately upon acceleration, and holds there, it’s the rear pulley that slowly contracts as rear wheel speed increase, thereby increasing the ratio between engine and wheel, making for more road speed.

To conclude and simplify: lighter rollers increase the “constant engine speed”, and heavier rollers decrease it.