Easy - Requires little knowledge of your scooter and few (if any) tools
Medium - Requires some mechanical knowledge and a decent selection of tools
Difficult - Requires in-depth knowledge and specialized tools
In all cases, it would really help to have the service manual for your scooter.
Individual maintenance tasks
Flywheel (rotor) disassemblyThis is the part in the engine (usually located under a case on the RH side of the engine) that rotates to generate electrical power when the engine is running. It is a flywheel with a few strong magnets inside. Removing it is a snap with an impact wrench and the proper flywheel puller. If you don't have an impact wrench, use a strap wrench or a flywheel holding tool to hold the flywheel as you remove the flywheel nut. Then take a rubber mallet or a piece of 2 X 4 and wap the wrench. That impact action will loosen the nut. You'll really have a hard time if you just try to twist the nut loose. If you don't have the proper flywheel puller, you should be able to get the flywheel off with a good fitting gear puller. If the puller doesn't fit well, you risk damaging the flywheel. Once you have the bearing out, you can take it to the local bearing supply house. They will be able to match the numbers on the bearing to a suitable replacement part. Most of the new bearings seem to be double sealed (the bearing has dust covers on both side). The OEM bearings are usually sealed on only one side, or not sealed at all. The seal serves to keep dust and dirt out of the inner workings. All three types fit the same. When installing the bearing, it helps to put it in the freezer for a few hours. It will contract a bit and allow for an easier install.
General electrical informationUnderneath the rotor is the stator and usually a pulse generator. The stator consists of a few coils of wire. The spinning magnets in the flywheel interact with the coils to generate A/C current. The current then flows to a rectifier, which convers it to useable D/C current. Most rectifiers also act as regulators. The regulator will control how much current flows to the battery. At high engine speeds and low electrical loads, more current will be generated than can be used. Usually excess current flows to the battery to recharge it, but too much current will wreck the battery. In this case, the regulator will re-route the current to ground.
The pulse generator creates a small pulse of current, which is sent to the black box (ignitor). The ignitor controls the timing of the signal and sends it on to the ignition coil. The ignition coil converts this small flow of electricity into a large spark that is generated at the spark plug.
The starting circuit consists of the starter switch on the handlebar, the kill switch on the
handlebar, the brake switch (usually the rear brake), the starter solenoid, and the starter.
When you turn on the key and press the starter switch, a 12V signal will be sent to the
solenoid assuming the starting circuit is complete. It will only be complete if the kill
switch is set in the "Run" position, you have depressed the brake, and you have the sidestand
up (on some scooters). The solenoid is merely an electrical switch that handles the large
amount of current needed by the starter. It has two little terminal connections and two big
ones. Apply 12V to the two little connections, and the solenoid will complete the circuit
between the big terminals. Usually there is an audible click when this happens. The completed
circuit between the big terminals will route power directly from the battery to the starter.
Is my engine worn out? Carb function
Regular and frequent oil changes with a high quality oil will go a long ways toward making your engine last. Periodic valve adjustments and air cleaner replacement/cleaning are also important. Lastly, don't forget to change the spark plug at the required intervals.
So what exactly wears out in the engine? In two strokes, the piston and cylinder will wear. They also wear in four strokes, just not as quickly. As the wear occurs, combustion gases will leak by the piston and piston rings. Oil from the crankcase will also leak by, and be burned up along with the fuel. This oil burning process depletes your oil supply and leads to a bit more pollution. Worn valves also allow combustion gases to go where they aren't supposed to go. The fuel/air mixture is not drawn completely into the combustion chamber, and exhaust gases are not completely withdrawn. This leads to starting difficulties, poor idle, and sluggish performance which will get worse over time.
A great test of an engine's health is the engine compression. An engine is really just an air pump. When it starts wearing out, it doesn't pump as well. When an engine is new, compression could run anywhere between 100 psi - 200 psi. Two strokes will have lower engine compression because they have lower compression ratios than four strokes. For instance, say a two stroke has a compression ratio of 7:1. This means the volume at the top of the piston stroke is 1/7 the volume at the bottom of the stroke. If you multiply 7 times the atmospheric pressure of 14.7 psi, you get an engine compression of 102.9 psi. So allowing a bit for losses (after all the seals aren't perfect in the engine), 100 psi is a good number. A four stroke with 13:1 compression should ideall have 191 psi on engine compression. Be sure and check compression on a warm engine with the throttle held wide open, so you can get the best reading.
Besides the piston/cylinder/valves, the parts that wear are the bearings. This includes the main bearings on the crank (these are either plain bearings or roller bearings - roller bearings are better) and rod bearings on the top and bottom of the rod. Two stroke scooters also have crank seals that must be in good shape. Depending on the wear and the quality of the components, some or all of these things must be replaced. For instance the big Yamaha scooters have very good quality main bearings. As the engine ages, you should be able to get away with just doing a top end job. This means you don't have to take the engine completely apart and replace the bearings. You should be able to get away with resurfacing the valves and replacing the piston (after a re-bore job).
Three circuits control air flow: the air-screw, the throttle slide, and the air jets. Four circuits control the fuel: the pilot/slow jet, the needle jet, the jet needle, and the main jet. The different air and fuel circuits change the carb jetting for the different throttle-opening positions as follows:
Is my engine worn out?The first question is - how long do scooters engines last? That's kind of a tough question. How long do automobile engines last? The answer of course is that it varies by size of engine, how hard you ride the scooter, how well you maintain the scooter, and how well the manufacturer made the engine. It could last anywhere from 5,000 miles to over 100,000 miles (in the case of well maintained Helix engines, for instance). Smaller engines like 50's and 80's have to work harder, and they run at higher RPM's to get around. So they will wear out faster. In two stroke engines, the piston and cylinder have to do more work. So the pistons wear out sooner. In four strokes, you have to worry about both the piston and the valves.
Carb functionA carburetor is a complicated device that performs a simple function - delivering the correct fuel / air ratio to the engine. Your carb mixes fuel with air in a precise ratio over a wide range of throttle and engine temperature settings. Carburetor jets are calibrated orifices that take the form of parts such as pilot (slow) jet, pilot air screw, throttle valve/slide, jet needle, needle jet, air jets, and main jet. Fuel jets have matching air jets. If an air jet gets clogged, the fuel jet will not be able to flow fuel because it cannot create a vacuum to draw the fuel. Fuel jets are available in many sizes to fine-tune the air-fuel mixture to the optimum ratio. The jets and the passageways are tiny! Just a small amount of water, dirt or old gummed-up fuel can get trapped in the tiny passages of the carb and cause havoc with jetting or even lead to engine damage. In most cases, you'll have to disassemble the carb to clean it properly. Spraying carb cleaner into the airbox just will not clear the passages properly. Sometimes you will have to run a wire or a small drill bit (being careful not to damage the jet) through the jet to clean it.
Tuning for performanceBecause of the volume of information I would like to present, this section will eventually have its own web page.
Clutch disassemblyThere is some energy stored in the large spring behind the clutch, but it can be disassembled without too much trouble or safety risk. My technique is:
General electrical problem diagnosisWhen you're faced with a problem, try to narrow down when it occurs. Most often, the wiring itself is probably ok. Under rare conditions, a wire will become chafed by rubbing against the frame or a sharp corner. Most often the problems occur at the wiring connections. The connections can come loose or get corroded.
For instance, say your horn just stopped working. It is probably a bad horn or a dirty horn
switch. I try to start with the easiest thing to check. In this case I would first test the horn
to see if it's working. Unhook both of the wires going to the horn and apply 12V (or 6V if you
have a 6V system) directly to the horn terminals. Does the horn work? If so, check the condition
of the terminals on the horn and on the wires leading to the horn. Are the clean and shiny, or
dull and dirty? A small wire brush will clean them in no time. Next, I would take apart the
Are the contacts clean? Even if they're clean, I work clean them with contact cleaner
and a brass brush (see the next tip below). Turn on the key and connect the wires together. Does
the horn work? If the horn still doesn't work, you'll have to trace the wires. Look for corroded
or broken connections.
Blinkers not working Electrical gremlins in your switches Light bulbs
Blinkers not workingIf only the left or right side blinkers aren't working, it is most likely a problem with a bulb. The blinker relay needs the resistance of both light bulbs to work properly. If only one bulb is lighting up, check the other bulb to see if it is bad, or badly corroded. A corroded bulb can be cleaned with a wire brush. A corroded light bulb socket can be cleaned very nicely with a 1/2" copper pipe cleaning brush , found at your local hardware store. If neither side works, suspect a dirty blinker switch or a bad blinker relay. Check for 12V going into the blinker relay. The relay is the part that actually makes the blinkers blink. On the older (mid 80's scooters) it is generally a mechanical device. On newer scooters it is generally an electronic device, which is more reliable and less subject to corrosion. On the mechancial relays, there is an electromagnetic switch and a cantilevered wire. The wire heats up as current flows through it and it bends, breaking contact with the circuit. This turns the blinkers off. Then it cools and moves back, making contact and completing the circuit again. The relays get corroded and stop working over time. Replace the relay with a new one. If you don't care about getting the stock relay, a good and inexpensive replacement part can be found at your local auto supply store. If you have sufficient voltage going into the relay, then it's probably bad. If you don't, then check your blinker switch. You can clean the switch as per the instructions below.
Electrical gremlins in your switchesBlinkers suddenly not working? Starter switch not working? More often than now, these problems can be traced to gummed up or dirty switches. Over a numbers of years, dirt and crud get into the electrical contacts and prevent them from working. The cure is a bit time consuming, but not difficult. A quick and dirty fix is to spray a bunch of electrical cleaner into the switch while you work it back & forth. This may solve the problem, but in general you'll have to disassemble and clean the switch The fairing / speedo area will have to be disassembled enough for you to get the switches out. Once you have the switches out, you'll find several wires, springs, ball bearings, and electrical contacts inside. Be sure and note how these parts are put together so that they can be reassembled properly. Carefully disassemble each switch in turn. Ideally, you would do the work over a blanket or a large rag to help prevent lost parts. Clean the copper contacts with electrical contact cleaner and a small brush. It is best to use a brass brush because it is softer than a wire brush and won't damage the contacts. I use a small dab of dielectric grease (available and any auto store) to ensure the moving parts slide smoothly. Upon reassembly, you'll be pleasantly surprised how nicely the switches work!
Light bulbsThe common sizes on 12V scooters are:
|Combination brake / tail light (two filament bulb)||1157||12||27 / 8|
|Turn signal (slightly brighter)||1034||12||23|
|License plate light||158||12||8|
|High beam indicator, oil light indicator, etc.||158||12||3.4|
|Combination brake / tail light (two filament bulb)||1154||6||21 / 5|
|High beam indicator, oil light indicator, etc.||63||6||8|
The SAE number is from the Society of Automotive Engineers, and is just a standard designation for the bulb. You can find most of these bulbs at your local auto or motorcycle shop, by the SAE number. In a pinch, you can use a 12V bulb in place of a 6V bulb. It won't burn as bright, but it will work (and it will last longer). If you put a 6V bulb in where a 12V bulb is needed, the 6V bulb will burn very brightly for a minutes and then it will burn out.So, you'd like to put in brighter bulbs? And you would especially like to replace that 50 watt bulb headlight with a 100 watt bulb? In general assuming light bulbs with the same efficiency, the brighter bulbs require more power. This can be a problem if the wattage is too high. It creates two problems 1) the greater heat of the higher wattage bulb can melt the bulb fixture or the wiring 2) the higher load may overwhelm your charging system and end up draining the battery when you ride. Quite a few scooters (especially the 50's) have charging systems that are just barely adequate. If you have a 50, you may notice the lights are dim at idle. The lights brighten as you rev the scooter because the charging system puts out more amperage. In cases like this, the battery is being drained at idle because the charging system is not putting out enough power to cover the power needs of the scooter. As a side note, the charging system draws a bit of power from the engine. If you have higher wattage lights (or you add a radio or something), your engine will have to work a bit harder to supply the needed current. You have to be careful when replacing a standard incandescent bulb with a halogen bulb. While the halogen bulb is more efficient (you get more light for the same wattage), it gets much hotter due to the nature of the bulb. It might melt your fixture and the surrounding plastic in a big hurry. A good alternative that is just coming on the market are the super bright LEDs. These little lights consume very little power and are very bright for their size. They will last 10 years or more - over 5 times as long as a regular bulb. They also produce very little heat and they light up quicker. This is a nice safety feature when used in your brake light, allowing the traffic behind you to see your brake light is on a little sooner than with a standard bulb. Packing 5 to 40 or more LEDs in a bulb makes it bright. The only downside is that they are still expensive - around $10 to $25 for the best bulbs.
Broken speedometerSo your speeo doesn't work? Here are the likely culprits, in order of occurence:
Steering head bearingsMost scooters use loose ball bearings in the steering head. Smaller scooters (50's and 80's) tend to use 5/32" bearings. Larger scooters use 3/16" bearings in the top of the steering head and 1/4" bearings on the bottom (this is where most of the weight is carried). If your front end wobbles upon deceleration, then all the steering head probably needs is a little tightening. If the front end does not move smoothly as you turn the bars, or if it feels stiff and "notchy", you'll probably need to disassemble and repack or replace the bearings. The good news is that these ball bearings are very inexpensive and easy to find at your local well stocked hardware store.
Sticking brake leversMost of the time the problem is either the brake cable or the brake pivot at the brake hub. Loosen the brake cable adjuster at the brake arm on the hub. Try to move the arm by hand. If it moves freely, your cable is bad. If it doesn't move, you'll need to disassemble the hub and grease the pivot. Sometimes you can bring a sticking or rusted brake cable back to life. Remove the cable and gently place it in a vise vertically, with the end of the cable at the wheel facing up. This end of the cable picks up dirt and water from the road. Does the cable move at all? If not, you are definitely better off just replacing the cable. They are less than $20 in most cases. I have never been able to fix a badly rusted cable. Start dripping some light motor oil in the joint between the inner and outer cables. Work the cable back and forth while you do this. It's a tedious process. Try it for 10 - 15 minutes and see if the cable is working any better. If so, you might be able to salvage it. The easiest way to fully lube the cable is to tape a small bag just below the joint. Fill the bag with some motor oil and let it sit for a day or so. You should see some oil dripping out the bottom of the cable. Other possible causes are: broken brake spring, badly rusted brake hub and brake shoes, a misrouted cable, or a dirty brake perch (the thing that holds the brake lever to the handlebar).
Plastic repairJust about every used scooter I have ever owned (probably around 100 of them) has had cracked body plastic somewhere on the scooter. Body plastic is made of different types of materials - ABS, PVC, etc. Repairs can be made using fiberglass repair kits, bondo, various glues, and by plastic welding. The fiberglass repair kits are quite strong, and will work well on all types of plastic except ABS. ABS is generally too flexible so the repair will not hold.
Fuel petcockThis is the thing that controls the flow of fuel from the gas tank to the carb. Most of the time, it is located on the underside of the gas tank. This used to be a lever that you would have to manually turn on and off. If you forget to turn it on, your scooter will die after a short distance. Virtually all modern scooters have a petcock that works automatically. It is controlled by a vacuum line that attaches to the carb or the intake manifold. When the engine is spinning, a vacuum is drawn on the line. This will move a rubber diaphram in the petcock, and allow fuel to flow through the petcock. As soon as the engine stops spinning, the vacuum will stop. Then the fuel flow stops. Cool, huh? As petcocks age, they can stop working. In order for the petcock to work properly, it must do at least 3 things:
Sticking throttle cablesThrottle cables are not subject to the same weather abuse as brake cables (as noted above). They usually stick because of a worn cable, binding throttle housing, misrouted cable, or a stuck carb (either a stuck vacuum piston or throttle cutaway, depending on the type of carb).
Rusty gas tanksThere are several ways to clean your tank. First, I'd try to determine how badly the tank is rusted. Is it just surface rust? You might be able to just live with the rust if it is light. Or is it really bad (pin holes allowing gas to leak out of the tank)? If it's really bad, you might want to just replace the tank. Pinholes can be repaired with the products mentioned below, but it's a fair amout of work. In a nutshell, you can remove the tank and:
My scooter won't start or has poor performanceI get this question a lot. It could be many things. First, ask yourself:
Tire maintenanceMaintaining your tires is important. They are the only thing holding your scooter to the road. To give you an idea of their importance, imagine you had no tires and you had to ride you scooter on its rims. Braking and cornering would be almost impossible - just trying to ride it would be difficult enough.
ToolsThis is a fun subject for me. I like having the right tool for the job. It makes things go faster, easier, and much more enjoyable. My dad taught me to buy QUALITY tools. They look better, feel better, do a better job, and last longer! I have a few seldom-used tools that are cheap and made in China. Not to start a fight or anything, but most of the stuff from China is not good quality. It's like the Japanese stuff we used to get in the 60's (yea I remember back that far). Hopefully it will improve. The design is ok, but the quality of the materials is generally poor. Also fit and finish are poor, as are the manufacturing tolerances. So they are not enjoyable to use and they don't work as well as quality tools. Stick with the quality brands and you will never be disappointed. There are so many Chinese and other poor quality brands that they cannot all be named. Try to use price as your guide. If it's not a quality brand and if you can get a 50 piece socket set for $10, you don't want it :>)
Torque settings for fastenersUndertorquing and overtorquing are both bad. The problem with Undertorquing is obvious - you're going to loose that nut or bolt because it wasn't tightened enough.
Two-stroke tuneupsWith no valves to worry about, tuning up a two-stroke is very easy. Just replace the spark plug :>) The spark plug is more critical to good operation in a two stroke, and they tend to wear out faster. I'd replace them every 2000-3000 miles. Also, be certain that you are using the proper injection oil! Do not use automobile oil - you'll ruin the engine. It must be oil that is specifically designed for two-strokes. The bottle should say something like "for 2 cycle oil injection" (two cycle and two-stroke mean the same thing). If you don't have oil injection, but sure to properly pre-mix your oil and gasoline. I've done this for years with dirt bikes. It's a bit of a pain, but not difficult.
Over time, the exhaust pipe can get clogged up with oil and carbon residue. It will happen less frequently if you use a good quality injector oil. Here are some ways to unplug the exhaust pipe (in order of difficulty):
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