This item originally appeared on the Myron's Mopeds webpage.
Moped Repair Tutorial
(Note: I am not the author of this tutorial. It was originally
written by someone calling themselves the 'Moped Guru'. I've place this
local copy on my site because I found it very helpful in working on mopeds,
but I cannot guarantee its accuracy. -JCN)
This guide is for mopeds only and will solve about 90% of the problems
people encounter when trying to fix their mopeds. If you own a scooter
that doesn't have pedals such as a honda express or vespa the following
manual doesn't apply, only motorized bicycles are covered here.
Before you begin:
All mopeds are metric, you will therefore need some basic metric tools.
This list describes some of the tools you may need:
- Socket size 8,9,10,11,12,13,14,16,18,20,22 mm
- Wrench sizes 8,9,10,11,12,13,14,16,18,20,22 mm
- Spark plug wrench
- Screw drivers (flat and philips)
- Carburator cleaner and penetrating oil such as WD-40
- Shadey Tree
Start Trouble Shooting Here.
All moped repairs begin with trouble shooting. The following outline
describes the most common symptoms.
- Engine doesn't turn over, Frozen, Siezed.
- No spark or weak spark.
- No fuel flow or insufficient fuel flow.
- Low power, doesn't idle properly, bogs on low or high rpm's,
If your moped falls into any of the above catagories, this manual will
help you get you 'ped up and running.
Step 1 Testing for spark and fuel flow.
Follow these instructions even if you think there is no spark !!!!!!
- Remove spark plug.
- Spray carberator cleaner into cylinder head as fuel.
- Install NEW spark plug and replace spark plug cap.
- Initiate starting sequence. (Peddle like hell.)
- Repeat if necessary to determine if engine runs.
Note: I have repaired a hundered or more mopeds using this guide line.
At this point one of two things will happen:
- If your moped runs until the carb cleaner is depleted and then
dies you need to check the fuel flow (go to Step 2).
- If your moped doesn't run you need to check for a strong spark
(go to Step 3).
Step 2 Checking for fuel flow. The most common problem!
The most common problem with mopeds is thay have been stored for a long
period of time with fuel inside. The fuel turns bad and clogs the bikes
natural fuel flow. In most cases the carburetor will need to be rebuilt
(or I should say cleaned) and the bad fuel drained, in some cases the
fuel turns into a varnish in which case you will need to flush out the
fuel tank and clean or replace the fuel valve as well.
Fuel flow in a basic moped is very simple. Fuel travels from the gas tank
through a fuel valve and fuel line to the carburetor where it enters a
float bowl. From there the fuel is sucked through a fuel jet by the
venturi effect and mixed with air and injected into the crank case (not
the combustion chamber but just behind the piston. This is how all
2-stroke mopeds lubricate the bottom end). From the crank case the
air/fuel mixture enters the cylinder head through a port that travels
up the inside of the head and is burnt, then exits through the exhaust port.
Back to Step 1.
- Remove fuel line from carburetor and check the fuel flow through the
fuel valve. Clean or replace the valve if necessary.
- Inspect fuel tank and flush if necessary.
- Remove and rebuild the carburetor using a solvent, like carburetor
cleaner. Do not use gas.
- Reassemble fuel system useing a NEW fuel line and filter.
- Test the brakes before you go flying down your driveway.
Step 3 Checking for spark.
There are about seven electrical components on the average moped ignition
system. they are:
- Spark plug.
- Spark plug cap and wire.
- High voltage coil.
- Contact breaker points.
- Kill/Run switch.
- Tail Lights ?
Now you may be wondering why I put tail lights on this list. Most people
wouldn't think that the tail lights would be on the ignition system but
they are. Much like on a car where the horn is on the brake light system
so you can test your horn to see if the fuse to the brake lights is working,
some moped engines won't run unless the tail light is working properly.
Step 4 Tail lights.
To test to see if the tail light maybe the problem.
- Install a NEW tail light or,
- Ground the tail light wire.
- Tomos mopeds ground the blue wire.
- Puch mopeds ground the blue/black wire.
- Peugeot mopeds ground the black wire.
Now go back to step 1 to see if this did the trick.
Step 5 Kill/Run Switch.
Mopeds don't have keys, they have kill switches. All the kill switch
does is ground the ignition system. Sometimes the wire or the switch
itself will become grounded. The test to see if the switch is the
problem is to simply disconect the switch from the system. It's best
to disconect it as close to the engine as possable. Follow the wire
from the switch down the frame to the engine and disconnect it.
- Remove the kill switch from the ignition system.
Back to step 1
Step 6 Contact breaker points.
Up to this point I have presented you with the most common problems
and their solutions so if you have gone through the first five steps
and your moped still doesn't run then it's time to test the points to
see if thay are opening. There are two ways to do this.
- Visuaily look at the points and rotate the flywheel until the piston
reaches top dead center.
- Electronicly with a ohm meter.
Back to step 1
Step 7 Spark plug cap and wire
If you have come this far and your moped still isn't running then it's
time to replace the spark plug cap and wire. The spark plug cap and
wire only cost a few bucks to replace and there's really no easy way
to test them unless you have a cap and wire that you know are good.
- Replace spark plug cap and wire with ones you know are good.
Back to step 1
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