General Troubleshooting and Tune-Up Guide

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GENERAL MOPED TROUBLESHOOTING and TUNE-UP PROCEDURES

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The 3 most common reasons why mopeds don't run are....

1... dirty carb (inside)

2... dirty, worn, or mis-adjusted ignition points.

3... fouled spark plug.

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BASIC TROUBLESHOOTING (follow these steps to get it to run)

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The first thing to check on a moped that won't run is to see if you have spark at the spark plug.

Pull the spark plug out and hold the metal part of the plug firmly against the cylinder head while you kick or pedal the moped rapidly with the key and switch on.... it might help to do this at night or in a dark garage to make it easier to see the spark.... it might also help if you have 2 people... 1 to pedal/kick, and 1 to hold the plug firmly against the cyl. head... you are looking for a blue spark to jump the gap on the plug.

Make sure you have a good spark plug to start with, a black or gunky or wet one will not spark.

It is smart to just buy a new plug to start with.. you can always save it for later if the old one turns out to be good.

(working for hours only to find out it was a bad plug is frustrating)

If there is no spark.... clean the ignition points (like it says below)

If there is spark... squirt a little bit of gas (like a spoonful) into the spark plug hole and try to start it.....if it starts and runs for 5 seconds and then dies, then check for fuel flow to the carb (like it says below)

If you have fuel flow to the carb and spark at the plug and it still won't run.. then clean the carburetor (like it says below)

If you have done all those and it still doesn't run... go to the part that says... What Else?

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GENERAL TUNE-UP

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FUEL FLOW to the CARBURETOR

Remove the fuel line going into the carb.. turn the gas on.. does fuel flow freely out the gas line?.. No?.. You may have a vacuum operated petcock (if you do there will be another rubber line going from the engine to the petcock).. take this second line off the engine or carb and suck on it and watch for fuel flow out of the other line... If no flow, you must take the petcock off and disassemble and clean it..

CLEANING the CARBURETOR

Clogged or dirty carburetors are the most common reason for poor performance.

The parts of the carb that are dirty or clogged are the small holes inside the carb (air and fuel passages).. not the outside.

The carburetor must be removed... then you take off the float bowl (on the bottom)... then you remove the brass "main jet" in the middle of the carb... try to blow air thru it ... now hold it up to the light and look thru it... it must be clean and clear.... if it is not clear you must poke a piece of fine wire thru it.... a wire plucked from a wire brush works good.... or some soft multistrand copper wire like from speaker wire or lampcord wire... don't use a drill bit, it might damage the brass or make the hole too big.

Next you should screw the idle mixture screw in.... (Before you screw it in...look at where the screwdriver slot is at... then count how many turns it takes to go all the way in... like 2 1/4 turns, or whatever)..... then remove it and all other screws..be careful.. don't forget where everything goes.. and don't lose anything!

Now you must clean out all passages in the carb with aerosol carb cleaner and compressed air... (like 100 psi)... with a blow nozzle... squirt the cleaner in ALL THE SMALL ORIFICES one by one followed by a blast of compressed air.... while you are blowing air thru the holes feel with your fingers to feel where the air is coming out of and blow the other way too.... do this SEVERAL times.... then reassemble all the parts.

Remember to turn the idle mixture screw back out to its original setting... usually between 1 and 2 full turns out from all the way in) and reinstall the carb.

The IGNITION

Older engines have "breaker points" ignition.. which can get dirty, wear, and need adjusting occasionally.

You will find them by looking through holes in the flywheel.. (usually on the left side of the motor)

Newer motors don't have points.. they use an electronic ignition called a CDI.. and there is nothing to clean and set.. but you can still check the timing with a strobe light.

CLEANING the POINTS

You can clean them through the holes in the flywheel..(you don't need to remove the flywheel)

To clean them you need some sand paper (use 400 grit wet and dry sandpaper), a piece of clean paper, some scissors, and some aerosol brake cleaner or carb cleaner and some compressed air with a blow nozzle.

Remove the ignition cover and look for the points in one of the holes in the flywheel.... lay the bike over on its side and sit on a milk crate or something to get comfortable.

Then cut some thin strips of sandpaper (like 1/4" wide, 3" long).... pry the points open with a small screwdriver and stick the piece of sandpaper in between the points and let them close.... then pull the sandpaper out.... do this SEVERAL times to each side till they are smooth.... now pry the points open and blow them off with compressed air... then spray them with the cleaner.... then cut a strip of the clean paper and pry the points open again and drag the paper thru a few times (the paper should come out clean and should drag through smoothly).... blow them off again with air while open.... now they should be good.

WHAT is IGNITION TIMING ?

Correct ignition timing means the spark plug is firing at the correct moment in the engines rotation.. a little before TDC (top dead center.. when the piston is closest to the spark plug).

The spark plug fires the instant the points "break" open.

You want the points to open when the "F" mark on the flywheel lines up with the mark on the engine case.

Look on the outside of the flywheel for some lines and letters.. there should be a T mark next to a line... and an F mark next to a line... There should also be a mark on the engine case .. the T mark will line up with the mark on the engine case when the piston is at TDC.

To find the mark on the engine case.. you can remove the spark plug and stick a screwdriver in the hole against the piston and turn the flywheel.. when the piston pushes the screwdriver the farthest out, the T mark will be lining up with the mark on the engine case..

The points should have already opened BEFORE that.. they should just START to open when the F (Fire) mark lines up with the mark on the engine case.

To check this accurately you would need to have special tools.

CHECKING and SETTING IGNITION TIMING

You check and set the timing with the flywheel ON (you don't remove the flywheel)

Clean the points like it says above FIRST.

There are 2 simple ways to set and check timing.

>>>>> The easiest is by setting the point gap.

It is not real accurate.. but it is usually good enough for a ped motor to run OK.

To set the gap you just rotate the flywheel near where the F mark and the engine mark line up.. while watching the point gap.. wait till the gap is at its biggest.

You want this gap on most peds to be about the thickness of a thin piece of cardboard.... about .015"...or (.4mm)

They sell "feeler guages" at a tool store to check this gap... or...

or a macaroni and cheese box is........... .018"

or a Girl Scout cookie box is............. .016"

or a breakfast cereal box is about........ .016"

(..I just measured them !..)

So if you cut a thin strip of one of those you can use it as a "feeler guage".

Then you LOOSEN the small screw that holds the small point's set down.

And then you can pry the points set around with a screwdriver in the "pry notches" they have... the gap will get bigger or smaller depending on which way you move it.

You want to adjust it so that the cardboard slides in and out nicely.

Not too tight.. not to loose.

Now tighten the screw back down.

Now check the fit again... because tightening the screw can change the gap.

Sometimes you have to do this a few times to get it right.

You have just set the point gap to get the timing close.

>>>>> A more accurate way to set timing is by ignoring the gap and doing the "rolling paper test".

For this you need a very thin piece of paper (like cigarette rolling paper..or a cigarette pack piece of cellophane)

All you do here is put the thin strip of paper between the points... and keep light tension on the paper (like as if you are gently trying to pull it out) while watching the F mark and the case mark as you slowly rotate the flywheel with your other hand.

Remember you are rotating the engine in the direction it normally travels (CCW as viewed from the left side of the bike..CW as viewed from the right)..

....The paper should slip out just as the points start to open when the F mark lines up with the case mark.

..So.. it's...one hand on the flywheel.. other hand on the paper...eyes on the F mark.

If the paper pulls out too late.. you will have to move the points for a larger gap.

Too early.. move the points for a smaller gap.

(NOTE.. If a tiny piece of paper tears off and stays in the points... You will get NO spark... pry them open and blow them out)

>>>>> You can get MORE accurate by using electronic equipment to tell exactly when the points open.

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......... OK.... WHAT ELSE...?????

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... I've checked for fuel flow to the carb

... I've cleaned my carb THOROUGHLY

... I've cleaned and set my ignition points

... I've got a fat blue spark at a brand new plug

But my moped still won't run... or it runs like crap

........... Why ?? ..........

Some common reasons why.

... The muffler is clogged with carbon

... The exhaust port is clogged with carbon.

... The air filter (going into the carb) is too dirty to flow air very well.

... The air filter is missing, and the engine is getting too much air.

... The rings or cylinder are worn out or damaged and don't have enough compression.

... Your head gasket is leaking.

MUFFLER CLOGGED with CARBON

A moped whose muffler is clogged will usually start and run... but will not run very fast.

To test to see if this true with yours... remove the muffler and run the ped without the muffler... (it will be loud).... if your ped picks up a lot of speed... then it is probably clogged.

To unclog it you need to get it real hot and burn it out... one way is to attach a coathanger wire to it and set it into the coals of a hot campfire... pull it out every 5 minutes or so to make sure it is not melting it... turning orange is OK... melting is not.

You can also unclog it with an oxy-acetylene torch by warming up the outside till it is orange hot and them blowing flame down into the pipe and pulling the oxygen trigger.... only do this if you know what you are doing... you could damage the pipe badly if you don't.

EXHAUST PORT is CLOGGED with CARBON

Same as a clogged muffler... it will run but not very fast.

To check this.. remove the exhaust pipe and look into the exhaust port (on the cylinder)... lay the ped over on its side to get a good view.

You should be able to rotate the ignition flywheel with your hand while looking into the port and clearly see the piston going up and down.

If you can't... you need to remove the head and cylinder and thoroughly scrape out the exhaust port.

AIR FILTER

Engines are designed to run with air filters to keep dirt out so that the piston and rings and cylinder will last a long time... if the air filter gets clogged it will richen up the air/fuel ratio and slow it down, maybe foul plugs, and maybe cause the engine to "four-stroke".

Foam air filters can be cleaned in gasoline and allowed to dry... then LIGHTLY be oiled (just use a little and try to spread it around)

Paper filters can be blown off with compressed air (or buy a new one)... use no oil

Pleated cloth ones (in a wire gauze..like the K&N brand) can be cleaned in gasoline and be LIGHTLY oiled with light oil (like ATF)

Running with no air filter can cause the engine to get too much air and lean out and possibly seize.

If the engine runs a lot faster with no air filter then your main jet is too big (and many of them are too big... especially Euro peds)

WORN OUT RINGS and CYLINDER and PISTON

.........(test for compression).........

A quick way to do an easy test for this is to remove the spark plug and have someone kick or pedal the motor rapidly while you hold you finger or thumb FIRMLY over the spark plug hole.

...You must wiggle and squish your finger down on the hole and your finger must be big enough to TOTALLY cover the hole, push hard.

.. The piston and rings should compress the air enough to blow your finger right off the spark plug hole.

..If it doesn't blow your finger off the hole then your compression is low, and you need to remove the head and cylinder and look for the reason why.

Look for scuffing and scoring on the cylinder and piston skirt.

Or it might have had a seizure and smeared aluminum from the piston on the cylinder and even smeared melted aluminum over part of the rings.

If there is no scuffing and scoring and there is no evidence of a seizure and the moped has over...say... 5000 miles on it with the same rings... buy new rings and install them correctly.

If there is heavy scuffing and scoring in the cylinder... then you need to buy an oversize piston and rings and have the cylinder bored and honed to fit them.

INSTALLING PISTON and RINGS CORRECTLY

Everything should be cleaned very carefully before you put a new top end together.

Dirt now will ruin parts very quickly.

You should also smear the piston and cylinder with 2 stroke oil fresh out of the bottle.

The piston is only supposed to go in one way... It should have an arrow on the top which is supposed to point at the exhaust port.

Rings are usually supposed to be installed one side up... they usually have some very small letters on them which go on the top (towards the spark plug).. look very carefully.

Next you have to locate the ring end gaps correctly on the piston... look in the piston ring grooves... you will see a small pin in the groove... the ring ends go right at those pins... (if you have 2 rings the pins are NOT in the same location for both)

Look closely at the ring ends and the type of the pin and you will see how they mate together.

LEAKING HEAD GASKET

Some mopeds don't use a head gasket....Most do.

The head nuts should be tightened correctly.

You can sometimes hear compression squeezing out past the head gasket... pfft... pfft... pfft.... Or look closely between the cylinder and head to see if it is oily... this usually indicates a leak... Or remove the head and gasket a look for black traces of soot on the surfaces of the gasket or head or cylinder.

Head gaskets on 2 stroke mopeds are made of metal (usually aluminum...sometimes copper).

Metal head gaskets can be reused over and over as long as you didn't damage them by bending them badly.

I would not recommend a gasket made of all purpose gasket material.

That is similar to paper and is not made to withstand the heat and pressure of combustion.

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GENERAL MOPED INFO

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GAS and OIL and TWO STROKES

Most mopeds have 2 stroke engines.... 2 strokes consume oil for lubrication.

Newer mopeds might have an auto-lube oil pump.. so that you don't have to pre-mix the gas and oil.... For older mopeds you will need to "pre-mix" the oil with the gas.

How to tell ??... If your ped has a gas tank AND an oil tank... it has an autolube oil pump.

If it only has a gas tank.. you have to premix.

OIL

With modern 2-stroke oils you should probably pre-mix between 3 oz.(43 to 1) or 4 oz.(32 to 1) of oil per gallon of gas.

Make sure you buy 2-stroke oil.

Some people say synthetic works better... But I have found regular 2 stroke oil to be just as good as the much more expensive synthetic oil..

GAS

Mopeds are low performance engines designed to run on the lowest octane of gas you can buy (87 oct.) because they are afraid that somebody who doesn't know better will put the cheap stuff in..... and higher octane will not make it run better or faster or make more power.

But higher octane will not hurt your engine either.

GAS TREATMENT

Unless you have modified your engine for higher compression, you don't need these additives >>>

octane booster

lead additives

racing gas

They are a waste of time and money.

But I do put a little gas treatment in the gas every once in a while.. because moped carb jets are so tiny that they get clogged easily...the gas treatment helps dissolve stuff in the gas that might clog these jets.

I use one capfull of gas treatment per moped tankful (but you won't hurt it if you miss a tank now and then).

You buy the gas treatment at a gas station or Auto parts store.

FUEL FILTER

Since mopeds have such small carburetors.. they get clogged easily, and you should get an inline fuel filter and install it in the fuel line going to the carburetor...

Install the filter so that the fuel is flowing in the direction of the arrow they put on it.

You can buy one from a motorcycle shop.

.......Fred......... Mar 19, 01....... Rev #5..............

Re: General Troubleshooting and Tune-Up Guide

I would not recommend a gasket made of all purpose gasket material.

That is similar to paper and is not made to withstand the heat and pressure of combustion.

this is not always true, i made a head gasket out of bristle board that was oil socked and it lasted a week of driver almost non-stop

Re: General Troubleshooting and Tune-Up Guide

Ron Brown /

Fred,

Now that you are into re-using copper gaskets, you may want to mention annealing. Heat the gasket to cherry red then dunk in cold water. You now have a clean, soft copper gasket which will seal much better. Works for exhaust washers and drain plug washers too, but only for copper.

Ron

Re: General Troubleshooting and Tune-Up Guide

#CrazyWayne™ rocks. #CrazyWayne /

Bump for the nubs

Re: General Troubleshooting and Tune-Up Guide

Only three original posts!?

This thread needs this link: http://www.mopedarmy.com/wiki/Fred%27s_Guide

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