General Moped Troubleshooting and Tune-Up Guide

....Use this guide to get your moped running... or running better...




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.


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


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)





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.. If no flow, you must take the petcock off and disassemble and clean it..


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 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.


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.


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.


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.


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 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' 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.





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.


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..


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.


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.


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 13, 01....... Rev #3..............

Re: General Moped Troubleshooting and Tune-Up Guid

gimmiejimmie /

Fred, I need more info, please be more specific....What kind of cereal? :)

Re: General Moped Troubleshooting and Tune-Up Guid

Ron Brown /

Got to be Frosted Flakes!

Honey Bunch 'O' Nuts !!!

Not really... I think it was Raisin Bran... generic brand from Meijers

lessee... the Girl Scout cookies were Thin Mints.

The mac and cheese was Meijers store brand also.

The extra .002 or .003 will advance the ignition timing a bit.

Which as you know from reading here will make yer ped break the sound barrier.

....... ;) .......

2 inches of fresh snow here :(

Grape Nuts !!!

gimmejimmie /

Ten-four on the Raisin Bran, or is that Racing Bran? Stay away from the Grape Nuts, it sounds like a social disease, so does Moby Dick.

Re: General Moped Troubleshooting and Tune-Up Guid

My moped (Kinetic Magnum) calls for a 50-1 ratio of oil/gas. How much is that? Also, can anyone recommend a good brand of oil?


Re: General Moped Troubleshooting and Tune-Up Guid

Ron Brown /


Any name brand 2 cycle oil for air cooled engines will work, the mixing instructions will be on the container for 50:1.

Pre-mix in a gas can so you can mix a convenient amount (like exactly a gallon).

Use an accurate measure for the oil and never use too little. A little too much oil will do no harm.

I use Castrol if that helps.


oil/gas ratio

I'm pretty sure 50:1 ratio means 2.6-2.8 ounces of two-stroke oil per 1 gallon of gasoline. That's what I use. Most of the Moped Army uses something close to that ratio (some prefer closer to 2.8 and some lower to 2.6).

If you can find it, I found little tiny bottles of two-stroke oil in exactly 2.6 ounces. I found it in the lawnmower section of Meijer (a supermarket chain in Michigan). I kept the little container and use it to measure 2.6+ ounces each time I fill up. It sure beats trying to measure w/ something else, since it's exactly the ration you need for a gallon.

I have a 2-1/4 gallon gas can and I just dump two measures of the oil and then put in just under 2 gallons of gas. Swish it around a few times, then fill up your tank. Then ... off you go!


Re: oil/gas ratio


I see you posted 3 to 4 oz of two-stroke oil in your troubleshooting guide. Is that correct? Everyone I know uses 2.6 to 2.8 oz per gallon. Are we running too lean? No one here seems to have any problems at that ratio. Why do you recommend so much oil?

Don't worry.

I do it for safety... a little more oil will protect a little better.

And 43 to 1 is pretty close to 50 to 1 anyway.

It is also just real easy to measure 3 ounces... or 4... instead of a fraction of an ounce.

And remember a whole lot of peds came with the recomendations of 20 to 1.

Plus I have bout 5 different 2 strokes that I have to pre-mix for... 1 moped, a couple of dirtbikes, weedwacker, chain saw... so I pick the one that needs protection the most... and mix one can based on that and don't worry about it.

(I usually run my YZ250 at the 32 to 1)

Don't worry, if you are buying oil that says "for 2 cycle" and you mix at 50 to 1, I think you will be fine...

This is especially true if you buy the more expensive synthetic.

But I buy the cheaper mineral based oil... and I can't be bothered with worrying about 4 tenths of an ounce.

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