Friday, 20 April 2012

aprilia RS 125 will not start and common problems RS125

aprilia RS 125 will not start and  common problems RS125

 Click here see Aprilia RS 125 for sale on Ebay UK

Aprilia RS 125 parts for sale on Ebay UK

I have owned many Aprilia RS 125 bought , sold and owned them .

this is not a comprehensive problems list but the most common problems i have come across.

Fails to start after parking up for a few days/weeks


Problem usually blocked jets , the jets inside the carb are very small and can clog up  after log periods of parking up. this is why Aprilia have fitted a fuel on and off tap , if you park it up for longer than a couple of day id advise to turn fuel off and let bike run out of fuel .

otherwise you may have to take carb off and clean out the carb and its jets out thoroughly , for longer periods or trying
ti get a bike you do not know about use NEW fresh fuel and a New spark plug lost count of how many bikes i worked on till being
stumped put new fuel in a new spark plug cleaned carb and off it went , but being tight and trying to save the few quid for
the fuel and spark plug cost me an hour of frustration .


electrical problems
low battery , faulty battery. these batteries are fairly poor and if left for long periods without riding can go flat and fail to recharge again needing replacement i used to keep old battery but always found when i come to use them they were completely dead beyond reviving do not know why this is must be some scientific reason for it but i have no idea. Try to run the bike regular or remove battery for trickle charging for periods of long parking or replace battery if you just bought bike and struggling with power.

Another problem can be faulty contacts in the wiring loom (block connectors) i always slit these put an electrical contact cleaner in them to ensure good contacts throughout the whole loom.

id do this yearly as rain , moisture can affect these joints causing a white powdery stuff to form again no idea what this stuff is.

if the bike fails the turn over but clicks and you battery is well charged , this is likely to be the relay situated near the radiator this is a device to turn the low current circuit of the starter switch into the higher current circuit of the starter motor but they are shit 

i hate relays tbh they seem to cause more problems than enough especially on modern cars .

basically this about it ive always found if you buy an old rs125 as long as the compression is good (ie piston rings good)

if you clean out the carb and jets ,replace old fuel with new fresh fuel , fully charge the  battery or replace , make sure all electrical connectors are cleaned and fitted nicely add a new spark plug then there should be no problem firing up .


Aprilia rs125 not starting ,

RS125 Non-Starter Checklist

-       NO FUEL please check and put a few quid in any way especially rs125s i have ran them out loads of time even though i see

a bit it the tank , pushing bike to garages cured me of this i never use reserve if possible.

If there is a nick in a tube or you have a leaky carburettor, your fuel could have escaped and evaporated over the course of a few hours (Lift your filler cap and check that there is fuel visible in your tank and above reserve).

Turn the engine over and make sure that a good volume of air is coming out of the exhaust ie no blockages to air inlet or exhaust system.

Make sure the choke is not flooding the engine

Either remove the spark plug or take a good plug that you are certain works (ive known brand new plugs fail causing havoc and hours of messing about before i tried another new one and bike started !!)

, and connect it to the HT cap , Touch the end of the plug to the frame via the insulated cap or using insulated pliers beware of getting a shock .

Hit the starter button and look for a spark.

Check the original plug in the same way to make sure that it isn’t the source of the problem.

Make sure that the HT lead is on plug.

Make sure that everything is plugged into the CDI as it should be.

if you getting this far see below 


You need all of the above to get the engine to run.

Remove the plug, reconnect it to the HT lead, hold it on the cylinder whilst turning the engine over and you should see a spark.

Whilst plug is out do a compression test. use a decent compression gauge to do the test .

good compression is a must <90psi and bike would not start <100psi starting problems risk of siezure 120/130> good ,

Check fuel is fresh and getting to the carb.

Check air filter is clean.

check timing spark problem - duff plug, cap, ht lead, coil - CDI , check timing .

Try the obvious first.


You think "Ive got fuel" Its always worth actually lifting the filler cap to visually check for fuel. Many people have had £5 of fuel leak out through a nick in a tube or due to a poor carb and this will evaporate over the course of a night, its happened to me a lot on rs125s even though you can see a bit of fuel in take enough for a quick spin next thing you know your pushing bike back

if you can see a bit of fuel in bottom of tank you aint got enough in fill at least half way to eliminate it . 

Kill Switch - Check It Now. We've all done it before left it off, or had someone else fiddle with it unbeknown to you when you get in a panic it can easily be missed and its shit if you take your take off 

or even fairing just to find its the kill switch off !!.

Check The Exhaust for blockages. A friend of mine took his scooter back to the dealership. where they claimed to strip the engine down, before noticing a bottle cap on the exhaust.

If your still not firing by now, you are almost certainly going to need to buy one thing at least before you are. However don't forget to give the bike plenty of chance to fire up. Don't just give the button a little second long tap and expect magic all the time. Check the choke position too.

Now I would say you need to start testing for a spark.

Get Yourself to a point where you can remove both the plug top and the plug from the engine. If like me you have numerous plugs laying about (AND YOU KNOW FOR CERTAIN THAT THEY ARE INTACT) it is often quicker to put one of them in, instead of taking yours out. Whip the plug top off and put the replacement plug into it. Now you must Earth the plug using either the threads or the electrode at the very bottom of the threads. You must get the plug somewhere so you can clearly see if it sparks, and yet it has a perfect contact with the Earth of the bike. I have yet to own a bike with all engine paint still intact so I usually just put the plug on the engine. You could use the frame, or better still battery negative - you're guaranteed an Earth there.

Don't forget the kill switch and ignition switch. You will get a jolt off a plug if you hold it so the spark can get you. if your brave Hold the bakalight at the top, or the plug top or use a hammer as i do to hold plug to earth (frame/engine etc).
Is it sparking?

If yes, (and you aren't already using the original plug from the engine) take the original plug out and check that one. If it doesn't spark now, buy a new plug.

If no spark, (and you are using the original plug) buy a new plug.

If no spark, (and you are using a plug you know is good) you have problems.

Check all the wires are plugged into the Cdi unit. Inspect these wires for chaffing they may have been cut right through from chaffing on something else. Check the HT lead (the fat wire the spark plug top is on) is screwed into the coil tightly and that the plug top is screwed into the HT lead tightly.

if still no spark you need to get WSM out and start test alternator and regulator form correct operation (ill do these tests someday as posts )

just one thing to add.

The starter relay is located just behind the radiator. It is positioned so that the all the wires connect upwards into the unit. This means that it is possible for one (or more) of them to fall out. The symptom is that the starter will not turn the bike over at all but you can bump start it.( If you don't know how to bump start a bike I might do a 'how to' on that if there is any interest) If the wires are all as they should be the relay gets to be suspect. Like all other electrical components , they don't last forever.

Worth knowing I reckon, Oh and don't forget the fuses !

i just done a new post of Spark diagnostics here Aprilia RS 125 No spark - Not sparking troubleshooting


if you have a problem ask in comments below and this section may help others .

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