aprilia rs50cc moped problem

[normspanners]

Has anybody had any experience of these little beasts my nephew has one,he bought it but would not start off the key, it would crank fine but would not fire all you needed to do was walk it 3mtrs and drop the clutch and it was away, hot or cold. It has had a new piston and pot btw by the previous owner I had a quick look and IMO there was no real spark you could just see it in the dark, so a new stator was ordered and fitted with no difference BTW there is no adjustment for the stator it just fits .
During fitment of the stator it was noticed the mains where VERY worn, so engine stripped and new mains and seals to keep the flywheel in closer tolerance to the stator . Made No diff.
So new CDI ordered and fitted, still not good will start off the key sometimes but there is still in my view a VERY weak spark, and the engine bogs out easily, BUT then when it goes IT GOES it picks up and flies!! we have tried removing the oil pump blanking the input to the crankcase and running on premix. Crankcase has been smoke tested, it has a 95 main jet when 80 is standard but still looks slightly weak mixture, I managed to get it to run better, in desperation by putting several layers of denim over the air filter. PS reed is good and carb been cleaned twice. It has an arrow after market expansion exhaust btw.
ANYBODY?

 

[octo0072000]

sounds like the starter is pulling all the power away from the spark will it start if you put jump leads on it from a good battery
i presume no kick start no air leaks on inlet side

 

[66-V8]

New spark plug?

 

[DanielW]

Is it an auto choke on the carb? if so there is a resistor linked to auto choke and bike frame,replace this with a wattage value slighty higher than specified on resistor body but keep the resistance the same.

Find a metal clad type resistor.

 

[DanielW]

What do you mean drop the clutch? as far I know most mopeds these days are automatic clutch,that is when you start the bike the brakes are pulled in and as soon as you release the brakes the bike pulls away.

 

[octo0072000]

aprilia RS50 is more bike than moped

 

[DanielW]

Laughs,your right,I was thinking the SR50 not the RS50....anyway if its auto choke? then the resistor problem still stands but not 100% on it being that.

the fact the bike starts says its not the ignition system

 

[normspanners]

Thanks for the replies guys but

sounds like the starter is pulling all the power away from the spark

Starter has nothing to do with ign totally separate, but is a new battery fully charged.
not choke as said same hot or cold. ps manual choke it can adjust running by playing with the choke hence trying the restricted inlet which did work sort of. Also if weak spark less air doesnt blow the spark out as easy.

New spark plug?

Tried even softer one

the fact the bike starts says its not the ignition system

But it doesnt start, all the time and when it does it runs like s**t
as said the spark is not good IMO

 

[DanielW]

http://www.scooternations.com/

 

[MCKDAVID]

"Starter has nothing to do with ign totally separate, but is a new battery fully charged."

doesn't rule it out completely. It could still be a volts issue, if the starter was pulling the volts down, the coil wouldn't be getting a full 12V which could result in weak spark. Mind you if you're still not getting it running right when it does run, it would probably rule that starter volts drop out.

either way I'm confused, your first mail said it flies when it runs, now your saying it runs like ****. What's changed, did the new CDI make any difference?

Two strokes are finicky beasts at the best of times, sometimes you've got to go back to basics and check it all.

could start with a few of these.
- clearance between rotor and stator
- resistance of cdi (even if it is new)
- dodgy coil / HT lead / plug cap
- electrical connections between them
- Oil / fuel mixture oiling plug
- have you checked all the earths?

That all said, sounds like fueling to me, especially if it's running ***** and had an after market pipe and uprated jet put on.

Their pretty basic machines at the end of the day, stick at it you'll get it

 

[normspanners]

Thanks BUT

doesn't rule it out completely. It could still be a volts issue, if the starter was pulling the volts down, the coil wouldn't be getting a full 12V which could result in weak spark. Mind you if you're still not getting it running right when it does run, it would probably rule that starter volts drop out.

It is totally separate, it will start without a battery!

your first mail said it flies when it runs

BUT then when it goes IT GOES it picks up and flies!!

What i meant was, it bogs out, BUT then when IT decides to go, it flies, generally on a slight downhill, show it a slight uphill and thats it, it loses power till it cuts out. which makes me think the exhaust cant be blocked. I can blow large amount of air through it no problem.
- clearance between rotor and stator----- as stated cant be adjusted but new mains
- resistance of cdi (even if it is new)------ exactly same both check out fine with meter
- dodgy coil / HT lead / plug cap -------- coil combined CDI new lead
- electrical connections between them----- new
- Oil / fuel mixture oiling plug --------- plug looks weak ish when it flies and do a plug chop. looks good at idle
- have you checked all the earths? ------- all seem fine
I many years ago,in my teens, used to spanner for racing twostrokes and now build comp cars, so have a fair idea on the principle.
what concerns me is this apparently very weak spark.
All my bikes have a fat blue spark, that can be seen in daylight.

 

[lazybones51]

Have you checked the compression? I had a Cagiva Mito 125 (Highly strung Italian 2 stroke), was a pig to start and didn't idle well but once it got going it flew. Turned out the rings were near enough shot. I know you said it had a recent rebuild by the previous owner, but it's worth checking compression as it could be low.

 

[octo0072000]

flywheel de magnetised

 

[Wendelspanswick]

Have you tried a timing light on it?
That way you can test if you are getting a spark under compression.
Hopefully I am not teaching granny how to suck eggs.

 

[normspanners]

flywheel de magnetised

funny was thinking about that this morning!!
but then thought only way to test was new, but having said that the genny is fine and the lights are VERY good.

Have you tried a timing light on it?
That way you can test if you are getting a spark under compression.
Hopefully I am not teaching granny how to suck eggs.

Again most of my stuff has been nicked but, I found my snapon spare light to take on rally gb and was thinking of giving that a go.trouble is with this little thing it has a side ally frame and you cant see much unless you have the tank up then you cant run it.PS timing coil was new with the stator complete
PS I dont mind my granny sucking eggs we all can forget things

 

[normspanners]

Have you checked the compression?

No I havnt checked it, thanks
the ring/piston looked good and head gaskets ok, no pressure in coolant. and it feels ok on push.
but might give the gauge atry
ps it generally starts on key with a new plug but after its run it generally will only bump even though the plug looks good. and is not wet.

 

[normspanners]

Have just tried my chainsaw coz it was lazy starting (just needed a few pulls) coz old last yr fuel and the spark on that is easily twice the intensity..

 

[Windy Miller]

No I havnt checked it, thanks
the ring/piston looked good and head gaskets ok, no pressure in coolant. and it feels ok on push.
but might give the gauge atry
ps it generally starts on key with a new plug but after its run it generally will only bump even though the plug looks good. and is not wet.

What is the gap on the plug?

I had a similar thing on my old step thu Garelli when I was a boy. With a new plug it was fine. After running a few miles it was hopeless. Book said 25 thou plug gap, but a bike mechanic said try 18 thou. Ran as sweet as a nut for ages after that!

 

[MCKDAVID]

I know you said it can start without the battery, but I was wondering is it a type of cdi that needs an external voltage to it to "excite" the secondary side to increase the ouput power? any external power supplies to it?

 

[DanielW]

I know you said it can start without the battery, but I was wondering is it a type of cdi that needs an external voltage to it to "excite" the secondary side to increase the ouput power? any external power supplies to it?

The CDi gets its voltage from rectifier and the genny on the stator supplies that voltage to the rectifier,I think the battery is only for the lights,horn and indicators,starter motor?