Aprilia RS125, strange mechanical problem, help!

peterlaurens · L Plate Warrior Joined: 14 Apr 2004 Karma :

Hi,

I have a 2000 model Aprilia RS 125, it's been garaged all its life and ridden properly - in short, it's in great nick - I bought it second hand as my first bike and have had a lot of fun out of it... it has however started giving trouble as follows...

I start the bike up fine, and take it for a spin, performance is great as always, after a few hundred metres the bike begins to warm up a bit, but then (always under 1km of riding) the bike seems to just stop! It always seems to be as I am accelerating, the thing starts to pull just fine... then... the engine stops and I am free-wheeling, as if the spark plug just stopped working. This is so weird, as I can be revving through 6 thou, 7 thou, 8 thou really nicely, then the engine stops and I free-wheel to a stop!

What happens next is perhaps most interesting... the bike refuses to restart, unless I whack the choke on full, then it will start ok. I then ride it like this for about 30 metres before the exact same thing happens again, it konks out. This time, it will not start choke on or off. I must wait 10 - 15 minutes, then it will start fine and this whole loop starts all over again.

Mechanically the bike seems to be fine, I have taken the carburettor apart and it looks fine and moves well. The spark plug is *brand new* (this was the first thing I tried).

Interestingly, I can stick the bike on its stand in my yard and rev the thing to hell (watching the temp of course) and it'll never seem to die. It only seems to be when there is some strain on the engine (ie. it's moving the bike someplace).

Also, this happened last summer, and I seem to remember spraying a load of carb and brake cleaner into the engine through the spark plug hole to try to clean it out... and this seemed to work. I tried that again this time, and no such luck... it continues to konk out as described above.

The weather is warm here about 20 degrees C, but not sweltering, when the bike is running performance is excellent, so it's not as if there's a degradation in performance before it konks out or anything - it just suddenly goes. Also it is *guaranteed* to happen within a kilometre of riding.

Any help any of you may offer is going to be so gratefully received... none of my mechanically minded friends have any idea... I don't have the money to take it to the shop to be looked at, and anyway, with the nature of the problem they may well overlook it, as the thing has to be ridden on the road for a few hundred metres before the problem arises.

Again, any advice much appreciated, I'm pulling my hair out!

Thanks

-Pete

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

What about 2 stroke oil? is the tank topped up?

Its not carb icing or anything like that...

Sounds like the bike is running lean and its overheating or something...

I now pass you to the Superhero of Strokers, Keith. Any ideas? Smile

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Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

peterlaurens · L Plate Warrior Joined: 14 Apr 2004 Karma :

The oil is topped up full with some fully synthetic stuff.

As for carb-icing, I'm not hugely mechanical but I'm guessing you mean sticking of the carb slide? Well, I took a look at that and gave it a shot of WD40 just to be sure and it's going up and down perfectly I think.

Thanks for your quick reply! Any more help much appreciated!

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

I take it you are from the UK?

If its twenty degrees (centigrade) there then its too warm for carb icing. Carb icing is where water vapour freezes within the carb and effectively changes the shape of the venturi so that fuel is not drawn from the jet.

This happens because the venturi principle cools the air entering the engine. It usually happens when the ambient temperature is around five degrees centigrade. Thay would produce the exact symptoms you describe, even down to the bike working fine when it isn't moving... when it does cut out the heat from the engine melts the ice and the bike fires up again.

I would imagine that with a mild case of carb icing adding choke would allow you to fire up the engine but then the icing would get worse.

Sound familiar? Smile

if it is 20 degrees like you say then it shouldn't be a problem! Question

____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

peterlaurens · L Plate Warrior Joined: 14 Apr 2004 Karma :

That is interesting, and good to know about... but it's a gorgeous day here and about 20 deg C, the bike hasn't been out overnight (when it was a lot cooler) but in the garage... even then not down to 5 deg C i think...

yeah im in the UK, down in Jersey.

Keith · World Chat Champion Joined: 24 Mar 2004 Karma :

have you thought it might be a daft blockage in the air filter?
it may well not need a lot of air when revving it in the garden, but once you get going and into the powerband it needs much more, hence why it overheats / stops.
i'm rather mechanically illiterate, so just slap me if i'm talking a load of gibberish Wink

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MarJay · But it's British! Joined: 15 Sep 2003 Karma :

Not being funny NS-keith, but you're not the keith who I was referring to in my above post. I'm referring to the artist formerly known as Kickstart! Smile

____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

My best guess would be that the bike is suffering from fuel starvation.

Main causes of this are a blocked fuel filter, kinked fuel hose or a blocked breather hose into the petrol tank.

How old is your RS125? If it is a newish one then they have a 28mm carb (top of the carb is held on with 2 screws). On these the fuel filter is under a banjo shaped cover on the side of the carb. The filter is a gauze disk about the size of a 20p piece. If it is an older bike with the larger 34mm carb then the fuel filter is also on the side of the carb but harder to find. Find where the fuel pipe goes onto the carb. About 1" down from there you will find a bolt. Undo this and you will find the filter which is a gauze tube about 8mm deep and about the same diameter. Remember to turn off the petrol before checking either, otherwise the petrol will go everywhere.

The fuel hose can get kinked. However you can hopefully see this without lifting the fuel tank up.

If the breather hose is blocked then when the engine konks out it should restart and do the same distance again if you remove the petrol cap for a short while and then put the cap back in place. Not sure where the breather is on your RS125.

All the best

Keith
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Keith · World Chat Champion Joined: 24 Mar 2004 Karma :

need2befaster · L Plate Warrior Joined: 14 Apr 2004 Karma :

wot sort of milage is on it....this is only a suggestion but could it be time for a piston and ring change....i had an old vespa 125 did somthing similar, when it got warm it would just stop...expansion and all that jaz...but would sit ticking over just fine...maybe the previous owner wasent just as kind as you..
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peterlaurens · L Plate Warrior Joined: 14 Apr 2004 Karma :

The bike has only done 4,500 kilometres, so I don't think it's anything really serious mechanically.

Keith thanks ever so much for your detailed instructions, they are very very welcome and I will give your suggestions a good go and let you all know how it goes.

Thanks again for all your help... any more suggestions? Keep em coming!

tom_prs · L Plate Warrior Joined: 11 Nov 2005 Karma :

hi .. i have had this problem with mine. mine does exactly what you said when it just cuts out then you have to put the choke on full. mine also revs up by itself to aobut 8/9,000 revs then cuts out. ive been trying to fix it for absoultly ages then gave in and took it to a garage. they said that air is leaking in to the engine somewhere through the carb. or the oil filter. i havent got my bike back yet (its been in for a few days) but when i get it back ill let you know whats the problem.

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

tom_prs · L Plate Warrior Joined: 11 Nov 2005 Karma :

whatever .. i got mine back they basically replaced the whole fuel system and the choke was stuck on (which didnt help). the carb was also totaly mucked up.

Lee_367 · Brolly Dolly Joined: 22 May 2004 Karma :

Any trouble i've had with 2-strokes, the first thing i've done is replace the spark plug and make sure its gapped correctly.

Give that a try.
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