Aprilia RS 125 died

[DEADmetal]

Hello guys. I was riding my RS 125 the other day, lane filtering at the intersection at very slow speed (revs at idle range), no accelerator and it made a weird high pitch sound, as if there would be a tiny explosion somewhere, then after a second or two it repeated and the engine died (perhaps it was backfire, i'm not sure).

Tried to restart it with choke on and off, tried to bump start it. It just randomly gave a backfire (just the sound) but it seemed as if premix doesn't ignite at all in the cylinder.

Changed spark plug - same result. What could have happened? What has probably happened?

Thanks in advance.

[Just_James]

From what you've described I'd suspect the woodruff key has given up.

My first port of call would be to remove the flywheel and check that first.
____________________
Current Bikes / Projects: 1999 Rieju RS1 50
Previous bikes - 1986 DT125R (field bike), 1989 KX250, 1980 KX420 (with 500cc big bore), 1992 YZ250, 1988 KX500, 1989 XR250R, 1988 VFR400R NC24, 1999 Cagiva Mito 125, 2008 Rieju RS2 50 , 1993 Honda NSR 125

[DEADmetal]

[P.addy]

It's an RS. When was it last rebuilt. How long has it sat around for. Why is it premix.

[DEADmetal]

[MCN.]

Why is it premix?

[MCN]

[P.addy]

Unsure why mcn is big derp. It's a 2 stroke. Needs to be ragged.

[MCN.]

[Nobby the Bastard]

[andy_uk]

[MCN]

[Nobby the Bastard]

[DEADmetal]

[Just_James]

If you have access to a compression tester, do it, it takes seconds and isn't going to do any harm.
It won't necessarily rule anything out but could give you an idea of where the problem may be.

Generally though, a backfire issue would point more toward a timing issue rather than lack of compression which is why I'd suspect woodruff key based on what you've said
____________________
Current Bikes / Projects: 1999 Rieju RS1 50
Previous bikes - 1986 DT125R (field bike), 1989 KX250, 1980 KX420 (with 500cc big bore), 1992 YZ250, 1988 KX500, 1989 XR250R, 1988 VFR400R NC24, 1999 Cagiva Mito 125, 2008 Rieju RS2 50 , 1993 Honda NSR 125

[bypass2]

Did you check the new plug was sparking or did you put it straight in. as said check the flywheel/woodruff key first. what about to much 2 stroke oil in the pre mix

[Major Doss]

TBH if something has popped, you will hope it's not due to a loosely re- assembled flywheel/woodruff. The keyway in the crankshaft can wear away to an extent where the critical ignition timing goes to pot/gives up.
Motor strip, best of luck welding/ cutting the keyway..
SEP? Somebody similar who is local to you?

More info req.

[DEADmetal]

Sorry, i was busy so i didn't update the post and made any progress with the bike. The new spark plug is working - blue spark with each stroke when using starter motor (there was also some premix on the spark plug). It's BR9EG and the bike is supposedly derestricted.

I don't know why it's premix, the previous owner said that he was adviced to disconnect the oil pump and run it on premix. I didn't care much because as i said, the bike is for the end of the season.

I used Motul 800 2T (with the road racing bike on the bottle) at 1:28 and it ran "fine".

Now i'm going to look at the flywheel either today or tomorrow and i have some questions about it. Very intense take offs from the lights that day are indeed suggesting that the flywheel slipped (and the key broke) but the bike ran as usual, for like another 20 kilometers after that, with multiple starts. It never bogged down, misfired or failed to start.

I was thinking about it and i can't get it to work in my head. If the flywheel key snapped, why was it still running and starting fine (cold and warm)? Why did it die just after 20 kilometers, while on idle RPM and clutch in, while lane filtering at like 5 km/h?

And another question, must i take the flywheel off to see if the key is in tact or is there a way to make sure with it in place? There should be markings on the flywheel and the shaft?

Major Doss, can you rephrase that question, mate?

[skatefreak]

If its anything like the NSR, you will either need a flywheel puller to get the flywheel off of some wood and bash the flywheel with some wood from behind (the starter hole is well placed for this), gently of course!

In my mind, if you broke the woodruff key it would have shown signs from the moment it happened...
I cannot imagine an event violent enough to break the key without disrupting the ignition timing/flywheel slipping let alone for it to then slip later on in low-loading conditions, it just doesn't 'sit right'.

All of that being said though, it certainly is something that is easy to check and if you are careful and don't wreck the seal it costs nothing so it would definitely be high on the 'first things to check' list

[Major Doss]

Yes, old chap, I can! More information required, which you have furnished, somewhat.

In your OP, you describe high pitched screetches, yet explosions?
I figure the screetches to be flywheel spin; the explosions to misfire resultant of excessive timing maladjustment due to flywheel misalignment due to kersploded woodruff key with possible associated relevant keyway damage. If that makes any sense, can I write for Haynes?

Oh, edit. If you do not have a puller, pls do not hit a crankshaft with anything unless a penod is inbetween the hitter/hittee.

[Major Doss]

SEP- Service Exchange Parts? Kegworth? Northants? Sorry, I have never used them, but they do come highly recommended.
I always purchased pistons, rebores with trusted local engineers (i don't trust the mail/courier system) and did cranks myself, albeit only Vespas/Lammy's and Suzuki GT250's.