[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked)

Frits Overmars a écrit:

Regarding the Aprilia RSW/RSA125 single, Jan Thiel told me that in seven years of testing the racing department had not been able to establish which was best: low or high inertia.

But knowing there is a Fiat Uno part on the Aprilia 250 makes me a little be disillusioned...

Try to look at it from the positive side, Marc. You could buy a Fiat Uno and feel very happy .

I don't know about that Frits, sometimes the humble two stroke makes me feel positively silly


Is the stepper motor controlling fuel on what looks to be the power jet circuit ???

Is the VHSD a good carburetor to work with?


Je ne sais pas à ce sujet Frits, parfois l'humble 2t motor, rend me positivement stupide



C'est le moteur de pas contrôler carburant sur ce qui semble être la puissance jet circuit ???

I am off to look for Fiat stepper motors :)

[Vous devez être inscrit et connecté pour voir cette image]

This is very similar to the solenoid that controls the power jet on the 125 Honda rs?
In this case it is not a stepper motor but a solenoid operated on/off.

Here the solenoid used on the Honda:

[Vous devez être inscrit et connecté pour voir cette image]

Institute of TwoStrokes a écrit:

Is the stepper motor controlling fuel on what looks to be the power jet circuit ?

Yes, it moves a threaded needle in the power jet circuit.

ridley a écrit:

This is very similar to the solenoid that controls the power jet on the 125 Honda rs? In this case it is not a stepper motor but a solenoid operated on/off.

Yes Ridley, it is very similar. In fact it is identical! Jan Thiel just informed me that the Fiat stepper motor is no longer used. It has been replaced by a modulating valve that opens and closes with a 15 Hz frequency. The valve, fitted to Aprilia's Dellortos, is produced by... Keihin!

Hi guys,
I still have not much time though, but I managed however to build a new valve, and I did prepare a 70cc cvt engine.I will do some test with it this weekend.here some pics of the new valve. 8)
[Vous devez être inscrit et connecté pour voir cette image]

It looks good, Michael. I can't wait to see the test results .

Thanks,
and me too,I want to test it as soon as possible.

Hi Michael and Frits, do you not think it would be better to leave the reed section in its normal position and open another passage, maybe helping to stop reed damage.

Hello Fritz and thank you for your reply. Kehin on an Aprilia, it may be that globalisation

Fritz, what do you think of the idea of using a power jet (with an electronic management) downstream of the carburetor, this in order to enrich the mixture slightly in the case of detonation (like on the 500-Muz Swissauto)?

Je veux bien être l'affreux qui fracasse les cranes de ceux qui parlent mal le Français, mais là, si quelqu'un pouvait traduire même en survolant, j'aimerais comprendre aussi...

ce que je comprendé olé, c'est que Ridley y demande à Frits si le signal d'un capteur de déto ne pourrai pas aussi servir d'information à un boitier de gestion électronique qui déclencherai un gicleur de pointe (PJ vue plus haut) en séquence de déto histoire de calmer la désintégration de son piston.

Exact Manu, mais en aval du carbu. Mickie, traduction possible si toi donner tél de la copine gros poumons

pfpraider a écrit:

Hi Michael and Frits, do you not think it would be better to leave the reed section in its normal position and open another passage, maybe helping to stop reed damage.

The main passage should be as straight as possible. And if we would add a T-junction for a separate reed passage, we would need some sort of valve in the main passage anyway.
Reed damage should not be a problem. In Michael's new version not only the reed but also its bedplate is hinged, so the reed has a better support now. And we can use a stiff reed that would cost a lot of power in a normal reed valve engine.

ridley a écrit:

Frits, what do you think of the idea of using a power jet (with an electronic management) downstream of the carburetor, this in order to enrich the mixture slightly in the case of detonation (like on the 500-Muz Swissauto)?

Detonation-suppression is already being used. But why downstream? that would give the fuel less time to mix with the air.

mickie a écrit:

Je veux bien être l'affreux qui fracasse les cranes de ceux qui parlent mal le Français, mais là, si quelqu'un pouvait traduire même en survolant, j'aimerais comprendre aussi

I have tried translating with Google but the result is so bad that even I can see it's not correct french. So to avoid misunderstandings I use english, but I confess I feel somewhat embarrassed about using a foreign language in your great forum.

ridley a écrit:

Mickie, traduction possible si toi donner tél de la copine gros poumons.

Mickie, what is the french word for blackmail 8) ?

Frits Overmars a écrit:

ridley a écrit:

This is very similar to the solenoid that controls the power jet on the 125 Honda rs? In this case it is not a stepper motor but a solenoid operated on/off.

Yes Ridley, it is very similar. In fact it is identical! Jan Thiel just informed me that the Fiat stepper motor is no longer used. It has been replaced by a modulating valve that opens and closes with a 15 Hz frequency. The valve, fitted to Aprilia's Dellortos, is produced by... Keihin!

Hi Frits
is it needs to put a specific program in the s-das2 to manage this new power jet
best regards

I could not say. I suppose it will depend on your version. And I understand that private users do not have the same programming facilities as the Aprilia-supported team mechanics, but that is outside my field.

Frits I have been thinking about plugging the ends of piston pins, like the scary priced Aprilia pins. The Aprilia pins look like they a plugged with aluminium(???) I was going to try some sort of epoxy coated balsa(yes I am that cheap), will that hold up to the temperature(200 deg C). I know the reason is the short circuit between the transfers and the auxliary exhaust port.


Frits j'ai été penser à brancher les extrémités du piston pins, comme la effrayant prix Aprilia broches. La Aprilia pins ressemble qu'ils un branché à l'aluminium(???) j'allais essayer un genre de époxy balsa(oui, je suis bon marché), sera que contenir jusqu'à la température(200 deg C)

Je sais que la raison en est le court-circuit entre les transferts et la auxliary port d'échappement.

The Aprilia piston pins have welded-on steel caps. They are made by Pankl (A) which of course is the most expensive address around (the best F1-conrods come from Pankl).

I recognize your line of thought regarding epoxy-coated balsa; my first plugs were made out of polyurethane foam.
I also tried teflon; it was no way near heat-resistant enough. Nowadays I use some space-age material of which I am not going to give you the name; it is horribly expensive and finding out the optimum material has also cost me an arm and a leg (I developed them for my FOS scavenging system where the overlap between transfer and exhaust ports is far larger than in a conventional cylinder).

Avoiding short-circuiting between transfer and exhaust ports is the most obvious goal of the plugs. But it is not the only one. Do you remember Honda's TRAC system where at low revs a resonator volume was coupled to the exhaust duct to lower the exhaust system's Helmholtz frequency (Suzuki and Kawasaki used similar systems)?
The volume inside a piston pin does more or less the same: during every revolution it is momentarily connected to the auxiliary exhaust ducts and it dampens the system's resonance, even if you don't want it to, i.e. when the engine is running in the power band.

Below left you see the latest version of the original Aprilia piston pin with domed end caps at 136 euro a piece, and at the right my re-usable click-on plugs (that also make the usual steel-wire clips superfluous) at a fraction of the price

[Vous devez être inscrit et connecté pour voir cette image]

If you have them in 16,15 and 14mm I'll buy them off you.

Yes I remember the TRAC, KIPS, AEC even KTM had them on a 380 (why more bottom end on that ??? ) I have a similar chamber under construction powered by Ignitech/Zeeltronic, so simple and effective when you are forced to race with 4T 'handbrakes'

GAS GAS 300 has one to but with X10 less parts than KIPS.

Institute of TwoStrokes a écrit:

If you have them in 16,15 and 14mm I'll buy them off you.

I've got them in 15 and 12 mm (I wondered why you were asking for 16-and-a-bit mm until I realised that you must be using Church of England-notation; I saw the comma as a decimal indicator 8)).

Bonjour,
J'ai quelques photos sur le montage et le calage du distributeur rotatif RSA? (voir avec marc l'admin) si c'est possible.
[Vous devez être inscrit et connecté pour voir cette image]

Bien sûr que c'est possible.

Pour les afficionados et les autres Voici le sujet qui fait couler l'encre: mais comment ont-ils fait, quel est le secret ou je ne sais encore bref vous allez tous savoir sur le montage de l'arbre du distributeur rotatif du moteur RSA 125 APRILIA/DERBI l'avion de chasse europeen face à l'envahisseur nipon. Pour confirmer le sujet sur la qualité des aciers utilisés en france il y a une entreprise en bretagne qui est spécialisée dans la fabrication des pièces moteur pour les F1 (le sujet parle de l'acier qui est utilisé pour la bielle en autre).