ESE's works engine tuner

[Hoebra]

thanks alot, sounds very logic, I will start playing around with it and the Mik Powerjet I actually have becaus its still unused and not worn out, if the results look promising I can go looking for such a Fiat Solenoid or maybe Frits knows exactly wich typ they are from.

[Frits Overmars]

Not the answer you want to hear, but the Mikuni solenoid PJ does not take kindly to PWM at all. The tip wears , due to the constant hammering it gets from being cycled at 10Hz or so, and a " step " appears on the tapered end very quickly.
The Aprilia used a different solenoid for PWM, taken from a Fiat carburetor, that was originally an idle air control valve of some sort I believe ( and way cheaper as well ).

Yeah, well, sort of. The first programmable Aprilia power jet was not a solenoid at all but a threaded needle, the same kind that you'll find as an air screw in most carbs. This needle was screwed in or out by a stepper motor that was originally designated to regulate the idle rpm of some Fiat car engine. It was soon replaced by a real solenoid that was easier to control and could also withstand the 13 Hz pulse width modulation. Imagine how Dellorto felt when their precious RSA carburettor was fitted with a solenoid from Honda-daughter Keihin.....
The pics below show the priceless RSA125 carb and the not quite so expensive Dellortos on its big brother, the rare RSA250.

Anyway the PJ sizing depends upon the fuel used, for race or leaded gas where the overall jetting is run very lean ( simply because it can ) then the PJ size has to be quite small. Using the Mikuni powerjets, this is in the range of 32 to 38 so that the amount of fuel being reduced is small, as the peak power EGT is already hot - well over 1200*C.
Unleaded or pump gas settings that are usually run richer with less compression and more advance, need approx twice the PJ size , up around 70 to 80.
This leans off the mixture alot more over the pipe, as its already inherently much richer. These sizes are independent of the main used, and they work, even in a Lectron with no actual main jet at all.
As for the hard switch point, a good place to start is around 2/3 rpm between peak torque and peak power.
The fuel curve needs to start leaning of at this point due to the fact Scavenging and Trapping Efficiency start dropping immediately past peak torque, even though the Delivery Ratio is still increasing. But this effect is ameliorated alot by pulling out advance as the rpm rises, thus increasing the wave speed in the pipe.
Using PWM, the 0% point is closer to peak torque, and ramps to 100% ( ie no fuel ) somewhere again around 2/3 the way to peak power rpm.
Maybe Frits could confirm this, as I have never actually seen the RSW/RSA PWM table.

I haven't seen those mappings either in quite a while; they must be hiding somewhere in the mass of papers here. They form a multidimensional map with rpm, throttle position, gear selection an deto signal inputs, and ignition, power valve and power jet outputs
What I can do, is give you the settings of the very RSA that unleashed those 54 horses on the dyno, if you promise not to tell anyone.
You must have some Italian by now Wob, so I will leave you to it .


l=========================================
DRVE4734.PC:
2006-10-30; Gilera DRD 071030, LD 120, squish .74,
tubo G10/07 Sam.n°2.BN, tail 23, collettore 36, silenziatore 25,
Denso 34, accensione Poker, carb 42, AU286T2P264Max192m53-4f-P120, benzina Agip +4% Elf 909, disco 152.5°/90°.
=========================================
On second thought, this Italian was quite idiomatic so you could probably do with some clues: main jet 264, power jet 120.

[wobbly]

Thanks Frits, I had seen those small cylindrical PJ solenoids before but never made the connection to Keihin, I just looked at a carb here and yes they are identical to those
fitted to Keihin SPJ off an RS125 or RS250 Honda as of 1998.

Mikuni, in a tune up paper I have for the solenoid kits they sold, say to use a PJ/Main combination of 25/75% - thats not far off the Dellorto combination quoted.
Dellorto mains, you would think, represent mm diameter, but the dont.
For example I have a full range of pinned jets from 125 out to 195 ( 125,126,127,128 etc ) - every one of them
is very near 0.1mm different that the stamped number. ie a 150 pins at 1.6mm.
There QC is atrocious , a 150 can pin at anything from 1.58 to 1.62, and mine were all double confirmed in a diesel injector flow machine.

Super surprised to see the valve open time at 152.5*, way more than other sources have quoted at 140* thereabouts.
I will have to test that once Neels has removed every last strand of hair fighting with the coding.

[Frits Overmars]

Thanks Frits......Super surprised to see the valve open time at 152.5*, way more than other sources have quoted at 140* thereabouts.

Opening an inlet disk at about 140° before TDC is generally considered a practical value. At that point, a slight depression begins to develop in the crankcase, to which the carburettor responds favourably, i.e. changes in the carburettor settings directly result in changes in engine behaviour. And that's very nice when you are adjusting your settings.
However, that slight depression in the crankcase is going to slow down the transfer flow. And if you want to squeeze every last bit of power out of an engine, you don't want anything to hinder that transfer flow.
At low revs, the crankcase pressure has had more time to drop, so you could open the disk even earlier, in some cases even before BDC. But to be able to use that in practice, you need Neil Hintz's wonderful disk valve inlet system with its variable opening and closing points.
Of course Neil, having his Transfer Port Injection, doesn't need to fiddle with any carburettor settings anyway. That man is brilliant. But you are right about his ugly knees, Wob .

[husaberg]

Far more common than Honda RS parts the Kawasaki KX125 and 250 and likely other bikes ran the Solenoid PJ at arround 1999 it'd the "shortie version" as well like a RS body. they also have built in TPS The 125 is the 36mm the 250 has the 38mm.
Wob has detailed how to mod the outlet on the PJ before.

the solenoid is still available $78USD

https://www.cmsnl.com/kawasaki-kx125...oid_211881005/

[jonny quest]

Far more common than Honda RS parts the Kawasaki KX125 and 250 and likely other bikes ran the Solenoid PJ at arround 1999 it'd the "shortie version" as well like a RS body. they also have built in TPS The 125 is the 36mm the 250 has the 38mm.
Wob has detailed how to mod the outlet on the PJ before.

The Yamaha YZ250 has had it continuously since around 2021, YZ125 now has it too, since '24 I believe.

[jonny quest]

Forgot to mention, Kawasaki is coming out with a new line of big bike 2 stroke motocross bikes again. '27 models is the rumor. No other information.

There is a ad for them I believe you can find on YouTube

[F5 Dave]

I spent 1/2 my life trying to extract as much power out of 50 and 100cc commuting bikes. Or original rules were purposefully quite restricted and the bikes didn't evolve much past 1970..

Anyway the 300cc 'big bore' (but not really) dirtbikes I ride now are fantastic for other reasons.

If your body will allow it, please buy one and enjoy a ripping 2 stroke while they still exist. We all get old. Do it if you still can.

[TZ350]

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Attachment 356395 Attachment 356394 170/88 ... Red Line on graph.

70cc. The crazy inlet timing started easy enough and made more power and even idled but I did not put any effort into trying to tune it. Flagged it for something more traditional timing wise.