ESE's works engine tuner

[Mollihead]

„Additionally, some two-strokes have a tendency to lean out as they pass beyond full
power rpm with conventional carburettors, but the Powerjet Mikuni is able to cure
this“

Sounds like a contradiction to the statement of Wobbly:

„this overcomes a carburetors natural tendency to go richer and richer past peak power“

And what is the influence of power jet position? PWK is at the top, Mikuni more to the center. A lot of additional variables

[husaberg]

„Additionally, some two-strokes have a tendency to lean out as they pass beyond full
power rpm with conventional carburettors, but the Powerjet Mikuni is able to cure
this“

Sounds like a contradiction to the statement of Wobbly:

„this overcomes a carburetors natural tendency to go richer and richer past peak power“

And what is the influence of power jet position? PWK is at the top, Mikuni more to the center. A lot of additional variables

am not sure what he was meaning but with the old ones if you jetted it for most conditions ibelow absolute max rpm it was never right right at the top end.
if you carb is rather large, they tend to not auto enrichen like a smaller one will past peak power RPM. This was a good safety feature.
pretty sure if you are on an ultra large carb the opposite can happen. I tended to run fat and forgiving.
Wob can answer the position question he used to move the ones on the PWK shorties when using them for non MX bikes
I can't find the post I was looking for.

The carbs of the MX bikes with the Powerjet and TPS all have the air guides in the bellmouth in front of the slide.
This kills a heap of flow compared to an SPJ, but does give good response down low ( worth a couple of Hp on a RS125 in the top end for example ).
The flow thing isnt really an issue for a bucket motor as they are only made in 36 and 38mm - so plenty big enough to get the flow back with area.
The SPJ will handle more downdraft due to the Powerjet fuel pickup point in the bowl.
The MX ones have an issue with this as the suction point is right at the back of the bowl and would not be under water if tipped up too far.
I posted a pic of the fix a while ago.


Are the teflon seals for the RS125 kit, available in a range of sizes ie where do they come from.


You dont want the piston hitting during normal running,just short of a hit is whats needed at the peak rpm you would normally see on track - often when idiot riders bash the shift pedal on the overun into corners,
with no dynamic com pressure at work.


Saw an amazing ride in the weekend.
A 70+ guy now holds the lap record for post classic pre 82 Junior at Pukekohe,on a C model TZ350.
Im sure the toroids made a difference,but even with Dual Carbon pads you have to know how to go down inside 4 bikes at a time into the hairpin.
Poetry in motion on a bike - makes all the hard work seem easy.

The powerjet dump tube on the KX carb is down very low in the venturi,I have been bending this upwards toward the carb centreline.
This is due to the MX bike using the solenoid switching at very low rpm.
In a race situation you dont need vacuum on the jet down low and up higher is where the dump tube is on the SPJ carb from Honda RS125/250.

The problem as I see it with adjusting the AFR trying to simulate a PJ being switched off is that this has two effects on the result.
It will increase the temp seen by the pipe, but I believe also the code does a calculation of the energy available in the fuel, and adjusts the power
that quantity will deliver - maybe in this case the two counteract each other exactly.
This is because max power is seen down at a rich mixture,around 12:1, closer to stoichiometric there is less power available, in theory and reality.


But the other thing you should realise is that although a solenoid powerjet is reducing the fuel delivered to the engine, it
is actually correcting the natural,progressively richening mixture coming from the carb, not reducing the AFR below what is was previously.


I will ask Neels about a workaround, but my reaction would be to use the pipe wall temp/rpm input screen,to increase the average temp in the pipe after a set rpm.
Going from a " normal " 50* wall temp to a 150* wall temp at 12,000 will for sure have the desired effect on the overev.
In reality the temp will increase gradually, so a temp ramp over say 1000rpm would simulate reality better.
I dont know if the code interpolates temp between the set points.

Yea running Avgas correctly means you will be lean at peak power, and using a powerjet a little too big will for sure detonate in the overev as it turns off too much fuel.
If the set point is too low or the jet is too big,you will feel the switch almost like a 7th gear,the bike takes off as the pipe heats suddenly.
With the diameter and rpm set point on the money, it just becomes a seamless increase in rpm ceiling.

We did the reverse of this years ago , having to change from Meth back to petrol ( Avgas ).
On Meth it was at 18:1 compression , no extra advance anywhere , and made 48.5 Hp ( 125 TM - MX engine )
Changing back to AvGas I dropped the com to 15.8 , lengthened the pipe 15mm in the header and 15mm in the mid ( then later built a better pipe ).
Best advance curve again was as it was previously.
This setup made 43 Hp but had nowhere near the mid power , and had lost alot of overev.
I wound in some mid avdance , but this had no effect , and the only way to get the overev back was to fit a solenoid powerjet that stopped the carb
going rich over the top of the pipe.
Obviously the Methanol didnt mind going rich and kept on reving hard.
Lengthening the pipe pulled up the mid , but lost even more overev.
So the final result was a loss of 5 Hp in 48.5 = 10.3% but the real penalty was the powerband width.

In the tests I did years ago having the powerjet discharge end mounted down from the top of the carb bore and later , shortened , gave a smoother and more
gradual flow rate transition much higher up the fuel curve. The Keihin carbs with the discharge nozzle mounted below 1/2 throttle , start to flow almost immediately the slide passes the tube.
Of course later , using a solenoid with PWM drive as Dellorto did , gave electronically the same gradual flow ramp up that didnt suddenly richen the fuel curve in the midrange as soon as the slide was high enough.

Hey Mr Pig , regarding the carb question again , I am tending to the 36mm carb if the rest of the project is dialed into being used for roadracing.
The point here is that using the TPS and the Solenoid allows a longer pipe design , that will then overev easily by switching of some fuel just past peak.
If its as I suspect a WankStriker version , tap out the powerjet tube and machine out the wings in the bellmouth floor.
These work well in an MX scenario for throttle response below the pipe , but have a huge loss of airflow CFM when compared back to back with say a PWM.
You can tune the intake length slightly long to pump up the front side , and one of those sexy looking carbon fiber add on bellmouth extensions would help there as well.

[katinas]

"Dial a jet" old adjustable things from the nineties. Made in USA.

[wobbly]

So Yamaha were completely wrong with the idea of switching ON the PowerJet solenoid - ie switching OFF fuel in the overev, yea right.

[husaberg]

Some light reading to help you through the weekend.
Attachment 355947

3x times past the mainjet.....

its a inside kiwi joke.

So Yamaha were completely wrong with the idea of switching ON the PowerJet solenoid - ie switching OFF fuel in the overev, yea right.

I think we are cross communicating. I think yamaha was just trying to get the mid and upper range correct
my understanding from what you wrote was the solinoid pj's were not about correcting a wrong mixture in as much but putting heat into the pipe to speed up the gas so its effectively making the pipe shorter?
Frits explanation as to why it works on Piston ports makes sense. the other thing to consider is those VM mikunis were very basic, not that much more an an Amal with no high speed airjets. later carbs were much more sophisticated.

[Frits Overmars]

So Yamaha were completely wrong with the idea of switching ON the PowerJet solenoid - ie switching OFF fuel in the overev, yea right.

I added one sentence in that powerjet pdf, hopefully making it more understandable for everybody. You might want to take another look Wob.

[wobbly]

I should add that imho, the hose up to the high point of the PJ was helpfull in that it created a time lag due to the fuel head working against the early suction created
by having the PJ nozzle in the middle of the carb.
Thus as soon as the slide passed 1/2 way up the VM carb bore there was negative pressure acting on the nozzle exit, but the hoses high effective fuel head momentarily slowed down the initial
discharge rate, helping to not dump fuel into the mid range, where its not wanted nor needed.

Of course the easier and better way to do this is to shorten the nozzle length such that nothing happens till the slide is up about 3/4 of its stroke , as Lectron and many
tuners did to the old VM carbs on TZ Yamaha's for years.

My comment about the Yamaha solenoid switching was in response to the quote from someone saying that carbs naturally run lean into the overev, if that were true
then the solenoid would be switched OFF ie turning the fuel ON to help cure this non existent effect.
Your comments Frits, are absolutely on the money, I would for sure put in several days of intense scrutiny before trying to contradict you , of all people on the InterWeb.

[Frits Overmars]

Your comments Frits, are absolutely on the money, I would for sure put in several days of intense scrutiny before trying to contradict you , of all people on the InterWeb.

Wob, I scrutinize every word you write, but I never manage to find anything I can gripe about

[SwePatrick]

Well, i keep on doing it wrong =)

And also, 'what ever floats your boat'

So why do i do it wrong?
Well, it seemed like it made good power early in the powerband with only the rod and original powerjet.
But it leaned out to much on top, and started to nipping the plugs, letting the engine not respond to ignition input anymore(virtually becoming a rc engine).
I needed to cool things down.

But just adding more on the rod or the original powerjet just made it loose power early, at about 8000-10000rpm, engine bogged off the line.
You see, i can duplicate the power without extra powerjets on the roller, but it doesn´t work at the track when trying to get good 60ft.
And then later going through the gears, it never deactivates as the rpm is above 10500 all the time, working just as a normal powerjet.
I´m touching the issue in video posted below(but with shiftcut), if sitting 'long' on launchcontrol the carburetors flood the engine while the ignition cuts randomly.

Methanol/dragracing life =)

93whp baby! (15% losses is becoming 109.4 at the crank)

[wobbly]

SwePatrick - I will give you a hint that very few people know about, and its never mentioned in so called " jetting charts ".
You said that you had an issue keeping the mid range fueling correct when the WOT fueling was optimum at peak and in the overev.
Well the main jetting components that solely set the fuel curve when at lower rpm and WOT , is the annulus area of the needle tip sitting in the emulsion tube.

Most needles sit about 5mm into the tube , so measure that diameter and the tube diameter.
Using the tip area alone you can go from blubbering rich to deadly lean when within the mid rpm and WOT.

The only caveat is you should end up with the annulus at least 25% bigger than the main area.
Your jet combination must be very wrong as Methanol will happily run at 20 % rich with no effect on power. - making it way easier to find a working setup than petrol.

[husaberg]

SwePatrick - I will give you a hint that very few people know about, and its never mentioned in so called " jetting charts ".
You said that you had an issue keeping the mid range fueling correct when the WOT fueling was optimum at peak and in the overev.
Well the main jetting components that solely set the fuel curve when at lower rpm and WOT , is the annulus area of the needle tip sitting in the emulsion tube.

Most needles sit about 5mm into the tube , so measure that diameter and the tube diameter.
Using the tip area alone you can go from blubbering rich to deadly lean when within the mid rpm and WOT.

The only caveat is you should end up with the annulus at least 25% bigger than the main area.
Your jet combination must be very wrong as Methanol will happily run at 20 % rich with no effect on power. - making it way easier to find a working setup than petrol.

When a Keihin PWK on a Mx 250 or 500 wears oval in the un-replaceable Needle jet, you can use a needle with a much fatter lower section from say a mx125 to compensate. You can also tune the curve with shroud height an low and high speed air jets.

[F5 Dave]

When a Keihin PWK on a Mx 250 or 500 wears oval in the un-replaceable Needle jet, you can use a needle with a much fatter lower section from say a mx125 to compensate. You can also tune the curve with shroud height an low and high speed air jets.

You can pull out the tower and replace the jet with high tolerance insert and replace being careful of airleaks. Or buy aftermarket Stic (?) Replacement tower.

I believe at the start of this thread all those years ago my first post was about dropping the main jet out to prove it can't take full throttle.
Only usually catches you out when putting a very different carb on, say a small engine, but ive seen it more than once.

Methanol could easily see this. But also the cross drilling of the carb supplying the float jet or that orifice itself.

[husaberg]

You can pull out the tower and replace the jet with high tolerance insert and replace being careful of airleaks. Or buy aftermarket Stic (?) Replacement tower.

I believe at the start of this thread all those years ago my first post was about dropping the main jet out to prove it can't take full throttle.
Only usually catches you out when putting a very different carb on, say a small engine, but ive seen it more than once.

Methanol could easily see this. But also the cross drilling of the carb supplying the float jet or that orifice itself.

Yeah I pointed that out to someone the other day re the early post. Although I thought Rob had said it about Thomas. That tuner the ESE brought in to steal your wins at Taupo.
I assume you picked it up from the same place I did (Bell)

I hadn't seen the inserts... it was a design flaw or more likely designed obsolescence I guess

[TZ350]

I believe at the start of this thread all those years ago my first post was about dropping the main jet out to prove it can't take full throttle.

Yeah I pointed that out to someone the other day re the early post. Although I thought Rob had said it about Thomas. That tuner the ESE brought in to steal your wins at Taupo.

No, definitely F5 Dave's idea. Works well too, good check for fuel flow and needle/jet combo being to small.

[F5 Dave]

I think Ram passed that tidbit out during Fish and chips at a GP after match in the 80s, and probably Pete Sales to him and so on.