ESE's works engine tuner

[wobbly]

My instant response is that is a 4 stoke emulsion tube.
With hardly any exception ( a couple of RD Yamaha's ) NO 2T has air corrector holes in the tube - they use a shroud in the bore.
So now we are off on a whole new tangent, especially as you have the issue of the needle/tube combination affecting idle - a major pointer, that should not happen right there.

[JanBros]

yet these carb's are common on 2strokes. I've found a website that sell's replacement dellorto's for all kinds of bikes where all the jet's , needles and tubes numbers are referenced, and they all use these types of tubes. On 1 engine 1 use PHBG's and they also use that type of tubes and on that one everything works just fine.
example's :
Carburateur DELL ORTO PHVA Ø17.5US Honda/ Kymco Scooters 50 2T E2 - Carburateurs - EasyParts.nl - De grootste in onderdelen en accessoires voor scooter en brommer
Carburateur Dell Orto PHVA Ø17.5ED Malaguti Ciak 100 2T 1999-2001 - Carburateurs - EasyParts.nl - De grootste in onderdelen en accessoires voor scooter en brommer

I've tried many combinations of the settings on that site but problem stays. I make my own throttle slides (because I hate the original's where you have to put the cable through a hole instead of just hanging it in through the groove that prevents the slide to turn), but it does the same with original slides.

[Jan Van Hamme]

JVH, there is alot of residual Blowdown pressure, shown by the bump at TPO - this will be reversing flow down the transfers.
I assume this is a function of the single Exhaust port and conservative timing to help front side.

Wobbly, I tried using higher timings today. I can't get rid of that bump at TPO.
I see the same bump in all the graphs on page 2716.
Is there a way to eliminate something like that? I have no idea how to do that.

[wobbly]

JVH, you cannot delete the Transfer bump, unless you have an excessive amount of Blowdown STA.
And having some excess Blowdown pressure at TPO is vital to how transfer stagger actually works.

In your case I was commenting on it due to having relatively low superposition, plus a limited wave peak amplitude before EPO.
In this context the residual Blowdown pressure is quite high, when seen in light of that low pressure ratio amplitude before EPO.
Maybe this is due in part to the fact you are using a huge duct exit diameter, with no steeply tapered slip joint transition up into the header - that pulls down the high pressure ratio at EPO much quicker.


JanBros - using that series of emulsion tubes I have never seen in a 2T before, but having said that I have never worked on the tiny diameter Dellorto's
for scooter type things.
Even the 30mm Dellorto used in KZ racing uses the normal 2T tubes with no holes at all.
Its odd in that in the " Dellorto Motorcycle Carburetor Tuning Guide " they show the two different air corrector systems,
The 2T version has the shroud inside the bore, and an air corrector drilling from the bell mouth that exits into a short well around the needle entry.
Then the 4T version has the corrector air entering around the outside of the emulsion tube, where the size / number and height of the corrector holes changes the fuel curve from part to full throttle.
And I have seen another Dellorto guide showing the two tube types - saying the ones with holes are specifically for 4T

The so called STIC conversion for Keihin carbs uses this principle, and the advertising blurb says it atomizes the fuel droplets better, some swear by it - others swear at it.
With a huge range of tubes having differing corrector hole patterns, dialing in the best response must be a nightmare.

[Vannik]

Wobbly, I tried using higher timings today. I can't get rid of that bump at TPO.
I see the same bump in all the graphs on page 2716.
Is there a way to eliminate something like that? I have no idea how to do that.

Jan, inspect the severity of the bump with both Mach Index (which usually show a large return flow) and with Mass Flow. Usually the Mach Index makes one panic and then the Mass Flow makes you realize that it is nothing to worry about as the physical mass reverse flowing is very small. Bottom line, do not look at the pressure trace in isolation.

[Jan Van Hamme]

Jan, inspect the severity of the bump with both Mach Index (which usually show a large return flow) and with Mass Flow. Usually the Mach Index makes one panic and then the Mass Flow makes you realize that it is nothing to worry about as the physical mass reverse flowing is very small. Bottom line, do not look at the pressure trace in isolation.

Hi Neels,
Do I understand and interpret you correctly that the A-Transfer Mass Flow Rate of -0.86 in that small time span is only a small amount (a small curve area below the zero line) and therefore has little impact compared to +81 ?

If these graphs don't reveal any problems, I'll start building the cylinder and engine.
Currently, my 123cc engine is producing in simulation 36 hp at 10,000 rpm with a flat torque curve.
That's a BMEP of 13.08.
Getting there as a hobbyist is more than enough for me.
I don't have the knowledge yet to improve it further.

[Vannik]

Hi Neels,
Do I understand and interpret you correctly that the A-Transfer Mass Flow Rate of -0.86 in that small time span is only a small amount (a small curve area below the zero line) and therefore has little impact compared to +81 ?

Yes, you understand correctly. I wanted you to see there is more than just pressure traces and also one needs to look at a bigger picture.

[Jan Van Hamme]

Yes, you understand correctly. I wanted you to see there is more than just pressure traces and also one needs to look at a bigger picture.

Recognizing, knowing and estimating which bump is bad and which is negligible in the graphs is the next learning curve for me.

[koenich]

While we are on the topic of carbs...I have a very strange issue with my 50cc Bidalot: if you need to roll off throttle earlier than usual (e.g. slower rider in front of you before a corner) once you go back on throttle the engine stutters around, doesn't pick up revs and feels like it has loaded up with fuel. after few meters it'll clear and ride as usual.

Other than that it's working perfectly fine, any ideas what could help?

[wobbly]

Koenich, as I have been thru the exact opposite of your problem, with a couple of customers who had fitted Sudco 35mm Keihin carbs to LC/YPVS racebikes, the fix becomes quickly obvious.
They, because of ignoring my insistence they use EGT to tune the bikes, found that when backing off slightly into a fast corner, the thing seized immediately.
So, as they had received their ace tuners badge in a box of wheatbix, they decided that the main was too lean.
Result, another seizure.
Do that 3 times, then ring the guy who built the engine.
The correct answer would have been instantly obvious on the EGT trace, if they had bothered to fit a data logger - too expensive apparently , even compared to 6 pistons and cylinders.
Your fix is the dead opposite of what they needed.
In your case when backing off, more mass airflow is reduced, than is the total fuel flow - thus the needle tip diameter is too small.
Increase your tip diameter, and this will reduce the fuel curve sufficiently in line with the drop in mass airflow and that will push the A/F mixture closer toward stochiometric.
Be mindful that the needle tube/ tip diameter annulus area also affects the WOT fuel flow, thus a larger main would be good initial insurance as well.

[flyonly]

Koenich, as I have been thru the exact opposite of your problem, with a couple of customers who had fitted Sudco 35mm Keihin carbs to LC/YPVS racebikes, the fix becomes quickly obvious.
They, because of ignoring my insistence they use EGT to tune the bikes, found that when backing off slightly into a fast corner, the thing seized immediately.
So, as they had received their ace tuners badge in a box of wheatbix, they decided that the main was too lean.
Result, another seizure.
Do that 3 times, then ring the guy who built the engine.
The correct answer would have been instantly obvious on the EGT trace, if they had bothered to fit a data logger - too expensive apparently , even compared to 6 pistons and cylinders.
Your fix is the dead opposite of what they needed.
In your case when backing off, more mass airflow is reduced, than is the total fuel flow - thus the needle tip diameter is too small.
Increase your tip diameter, and this will reduce the fuel curve sufficiently in line with the drop in mass airflow and that will push the A/F mixture closer toward stochiometric.
Be mindful that the needle tube/ tip diameter annulus area also affects the WOT fuel flow, thus a larger main would be good initial insurance as well.

What logger wobbly?


Sent from my iPhone using Tapatalk

[wobbly]

Having used many, my quick answer is a Mychron - 2T, this has been used by Karters forever.
You need the 2T as it allows water temp as well as EGT.
With GPS it draws a track map showing GPS speed, rpm, water and EGT, if you want 2X EGT you need an expansion box.
Its only limitation is the the data record rate is set at 10 HZ , so as Ricky has found we cant log suspension travel as the rate of change is too quick.
We are building a stand alone logger at 100Hz to get this vital information.

[F5 Dave]

I had trouble comprehending that until i reread it.
Just be sure what you mean by backing off verses backing off a little. On a small carb in a 50 small track possibly, does that mean closing the throttle almost completely?

Wobbly is saying winding off a bit which is still constrained by delta of annulus to needle- at that point.
So the question to be sure of is -name your position of needle correctly.

Bikes with too small pilot and large needle base diameter like to sieze on closed.

But on a side note. Beware of the tiny carb that doesn't flow enough petrol into the float to keep it brimmed. Funny shit happens then. Gets exposed on longer tracks or an All gears run on the dyno with tall gearing, any drop in hight gears means you have a fuel flow issue. Played that game too often.

[Storbeck]

For what it's worth I have a two or three generations outdated aim evo 4 that can log at 1000 Hz. I would imagine the newer models are even better.

[koenich]

Thanks for that! Actually have a Mychron incl. EGT - need to look into that, maybe I can find a run where it happened.

Completely closing throttle earlier than normal, however carb is not so tiny at 30 mm and no issue on all gear runs on a dyno which fits very well to our acceleration times on track.

Re suspension - I'm using my Mychron 5S with an Expansion module and even with Aliexpress linear potentiometers works pretty good. Sample rate is 25 Hz, the only thing you need is a math channel which converts mV to actual position since you can't add a custom sensor

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