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 and therefore has little impact compared to +81 ?

And therefore the bump in the pressure trace isn't so concerning?