ESE's works engine tuner

[Peter1962]

Wob, to console you, here is proof that I also make mistakes. For example, yesterday, when I didn't get around to congratulating you on your birthday (I was rather busy in a Ferrari on a nice German racetrack, the Lausitzring). So here you go, to your health, Wob. And to mine, because traditionally my birthday is one day after yours.
356539

Happy birthday to you and to wobbly !

yum yum, Hendrick's is great !

[wobbly]

1-2-4-5-3 minimizes the rocking couple, in theory.
As used by Audi, VW and Volvo.
Myself and a mad mate built a 5cylinder H1 Kawasaki with this and it felt fine, long before Millyard.

[Jan Van Hamme]

Hi, when designing a cylinder 3D printing project, I'm unsure of the minimum recommended distance between the A transfer and the main exhaust port.
Is 5.57mm sufficient for a full FOS transfer concept with all the associated scavenging angles?

I'm also considering rounding the piston according to the recommended dimensions on FOS OneDrive.
I’m using a Wössner 8302D200 piston for a YZ125 2005-2021 for this project.
If I apply the radius, will the remaining 1.56mm still be thick enough?

Regards, Jan

[Viking]

I'm not a Viking but I am pretty sure he's using 670 Rotax cylinders that look a lot like this (pictures from ebay ads I found on the interweb).

The experts can opine if those are lift shafts, to me they are not the MOST squared off lift shaft transfers I've ever seen....but they don't look much like a teacup.



Unexpected happening. I found a cut Rotax 670 cylinder in my office.
A-transfer duct and B-transfer duct almost similar.
Exhaust duct length 60mm and diameter 45mm at flange interface.

[Wos]

Hi, when designing a cylinder 3D printing project, I'm unsure of the minimum recommended distance between the A transfer and the main exhaust port.
Is 5.57mm sufficient for a full FOS transfer concept with all the associated scavenging

angles?




I'm also considering rounding the piston according to the recommended dimensions on FOS OneDrive.
I’m using a Wössner 8302D200 piston for a YZ125 2005-2021 for this project.
If I apply the radius, will the remaining 1.56mm still be thick enough?

Regards, Jan

If you do it from scratch, why dont you take a domed, single ring piston?

Cant remember any advatage of the flat ones...

Then positioning ring gap in the middle of c port...you are more free doing minimum bridges between b and c ports...

Have a look at oler yamaha yz pistons
Or on suzuki rm 125...we use wössner too..

Exhaust t port?...the bridge is a weak point...not as sturdy as triple port layoutļ

Just my two cents ��

Wolfgang

[Jan Van Hamme]

If you do it from scratch, why dont you take a domed, single ring piston?

Cant remember any advatage of the flat ones...

Then positioning ring gap in the middle of c port...you are more free doing minimum bridges between b and c ports...

Have a look at oler yamaha yz pistons
Or on suzuki rm 125...we use wössner too..

Exhaust t port?...the bridge is a weak point...not as sturdy as triple port layoutļ

Just my two cents ��

Wolfgang

Hi Wolfgang, thanks for your reply.

It's an RD125LC. I've chosen to limit my rpm to 10,000 rpm.
If I cut out the bottom of the skirt (like with the old YZ125H), there's not much support left against piston tilt.
I'm thinking of making my own windows (two or three).
That way, I'll have some surface area left over to provide support against tilting.
That's why I opted for two piston rings, for the engine speed and a bit more resistance to rattle.

It's a VHM connecting rod (110 instead of 105).
I haven't found any 56mm pistons with two rings, a dome, a 15mm pin diameter offset by 1mm, and a lower compression height that I can shorten or drill holes in (cylinder intake reed valve).
Wössner did have them. That's why I was forced to use the flat piston.
The plan is to install a torroid insert.

On this piston, the ring gap of both piston rings is in the center of the C port. One is directly in the center, the other a millimeter off center.

A single exhaust port (70% and safe roof) is sufficient for blowdown and low timing for the intended power and rpm.
Therefore, I would opt for a T-port or triple exhaust port.

I'm not sure if the distance between the exhaust and the A-port is large enough to prevent shortcutting.

Vriendelijke groeten,
Jan

[Wos]

Hi Wolfgang, thanks for your reply.

It's an RD125LC. I've chosen to limit my rpm to 10,000 rpm.
If I cut out the bottom of the skirt (like with the old YZ125H), there's not much support left against piston tilt.
I'm thinking of making my own windows (two or three).
That way, I'll have some surface area left over to provide support against tilting.
That's why I opted for two piston rings, for the engine speed and a bit more resistance to rattle.

It's a VHM connecting rod (110 instead of 105).
I haven't found any 56mm pistons with two rings, a dome, a 15mm pin diameter offset by 1mm, and a lower compression height that I can shorten or drill holes in (cylinder intake reed valve).
Wössner did have them. That's why I was forced to use the flat piston.
The plan is to install a torroid insert.

On this piston, the ring gap of both piston rings is in the center of the C port. One is directly in the center, the other a millimeter off center.

A single exhaust port (70% and safe roof) is sufficient for blowdown and low timing for the intended power and rpm.
Therefore, I would opt for a T-port or triple exhaust port.

I'm not sure if the distance between the exhaust and the A-port is large enough to prevent shortcutting.

Vriendelijke groeten,
Jan

Ok jan ;)

I stuck with bore of 54.5 for a 125cc

But we run a 125 with adaptet reed valve to cilinder that has down skirt a cutout...and 2 Windows to, with only one ring...absolutely no problem...the wössner is stiff enough...35 h no ploblem


...doing a printed cilinder...wow :) ...dont you think about changing bore and stroke to square?
...every kind of pistons avaiable...and next to best bore stroke ratio...

Some Pages earlier frits gave a rule of thumb, about minimum space between ports...

Formula was bore x 0,044

If this rule is applyable to bridge between Ex and A port...you should be save ;)



Keep us informed about...especially printing your dream cilinder! ;) ;)

Wolfgang

[diesel pig]

Ok jan ;)

Keep us informed about...especially printing your dream cilinder! ;) ;)

Wolfgang

I would like to second that. Please keep us informed about your project. Metal printing is very interesting!

[Jan Van Hamme]

Ok jan ;)

I stuck with bore of 54.5 for a 125cc

But we run a 125 with adaptet reed valve to cilinder that has down skirt a cutout...and 2 Windows to, with only one ring...absolutely no problem...the wössner is stiff enough...35 h no ploblem


...doing a printed cilinder...wow :) ...dont you think about changing bore and stroke to square?
...every kind of pistons avaiable...and next to best bore stroke ratio...

Some Pages earlier frits gave a rule of thumb, about minimum space between ports...

Formula was bore x 0,044

If this rule is applyable to bridge between Ex and A port...you should be save ;)



Keep us informed about...especially printing your dream cilinder! ;) ;)

Wolfgang

You're absolutely right. I'd read in Frits' columns and OneDrive that oversquare engines aren't good for two-stroke engines (though they are for four-stroke engines).

So I looked into making a crankshaft with a 54,5 stroke instead of a 50-stroke, which, as you rightly point out, would also allow a wide range of pistons to be used.

The original crankshaft webs are 87,8mm in diameter. The crankcase has a 89.8mm diameter.
I'd have to mill out the crankcase to make room for the increased stroke.
This would put me too close to the holes used to hold the crankshaft halves together. There wouldn't be enough "meat" left there after the milling.
So, there went my hope of making a crankshaft myself to square up the engine.

I'd read on other forums that the auxiliary exhaust ports on the RSA only came very close to the A transfers over a very short distance.
They wrote that it was very critical to make that close-in zone longer. It was also pointed out that the distance between the main exhaust port and the A transfers needed to be much greater.
I looked at photos of an RSA cylinder, and they do indeed stay far away from the main port. How far?
As you rightly mentioned, I also noticed that Frits explained that formula a few pages back.
Because of those earlier photos and the larger distance at the RSA than the formula, I started wondering... would 5.57mm be enough?

By creating a 3D-printed cylinder, I'm trying to combine everything I've read over the years by Jan Thiel, Frits Overmars, Wayne Wright and try to apply it by and with Engmod2T from Neels Van Niekerk to the possibilities and limitations of an RD125LC.
As a hobbyist, I'm sure there will still be many obstacles in my project.

Working on my motorcycle like this makes me realize how incredibly impressive the knowledge and experience these people possess, what they've developed and achieved.
As I once wrote, their combined experience could fill an entire galaxy.
I haven't yet reached the level of the first ridge on their shoe soles (and for some, even their sandals). Nor do I have the ambition to do so.
I'm glad they, and people like you and others, are helping me through this digital means.

Groeten Jan

[bad'rule]

Re: Wos,
Have you checked on DT125E piston

Sent from my RMX1911 using Tapatalk

[Jan Van Hamme]

Re: Wos,
Have you checked on DT125E piston

Sent from my RMX1911 using Tapatalk

A DT125 has a 16mm piston pin diameter.

My VHM connecting rod has a small-end bore for a 19x15 needle bearing.

19x16 doesn't exist. I briefly considered filling the space with loose needles or using adapter bushings, but I opted for a commonly available silver-caged needle bearing measuring 19x15x19,5.

Groeten Jan

[Wos]

125 lc is without ypvs system?

All parts for are still available...:drool: ��

Yz 125 1983 had powervalve too...

https://mxlocker.com/product/1983-yamaha-yz125-oem-cylinder-24x-11311-00-00-565-mm-bore-y-ITDol

[Jan Van Hamme]

125 lc is without ypvs system?

All parts for are still available...:drool: ��

Yz 125 1983 had powervalve too...

https://mxlocker.com/product/1983-yamaha-yz125-oem-cylinder-24x-11311-00-00-565-mm-bore-y-ITDol

It's an RD125LC-10W. They don't have a power valve.

Because of the higher power I'm aiming for, I wanted a stronger, yet lightweight connecting rod.
I ended up with a VHM connecting rod. So the standard piston parts from a DT or RD won't fit.
The footprint of a YZ125 cylinder doesn't fit on my crankcase.
I also want the cylinder to look like the original on the outside.

I've already bought the VHM connecting rod, three Wössner pistons, and needle bearings.
Thanks for the input, but my main concern is the distance to avoid an exhaust shortcut.

[Wos]

Chance to adapt the ypvs to your print 😉

[wobbly]

JVH, as your engine will be developing a low bmep, the pipe diffuser will be nowhere near SOTA, and thus will not be generating a huge depression around BDC.
Honestly I dont think you need to be worrying about short circuiting, as long as the A port front wall is radially pointing sufficiently back toward the boost port.

[Jan Van Hamme]

Honestly I dont think you need to be worrying about short circuiting, as long as the A port front wall is radially pointing sufficiently back toward the boost port.

That's the answer I needed to clear up my doubts and concerns and move forward with my Solidworks design.
This is the exhaust I'll be using. It's not the same as the one I uploaded in my Pack file to the Engmod2Tgroup.
Thanks again

[wobbly]

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.

[JanBros]

a question about carb's. I have 4 engines for my MX-mopets, and now I've bought a whole lot of used incomplete Dell Orto PHVA and PHBN carb's very cheaply- over 20 of them, enough to make spare carb's so I have for each engine at least 2 identical carb's so I can quickly swap them when we are having carb troubles during races.

Since I had to put everything together myself, I had to figure out all the settings myself, and the ones I've selected are working fine, except one thing gives me some troubles : when closing the throttle after full open and the engine needs to come back to idle, they keep idling at arround 2700rpm , allthough after starting and warming up they idle fine at arround 1600. stop the engine and restart immediatly and they idle fine again. I've tried idle jet's from 30 to 40, throttle slide cuts from 10 to 50, different needles, but on some carb's the problem stays . but they work fine when the mopeds are racing.

anyone have an idea of what exactly is the cause of this and how to fix it ?

[wobbly]

A carb " hanging up " above idle after reving is always one of four things.
First is the idle circuit is too lean, where is the idle air screw set ? It should idle and instantly transition best between 1 1/4 and 1 3/4 of a turn - outside this range the pilot needs changing.
Second is the throttle cable has insufficient free play - I like at least a couple of mm of movement on the cable end inside the adjuster screw.
Next is that when reving it, the fuel level is dropping due to the float valve being too small, thus leaning out the fuel ratio. Once the bowl fills again at idle with no load, it returns to a normal A/F.
Lastly is the possibility that once the engine is warm, it has a case leak thru a gasket or seal.

[JanBros]

A carb " hanging up " above idle after reving is always one of four things.
First is the idle circuit is too lean, where is the idle air screw set ?
depends on the idle jet : small ones almost full in, big ones full out. the 30 was too small, the 40 way too big.


Second is the throttle cable has insufficient free play - I like at least a couple of mm of movement on the cable end inside the adjuster screw.
I'll check
Next is that when reving it, the fuel level is dropping due to the float valve being too small, thus leaning out the fuel ratio. Once the bowl fills again at idle with no load, it returns to a normal A/F.
I'll check the fuel flow, but I'm just over 9BHP with the 70's (at +/- 8500), so they are not exactly in need of gallon's of fuel.
Lastly is the possibility that once the engine is warm, it has a case leak thru a gasket or seal.
I don't thinck this is the problem, as it's on more than 1 engine, even on engines that have raced a couple of 4-6h races without any problem's.

It should idle and instantly transition best between 1 1/4 and 1 3/4 of a turn - outside this range the pilot needs changing.
it responses to the air screw, but it might be (so not sure) that the problem is I do not find settings that allow the slide to go down enough and somehow the needlejet is also influencing the idle mixture. could the problem be the mixture tubes ? as I have many different ones and selected the ones that were most common (so swapping them out) so I could have carb's with everything exactly the same for each engine. mostly I'm using the 209GN mixture tubes.
https://sbd.etailercdn.de/media/pimg/l/-/thumbs/290292_2583276.jpg

[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 (https://www.easyparts.nl/Carburateur-DELLORTO-PHVA-%C3%9817.5US-Honda-Kymco-Scooters-50-2T-E2-p16281211)
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 (https://www.easyparts.nl/Carburateur-DellOrto-PHVA-%C3%9817.5ED-Malaguti-Ciak-100-2T-1999-2001-p33842063)

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

356583.

[Wos]

"

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. "

My guess for koenichs problem

Idle jet to big/ rich

and/or

cutaway to small/ rich

This may dropp pipe temperatures maybe so deep, that pipe is out of resonance !?

Next depending issue could be, that rpm s are dropping to such a low level, where ignition advance is high and this is resultig in another lower egt :( ...trapped in double issues!???

Wobbly ? He uses a pwk type carb... without tps...only 2d ignition curve

are these other possible reasons for phenomenon??

Thanks for advice, opinion and help ! :)

[wobbly]

The Mychron 5 needs an Expansion Box to run suspension position sensors , and according to its manual this has a set sample rate of 10Hz.
How do you get 25Hz, but apparently even this will not detect chatter as its way too fast a rate of change.
Aim has a software update that allows a Fourier Transform into the first derivative of velocity, but according to their own information we need up to 500Hz to see
high speed rate of change correctly.
https://www.datamc.org/data-acquisition/suspension-data-analysis/histograms-and-suspension-velocity-analysis/

Re the jetting issue - it was not obvious at all to me that following a slower bike you would " back all the way off ", but anyway, surely the idle and transition jetting has been tuned
such that there is no issues at idle or on initial acceleration.
Im guessing that you have tuned the main, on the dyno, or on the track to suit the bowl fuel level height after a period of WOT.
In the circumstance you describe, maybe the bowl level is dropping at WOT, and when you back off, as no fuel is being used - the bowl refills back to its nominal height and then when
cracking open the gas again the fuel curve is way rich.
This means the float valve is too small - Easy to check by adding a small breather fitting into the bowl nut and running a tube up the side of the carb.

I had that exact issue using Lectron HV40 carbs with clear bowls on a TZ400. On the dyno when hitting WOT you could see the level drop all of 20mm by the end of a dyno run.
The carbs had 3mm valves, fitting the so called high flow 3.5mm versions with side squirt holes, the issue went away instantly.

[F5 Dave]

An age ago on a mikuki i tried bigger valve etc to try solve a problem where upright you could just make it to the end of straight at Ruapuna B but would die as soon as you opened the throttle after the corner.
I ended up soldering an extension on the bottom of the button style jet in frustration. That fixed the symptoms kinda.
But the real reason turned out to be that the cross carb drilling was the actual bottleneck.

Once that was drilled out (and plug the brass ball again) normal jets could be run.

And that wasn't the last time I encountered that.

[koenich]

True - it's only 10 Hz and yes you need the expansion to add analog inputs, for the basic setup (and if you're not really good with interpreting the data) it's plenty capable in my opinion and was my "budget" solution compared to the likes of a MXM or others with high resolution. To get the velocities I added a math channel with the first derivate of position and it easily went up to 400 mm/s - which either way is too much acc to the information I could gather.

Guessed right - all circuits have been tuned, main been done on the dyno. it rides perfectly rolling on the throttle out of corners, main seems to be spot on as long as I'm on my pace. As its a 50cc obviously WOT is used quite a bit so your theory makes sense and thats also what I feel - that it's uber rich if I'm not pinning it till braking point but rather coasting. I'll check that - thanks :)

[wobbly]

As I understand it now, even if we see a full stroke dive under brakes at 400mm/s in 1/10th of a second, then there will be only two data points, the start position velocity, and the end position.
With chatter there could easily be 4 or more cycles, up and down in that time frame, with no intermediate data points to show this.
Thus only one peak velocity point will be displayed, instead of what is actually happening - the front wheel going spastically up and down at a high frequency above the sample rate.
In the digital world the Nyquist–Shannon sampling theorem, states that to accurately capture a signal, the sample rate must be more than twice the highest frequency present, thus I can absolutely believe
that to display high frequency cyclic position changes that 200Hz could be regarded as a minimum.
Doing the sampling and data logging is easy with a cheap stand alone processor board - but then integrating that into the Mychron with a CAN line is beyond me.

[koenich]

Well explained, found the same answer while trying to understand the limitations of my setup in the last days.

Besides the MXm there is also the option to use a Solo 2 DL with an AiM Analog to Can Converter which has a sampling rate of 200 Hz.

[Storbeck]

As I understand it now, even if we see a full stroke dive under brakes at 400mm/s in 1/10th of a second, then there will be only two data points, the start position velocity, and the end position.
With chatter there could easily be 4 or more cycles, up and down in that time frame, with no intermediate data points to show this.
Thus only one peak velocity point will be displayed, instead of what is actually happening - the front wheel going spastically up and down at a high frequency above the sample rate.
In the digital world the Nyquist–Shannon sampling theorem, states that to accurately capture a signal, the sample rate must be more than twice the highest frequency present, thus I can absolutely believe
that to display high frequency cyclic position changes that 200Hz could be regarded as a minimum.
Doing the sampling and data logging is easy with a cheap stand alone processor board - but then integrating that into the Mychron with a CAN line is beyond me.


Apologies if everyone is already well aware of it but rather than starting with a dash/display and adding an expansion, one can start with an evo4s and add a display and have much more capable data logging, 5 channels at 1000hz plus you can still use the expansion through CAN to get more if needed , for sort of around the same cost (a bit more but not huge increase), and still be in the aim ecosystem of software if one is already familiar/comfortable with it.

https://discoveryparts.com/products/aim-gs-dash-and-evo-4s-data-logger-dash-display-w-gps?variant=43645960782043&gad_source=1&gad_campaignid=21067563027&gbraid=0AAAAApOP0ApvZUYReIuv4xUf4aYthrIHQ&gclid=CjwKCAjwq9rFBhAIEiwAGVAZP8jpNSxC4EFKAIOpMnPx hHyRIgUf2uJMDT1zP-I6qnjNbKfk2yiQqBoCQlQQAvD_BwE

For the budget conscious the now outdated "evo 4" (note the lack of an "S") are out there pretty cheap used as people are upgrading. It uses the previous generation software, but still gets you 1000Hz. My opinion these things are an unbeatable bargain if one wants to get into datalogging on a budget. I don't recall but I think the gps updates more slowly on the old evo4 which could be a problem if track mapping is really important to you.

https://www.ebay.com/itm/127304812034?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&mkscid=101&itemid=127304812034&targetid=2512152189032&device=c&mktype=pla&googleloc=9019701&poi=&campaignid=21214286338&mkgroupid=161030074701&rlsatarget=aud-1314496317547:pla-2512152189032&abcId=9407521&merchantid=6296724&gad_source=1&gad_campaignid=21214286338&gbraid=0AAAAAD_QDh_APNYBeXFFgQCoWsRAx3LSA&gclid=CjwKCAjwq9rFBhAIEiwAGVAZP94s-glnrqiIt8CMc_WTTYopY9q3yjBaRZzf7OPdoBIaCttIR5K40ho CZSAQAvD_BwE

[wobbly]

Several racebikes I look after already have the Mychron 5 2T with expansion to run 2X EGT - so I am looking for the most cost effective way of getting suspension data into
that package.