Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

Chapter 17 - Taillight

Nothing crazy here, just a bracket made from aluminum angle stock. Had fun making it, put in a fresh blade on the hacksaw which made things go quick, added a couple little fancy touches.

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Oh, and here's what the lowbeam looks like. Beam pattern can be seen briefly in the video a couple posts back.

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Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

Chapter 18 - Exhaust Sensors

Needed to add a couple bungs for the exhaust sensors to complete the harness. Unsurprisingly, the EGT bung in the header wasn't the most fun thing to weld due to the heavy rust and tons of carbon buildup, but didn't go as badly as I feared. O2 bung weld exceeded expections, somehow. My hands have always been crazy shaky, and the pipe is a wobbly mess on the welding table, so getting a quick, easy weld on something like that is always a nice treat for me.

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(edited)

Re: General 5-Star Build - Fast 50cc Single-speed

Brandon Weiss (Detective brandon to you) /

Holy moly. I've never heard a more clearly defined pipe hit than that. It sounded like your dropped a gear!

Absolutely nuts, can't wait to see some onboard footage, with a gps please! (To help understand the acceleration you're feeling)

Re: General 5-Star Build - Fast 50cc Single-speed

This shit is dope. Miss having you around mikey

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

Chapter 19 - Small Tuning Woes

> Brandon Weiss (Detective brandon to you) Wrote:

> -------------------------------------------------------

> Holy moly. I've never heard a more clearly defined pipe hit than that.

> It sounded like your dropped a gear!

>

> Absolutely nuts, can't wait to see some onboard footage, with a gps

> please! (To help understand the acceleration you're feeling)

Ha, you're almost in luck! I was planning to make a detailed post about this anyway, so you get the long description before the vid, sorry! It's still rendering anyway.

The gearing is set to top out around 45-50mph. Acceleration was adequate for 50cc, and the test run was ever-so-slightly uphill, not much wind. Pulled hard and then hit a wall at 42mph after about 12 seconds, and started four-stroking/misfiring. This made me suspect main jet was too big, since it should have a few more MPH in it (80 in a PHBG 19, set for my 6000' elevation - stock for the KTM setup is 85).

Since this was just a quick test run, I didn't take the time to swap jets - a wise choice, as I had to climb a ~10% grade, 500' hill to get back home. It was no problem cruising up at 35mph, and it had a little more acceleration left, but the speed limit is 25mph, so I just went fast enough to lock the clutch.

But my assumption of being too rich got a challenge here: things got a little hot on the ride up, about 230F water temp - so maybe a little lean? Pulled the plug, this hill is like a mile long, so should have left a good jetting indicator - it came out almost perfectly clean, almost no carbon deposits at all... huh.

I had also swapped in the Tomar clutch, set at about 10k, because I was struggling to get the jetting in the ballpark with the stock clutch at ~8000rpm on some quick acceleration tests in from the of house a couple days before. It acted like it wanted more fuel at the 8k clutch slip, but then it started 4-stroking at lower-than-normal speed once I revved into the power band. So I figured I would just get it to run on the pipe only with the higher clutch stall and have an easier time jetting it.

I've really been scratching my head hard, though, especially after that long hill climb on the way back from shooting this video. One last symptom: kill button wouldn't stop the bike from idling, until I went WOT while holding the button and it would finally die.

Turns out, there may be a simple answer to all this. KTM used a BR8ECM plug as stock (which I didn't realize at first), and when I got the motor it had a B8HS in there, so I threw in the same before the video and hill climb (and for that initial test run in the previous vid). Some of you probably already see the issue, but I didn't have the head off with the plug installed until I realized the issue. Oops!

Here's how the B8HS looks in the head:

IMG_20190905_110557.jpg

...versus the BR8ECM:

IMG_20190905_110716.jpg

I'm pretty sure I did the same stupid thing on my Peugeot a while back, and had the same annoying tuning headaches. Finally realized I had an "H" instead of an "E," and things got instantly better after swapping. So, hopefully the same thing happens here, and I get better performance. I'm kinda certain I must have been preigniting, too, because of the mostly ineffective nature of the kill button... might have had some carbon buildup on the end of the plug hole that was lighting off at idle?

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

> alex . Wrote:

> -------------------------------------------------------

> This shit is dope. Miss having you around mikey

I miss being around :( Don't tell any of my other old friends this, but my moped friends in Michigan were my favorite friends ever.

Re: General 5-Star Build - Fast 50cc Single-speed

mike, one thing to keep in mind is any exhaust gas pressure in the pipe will cause the o2 sensor to skew its reading.

it's really an issue on turbo setups and not so much on NA rigs, but 2smokes generally run with higher EGBP than most NA setups due to purposefully slow bleedown.

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

Chapter 20 - Wiring Issue

After the quick test run in the previous crappy video, I finished up the wiring. One minor issue with it, that's my own fault: I used pin 87a on the gauges' relay (instead of 87), which I understood to be powered up when you switch off the relay - this seems to be a correct assumption, as the switch worked as I hoped, but there was one issue. Left the battery plugged in, with everything powered down, for a couple days. After a day or so, no problem, still had enough juice that the lights worked, but the gauges seemed intermittent. But when I took the bike out to shoot the upcoming video, the battery had totally died. One of the cells (3S LiPo) is totally gone, couldn't rescue it, won't hold any amount of charge. So no working gauges in the next vid.

As for diagnosing the issue, with everything powered down and no battery connected, the battery terminals had 88 Ohm resistance, and with the switch in the on position, something like like 15k Ohm - oops, that's a 130mA draw when everything is shut off, meaning the 5000mAh battery would last about a day and a half with everything powered off! Must be that by using 87a, the relay routes power to the gauges when its coil is off - i.e. when I turn off the gauges, I'm powering the switching coil in the relay.

Should be an easy fix, just swap the connector to the 87 slot in the relay holder. The reason I used 87a in the first place was so my switches were all "down for off" because the gauge switch had to be upsidedown to fit between the gauges. So no biggie.

Video has a few more minutes to finish uploading, so coming soon!

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

> ken gilbert Wrote:

> -------------------------------------------------------

> mike, one thing to keep in mind is any exhaust gas pressure in the pipe

> will cause the o2 sensor to skew its reading.

>

> it's really an issue on turbo setups and not so much on NA rigs, but

> 2smokes generally run with higher EGBP than most NA setups due to

> purposefully slow bleedown.

Ken, I think the bigger issue for high-power 2-strokes is that the sensor doesn't read AFR directly, it literally measures oxygen content. Especially when you're not on the pipe, there is significant blow-through/short-circuiting of fresh mixture (read: oxygen) through the exhaust port, which will cause it to read super lean, even if you're running rich. And like any engine, 2- or 4-stroke, if you run so rich that you have some misfiring, perceptible or not (like when you're on the edge of 4-stroking), the gauge will read dead lean due to the unused oxygen.

So I'll mainly be using EGT to tune, as well as seat-of-the-pants/sound/experience, as well as acceleration data from the GoPro. O2 is the least helpful parameter due to its 2-stroke limitations, so it's mostly just for curiosity :)

The GoPro GPS data isn't terribly accurate, and the accelerometer data is noisy, but I'm working on a Kalman filter that uses both of them to get a nice clean signal. With some assumptions regarding aerodynamic drag (taken from empirical data from a few sources to get in the ballpark, which is good enough for comparing two jettings), and using the same almost-flat test ground as the upcoming video, I can get a reasonably accurate estimate of power to the wheel. I'll have more on that soon, once I get the Kalman filter sorted a little better.(edited)

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

...and here's the aforementioned video. I need to do a little more work on processing the data to extrapolate power, but some initial calculations show about 5hp to the wheel, maybe 2.5ft-lb torque while the clutch is slipping (there's about 20% less air here than at sea level, so maybe around 6hp corrected).

That's lower than it should be for this engine, but this was with the wrong-length spark plug, and what felt too rich (but probably just crappy ignition). I think for future runs, I'll use the same stretch of road, it's about as flat as it gets here, a little uphill, but probably less than 1% grade. I'll try and do it when there isn't wind, but with the current gearing those factors are minimal. Hopefully another couple runs today, which I'll film for comparison data after the plug and after (hopefully) getting the jetting dialed in.

I'm using some PHBG clone at the moment, and it's not the best ever, but I've got a real one on the way from Treats with a few needles and a smaller atomiser (going to start by copying the stock KTM jetting, adjusted for altitude, and go from there).

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

For those that want to nerd out, here's how I've come up with that 5hp number.

First, I applied a simple Kalman filter to each axis of accelerometer data - I suppose it's a 1-D filter, with an adjustable parameter for sensitivity. There's still some noise in the data, but smoothing it out much more led to inaccuracy. Here's what the raw data for all three axes looks like, for reference:

RawAccelData-2019-09-03.png

After filtering the raw accel data, I subtracted out Z-axis (vertical) and Y-axis (longitudinal) steady-state readings. I got these by averaging about 20 seconds of the top-speed portion of the run. The camera was mostly upright, but tilted forward enough that the Y readings were about 4m/s/s steady-state. Also, this means that my acceleration (from going WOT) was registering on both Z and Y axes. I then combined the Z and Y axis data, where total = sqrt(z^2 + y^2). This gave a pretty reasonable approximation of the acceleration.

From there, I did a wild guess on total weight, I said 127kg. I'm 180lb, I assume the bike is a bit more than 100lb. Anyway, close enough for mopeds. Since F=ma, I can then calculate the force for the acceleration. Since Power = Force * velocity, and I have the GPS speed data, I can calculate the power required to give that acceleration. Note that this is actual power to the wheel - even though the engine is at 10,000rpm at launch and probably making ~4hp, NONE of the power gets to the wheel when you're not moving (since velocity is zero!). It all is going to heating the clutch. The torque, however, is easily calculated from the acceleration-derived force, using tire radius, sprocket sizes, and primary reduction (total gear ratio is about 21:1 right now).

I'm not going super fast, but there is a bit of aerodynamic drag involved, too. Using some rough empirical numbers, I used 0.675m^2 for frontal area, and 0.65 for Cd, giving a 0.44CdA value. Used the conditions of the day to estimate about 0.7kg/m^3 air density, and Drag = 1/2 * density * velocity^2 * CdA. Multiply by velocity again to get power. Add drag power to the acceleration power to get total power to the wheel.

All calculations are summarized in this plot:

1DKalman-2019-09-03.png

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

As a sanity check on that drag calculation, a stock "2hp" moped does about 30mph. I've calculated about 1.5hp (at the ground) for going 42mph - not totally out of the realm of possibility, considering that 2hp moped might do closer to 35mph with a gearing change, and I assume 2hp means at the crank. If anything, my estimate is a bit conservative, meaning my power estimate may be sandbagging a bit.

In any case, this methodology should be good enough to compare better than the butt dyno.(edited)

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

...and with that, this thread is up to date. Here's how the bike currently sits, all wiring installed and everything. Will get painted at some point, but I'm sure I have more welding to do, somewhere.

Low enough to fit in the Land Cruiser for when I do more distant tuning sessions:

IMG_20190902_151427.jpg

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

Swapped the spark plug, tried again. Ended up dropping down from 80 main jet to a 75 (supposedly, it's from the clone carb so who knows).

Crunching the numbers shows close to 6hp now vs 5hp, and a solid improvement in average torque during the acceleration phase, from about 2.2ft-lb to 2.9.

Still doesn't seem to want to rev out as much as expected.

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

And here are the crunched numbers. Used GPS speed data to calculate acceleration, instead of the accelerometers, otherwise pretty much the same methodology. Significant improvement from changing the plug and maybe a little better with downjetting too. The BR8ECM data was with a strong headwind, for whatever that's worth.

Oh and sometime around when I shot that video, the rear mount for the pipe failed... the braze held, but the steel tab broke. And I think my header o-ring might be toast, so may have a header leak. Time to order the real-deal KTM o-ring and not use Harbor Freight (hey, I wanted to get it running!).

BR8HSvsBR8ECM.png

(edited)

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

Pipe is back on the bike, and swapped back to the stock clutch with Mini Adventure springs for a 5000rpm slip. Forgot to torque the bolts on the clutch shoes, got locked up a couple blocks from home, oops. No damage thankfully! I kinda like the low clutch stall. Makes things really fun when it comes on the pipe, even with crappy carb tuning at the moment.

Also got a real PHBG from Treats to help with the tuning. Seems pretty rich overall, with jetting taken from the KTM stock settings and adjusted for altitude (6400'). 80 main jet, 40 pilot (stock is 86 and 45, I think). W9 needle right now with 262AU?

I don't know if I trust my super cheap EGT gauge (waiting for another probe to double check it), but the bike feels/sounds rich and EGT only hits an indicated 450C at the most when it's on the pipe. Gonna downjet tomorrow and see how it does.

Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /

Popped in a W11 (I think? 1.80mm tip, vs 1.40mm previous) needle, a 32 pilot, and tried 80 main (vs last attempt at 69, too lean up top, lost power).

The reason for the needle and main jet change: it was running rich at WOT at lower RPM, and lean up top. Now, this was news to me, but revalatory: according to Wobbly over at KiwiBiker, your main jet DOES NOT control WOT at lower RPM if it's in the ballpark - that's up to the needle tip diameter and needle jet! With a 260ish needle jet and 1.4mm-ish needle tip diameter, you end up with a huge annular area in comparison to the area of a 80ish main jet. Like roughly 5x the area. You get an extra boundary layer that slows the flow down a bit (the needle). Apparently you can pull the main jet out of the carb, and if your needle is right, you can go WOT up to some set RPM, at which point the main jet takes over and you'll get too rich.

This concept worked, quite well. FINALLY I got some heat in the pipe. Hadn't seen it exceed 450C, ever, before this. Almost got up to 700C at one point, with a good amount of time at 600-ish. Target zone is apparently around 650. Going WOT cooled it down a little, so may need to go down a touch on the main jet.

Definitely the best the bike has run so far. Will get a new video soon.

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