Modern Vespa

Hey Gang, I know this one isn't a Vespa but since the engine from a GTS 250 is in the frame and its running Megasquirt EFI I figured you all might be interested in it, and I hope you'll forgive me for sneaking a not quite Vespa in here...

I bought my Buddy, an orange 125, in 2008. I commuted on it daily and racked up a ton of miles on it. As I do with nearly all my vehicles I started to modify it. Back when I started there wasn't much in the way of performance information for the Buddy, so I started to forge a path to crazier and crazier motors. My 125 became a 161cc then 180cc (long before Genuine released a 170!), clocking in insane speeds and crazier parts. Finally one day around 2012 my poor little Buddy told me it had had enough and cracked a crankshaft on the motor. That was the end of that poor motor.

I picked up a used Vespa GTS250 engine and began the crazy task of grafting it into the Buddy's little frame. The project was going well until I got to electronics. I discovered that the GTS had an immobilizer system that I did NOT have the keys for, and Vespa would not sell me new ones back then. This brought my project to a screeching halt and the poor Buddy was stuck in the back of the garage destined to never see the light of day again.... Until a couple weeks ago...

I had just completed doing a Megasquirt ECU install on the Porsche motor in my 1980 VW bus and it popped into my head like a spectre of the past that Megasquirt can run almost anything, including my GTS engine. Out from under the pile of cardboard and dust I pulled out the long sleeping Buddy and evaluated where it was at.



It was a bit sad looking and I had misplaced some parts in the 10 years its been sitting, but it was mostly there. After some tests I discovered the GTS motor had VERY low compression (60psi) and likely needed a top end... eBay provided a bigger top end and my 250 became a 282cc. Two days of tinkering with wiring and a Microsquirt I had handy, and we had our first start!!

Since the Buddy is aircooled originally I had to figure out how to setup a radiator, and decided to attempt to rear mount it like some of the custom motorcycles do.



After getting some hardware to mount up the wheel I got to see how it would sit on it's own two wheels. It got a fair bit longer, but I don't think it looks bad that way.



I then got the cooling system all plumbed and tested. I don't yet have the correct fan for the radiator so I made due with a PC cooling fan. It worked. Kinda. The cooling fan didn't put out enough air to run it for a long time, but I could run it for 5 minutes or so before it started getting hot. Plenty of time to do some initial tuning!

Part of that tuning involved swapping the engine's stock narrowband O2 sensor for a wideband, which I had handy. This lets me see the exact air/fuel mixture ratio for tuning. Which means its no longer running pig rich with my guesstimate initial fuel table settings.



I Also got the charging system working, replaced the bad starter solenoid so you can actually start it with the starter button now, and replaced the seized front brake master cylinder so it'll stop when its ready to go.

Finally, after waiting for the radiator fan and a few more parts to show up, I got the bodywork all back on and for the first time in 10 years, its left the back patio and runs and rides! I took it for the first spin around the block its had in a decade this afternoon. I forgot how crazy small that bike is! Its not finished, it needs a few bits still, and a lot of tuning. It already seems like it wants to kill me... I tapped the throttle JUST A HAIR. And it spun the rear tire while moving. This is gonna be an interesting bike..



Now onto tuning! The Megasquirt seems to run the engine REALLY well, I have full control of the fuel and spark maps, and can tune all sorts of things anyway I want. It'll be a bit of a challenge to laptop tune it while riding around. But I'll figure out something!

Thanks for coming along on this little nostalgia trip with me!

fantastic. would like more ecu info. what sensors were used to make it work.

Sure! I used the microsquirt variant of the ECU as it's much smaller and waterproof. I used a MAP (Manifold absolute pressure) sensor from GM that's used on nearly all their vehicles, as well as an intake air temp sensor from GM. I built a calibration map for the stock coolant sensor, used the stock crank trigger, and an Innovate LC-2 wideband O2 sensor. I'm currently using the stock throttle body, but may swap out for another as I'd like to have a throttle position sensor and the stock TPS is part of the stock ECU. I also swapped out the coil with one from a Corvette so I could do logic level triggering and get a hotter spark, but the stock one could be used as well.

Very cool – much greater than when we all upped our Buddy 125's to 161cc – it would wheelie with the 161cc – could just imagine what it will be like with such a big motor the frame might need bracing; brakes.
Have fun – be safe.

Yeah, it makes the old 161cc feel like it was standing still. I took it out for its first REAL ride more than around the neighborhood this afternoon, and its a beast. I already upgraded the brakes to NCY calipers and vented 220mm discs, but I MIGHT go even farther and add 4 pot calipers.

Its a bit squirrely, it'll wheelie with the twist of the throttle at *ANY* speed. I found that out by blipping it at 50 and lifting the front!

I'm on the fence about frame bracing. It absolutely flexes when you get on it hard, but its right on the edge of being acceptable flex. We'll see once I get a few more miles on it... But it might end up needing it.

Would love to see more about how the wiring was set-up, wiring colors, etc. I was working on my on microsquirt conversion, but never got around to testing it (I got sidetracked by potentially using the OEM ECU: DIY Diagnostic tool for injection Vespa's with MIU ECU (Page 3)

Care to share the table for the coolant sensor also?


external TPS on stock throttle body - modified kit from a Weber carburetor

MAP sensor plugged into original charcoal canister port, IAT in OEM intake tube

I want to ride it..looks like a blast

Very cool! Thanks for sharing it here 👍

I'll have to pull some of my body panels off to get the colors, but the Microsquirt harness has all the wires labeled so its pretty easy to know which is which.
Here's a "in progress shot of when I was getting it all setup:



The coolant table is as follows:

0° = 5900 Ohm
+10° = 3800 Ohm
+20° = 2500 Ohm
+30° = 1700 Ohm
+80° = 300 Ohm

All in celsius.


I like how you did your TPS, I'd be interested in how that worked. I opted to go without a TPS, and just used my MAP sensor for throttle detection.

Its a SUPER blast, and a bit scary. Its got so much go!

Thanks for the table.

I should have made the adapter bracket out of steel, as the aluminum could flex a little bit... not enough to effect running but it could be bent too easily and throw off the calibration. I never got to the point of running the motor, but I did bench test the TPS and confirmed it worked perfectly. The keyway was a little too small and required some filing to get the fitment correct. Also this would be a little difficult to install, as I think the TPS needs to go on after the throttle linkage.

It's a Weber DCOE TPS kit that I paid way less than what I'm fining online now: https://www.amazon.com/WEBER-DCOE-THROTTLE-POSITION-SENSOR/dp/B07N31DT94

Here's what comes in the kit:

Awesome! Thanks for that! If you ever get back to it let me know, as I've worked out all the stuff you'd need to get it started like crank sensor angle and ignition and fuel tables and such. My tune would be a LITTLE different because I've got the big bore cylinder and a less restrictive airbox, but it would certainly be close enough to get you going.

Thanks for the offer, your tune might actually work out OK as I am far from stock also: 275cc (on a 250), Malossi head, Polini cam, port-matched PM exhaust... doesn't run very good on the stock tune as expected. I haven't given up on re-tuning the factory ECU yet, but haven't worked out a good way to dynolog it (and I haven't actually written to the ECU yet).

My thoughts on the Microsquirt were to have it only control the fuel and possibly timing, as I believe the original ECU is needed to run some of the functions on the dashboard (my motor is still in a Vespa). I have a wideband sensor already, with a narrowband converter to try and keep the factory ECU happy (it doesn't do a good job and triggers a code... I believe it's because the heater circuit has no load). Maybe I can turn this off in the original ECU's tune).

Are you using the OEM crank sensor? I think I may have worked it out at one point... Is it an AC signal with 5V max? https://youtu.be/drh8Ebhobg8

And yes, anything you wan to share would be greatly appreciated (crank sensor angle, fuel tables, etc.). I am hoping that autotune can do the heavy lifting, but getting something close to start with would be greatly appreciated.

These throttle bodies might work for you, and have a TPS built in: https://ecotrons.com/small_engine_fuel_injection_kit/

Here's the thread I started a loooong time ago with more photos of the throttle body Microsquirt ECU long-term slow project

Ohh, yeah mine might actually do you pretty decently with all of that done. You're not the same as my build but you're pretty close.

I looked at that throttle body, and its too small for the GTS engine, the GTS is a 32mm TB, and that one is a 28mm. The GTSs throttle body is already kinda restrictive, that would just be worse... I'm thinking of swapping to one from a 04 Suzuki GSX-R as it has 38mm TBs that can be broken up into individuals from the rack of 4. But thats down the road for now. The stock one is working...

I am using the OEM crank sensor, its a VR type sensor (So yes, AC at 5v), with a 24-2 trigger wheel(22 teeth, 2 missing). The sensor angle is 635 degrees BTDC. I opted to not use the stock coil as it would have needed resistor packs, instead I took a single coil-near-plug coil from a corvette(And other performance LS motor cars) as its a logic level coil that needs no resistor packs, works wonderfully with the Microsquirt, and has a MASSIVE spark output which is nice.

The Microsquirt supports CANBUS, which if I recall is how the dashboard talks to the stock ECU, so it should be possible to get the Microsquirt to talk to the dash... This might be a LOT of work though trying to decode dash address space. But it'd be pretty tricky if you did. You could repurpose the gages to do ANYTHING you wanted.

You CAN turn the O2 off in the original ECU, I borrowed a friends tools to dump the stock ECU because I wanted to take a look at the timing and fuel tables to be sure I was in the correct ballpark for mine when I started tuning and saw the option for it.

Autotune can absolutely do the heavy lifting if you have a good base map, with what you've built I'd bet you'd start up fine and even run pretty decently with my tune, then autotune would get you the last little bit there.

Ecotrons actually has a wide range of throttle bodies (28mm, 34mm, 38mm, 45mm...) but I like your idea of reusing an OEM part from something else... probably better quality and lower cost.

What tool were you using to dump the stock ECU? I've been using GuzziDiag with Tunerpro, but had to manually modify the 300's XDF file with a hex editor just to get some values to read on a 250 (really a MIU1HW201 vs. MIU1HW101 hardware issue, not 300 vs. 250). Unfortunately I haven't found the hex address for the lambda flag yet... any idea how to track it down? Related thread: DIY Diagnostic tool for injection Vespa's with MIU ECU (Page 3)

One more thing: how should I address the OEM throttle body IAC? I won't have any control over it, but it will still be active... I've considered fabricating a fake value for the coolant temp sensor, so that the OEM ECU thinks the motor is already at operating temperature and at a consistent value (my theory is that the IAC would remain constant).

I may have already decoded something that controls the IAC table... but the naming schemes in the XDF aren't really as obvious as they could have been.

Ohh awesome, I didn't realize that. The only one I had spotted is the 28mm. I'll have to take another look at them.

I had a friend dump his GTS with GuzziDiag and send me the BIN which I used in Tunerpro with an XDF I found on a tuner forum somewhere. Let me see if I have the lambda flag on my XDF, I think I have it.

I totally disabled the stock IAC, I actually pulled the whole ECU board out of my throttle body as I was hoping I could repurpose the stock TPS, sadly its a wiper directly on the ECU board so I couldn't. HOWEVER the IAC pins are detachable from the ECU board and it seems to be a fairly standard 4 pin stepper IAC from testing which I should be able to repurpose the stock IAC with the Microsquirt, but I've not yet tried to... Because of this I'm idling a LITTLE high. Its not enough that I'm gonna do anything about it yet, but I'll address that down the road.

Try this XDF out, its for the MIUG4 ECU's in the 300HPE but it has the values to disable the lambda sensor.

MIUG4.zip
Description:		Download
Filename:	MIUG4.zip
Filesize:	5.98 KB

I was browsing another ModernVespa thread looking for something else, and came across a MUCH better XDF. That one has the Lambda sensor flag already mapped for the MIU1!

Its in this thread: DIY Diagnostic tool for injection Vespa's with MIU ECU (Page 3)

There is more than one version of the MIU1 ECU, which can be identified by the hardware version (MIU1HW101, MIU1HW201, possibly others). I believe all 250s are HW101, and all 300s are HW201 (unless of course it has a MIU3 or newer ECU).

I made that XDF file in the other thread from a modified 300 XDF (HW201), but I was never able to figure out the correct hex values for the HW101 lambda. The toggle still exists in the XDF, but I doubt it does anything at all since the ECU isn't looking at that specific address for the lambda control (there's quite a bit of empty space in the BIN file). FWIW: just about every HW101 table has a different hex address than HW201.

This shows the hexadecimal addresses that I was able to get mapped, and what I am still missing.

Ohh, lol. I'm a dummy. It completely slipped past me that it was in fact *YOU* who posted that in the first place... Carry on... Nothing to see here

No worries.

I haven't checked the tables, but do you think it's possible to translate fueling from tunerstudio to tunerpro? (from Megasquirt to OEM ECU)

Hmmmm, FROM the Megasquirt to the OEM?? MAAAYYYBBBEEE? The biggest problem (at least with my tables) is I'm currently using the Megasquirt AFR target maps. So they're not direct 1:1 fuel output but the result of some math telling the ECU how to calculate the needed fuel from the AFR, where the stock ECU is going the OTHER way. It has a base fuel map then uses the O2 sensor to modify that map... That being said I feel like it should be possible. Are you thinking of trying to push my Megasquirt tune to a stock ECU?

Yeah, get it running and tuned with Megasquirt, then convert the tune back to stock ECU format. Running the Megasquirt as a piggyback isn't really optimal for me, even if it is better at tuning. I would rather everything work off of an original ECU for dashboard compatibility issues, simplicity, weight, etc.

Plus it would allow me to use the Megasquirt for another project I have and allow for me to share my tune with other people who don't have the Megasquirt.

For sure, makes a lot of sense. Let me noodle on that for a bit. There'll be some conversion needed for sure but I don't see why it couldn't be made to work. At the end of the day a fuel map is a fuel map...

Looking at the GTS dump I have, do you know what measurement the fuel tables are using? They go up to huge numbers (4500+) at WOT, where my table is based on Volumetric Efficiency so my numbers top out around 105 right now.

Possibly microseconds for the injection pulse? I'm guessing from what I learned here: https://wildguzzi.com/forum/index.php?topic=73938.60#:~:text=First%20up%2C%20the,map%20are%20microseconds.

Thats sorta what I expected, thats what a lot of ECUs use. That seems like it makes sense looking at the stock fuel map. Now I just have to noodle out how to make that work vs a VE table.

I think there's some multipliers I'm not understanding in here, as the times don't quite seem to make sense. If I'm doing the math right at idle the GTS ECU should be running on an injector pulsewidth of 1.657ms which seems REALLY low. Most engines are about 2.5-3.5ms.
I'm idling on my Megasquirt around 5.9ms. Which is probably a little high as my idle is a bit high but thats quite a difference in fuelling. I'm going to have to wrap my head around how the modification tables affect the base fuel.

I'm not sure what fuel pressure you're running, but the 250 (and 300?) have a 2.5 bar system. I could see how a lower fuel pressure would result in a much longer pulse width.

Also I'm not sure if converting to a different pressure is linear... as in would a 158 cc/min injector be 131.67 cc/min @ 2.5 bar?

Some info I've been collecting on the fuel injector options:

Answering my own question: it's not linear [Advertised Flow Rate] X [The Square Root of (Your Pressure ÷ Rated Pressure)]

https://help.summitracing.com/app/answers/detail/a_id/5223/~/how-do-i-fine-tune-my-fuel-injector-flow-rate%3F

Updated table with 2.5 bar calculations:

More fun calculations. Going off of this guide: https://www.team-integra.net/threads/calculating-injector-pulse-width.46738/

The 250 @ 9500 RPM & 100% VE should take 3.42899 lb./min of air (45.11829 CFM). To achieve a 14.7:1 AFR, 0.233265 lb./min. of fuel would be required. The stock injector (144.2cc/min) will only flow 0.228889 lb./min., assuming 100% duty cycle.

It looks like the stock injector might be undersized on the 250.

Ohh, it just occurred to me that I'm also not making my table for 14.7AFR, I'm between 12.8 and 13.5 as the performance is much better there which is likely part of it as well.

I'm running at 46PSI which is 3.17 BAR as I discovered that the injector is indeed undersized for the GTS at it's normal pressure rate. The IWP182 injector is rated for 158cc/min at 3 bar but is good up until 6 bar so there's lots of room to get more fuel from it. At 3.17 bar its flowing 162 cc/min.

I love your Buddy, Kaos! I remember your machinations some years ago at Modern Buddy. Glad to see it live again, in any form.

Hey Syd, long time! I posted this over at MB too, but it seems to be a bit of a ghost town these days sadly.

Thought I'd give you some updates on viable injectors from your list there since I've tried several now.

The IWP069 injector will NOT work on a GTS. Its a 'pencil' pattern injector thats spray pattern is not fan shaped. The IWP063 is a much better choice, it flows 383cc/min at 2.5BAR. The IWP043 is another good choice and flows 300cc/min at 2.5BAR.

Its been a little bit since I've updated this thread, so I figured you all might like to see some new developments...


That complicated conglomeration of hoses and tubes is an IHI RHB31 turbocharger! Yup. The Buddy is now turbocharged!!

I've also taken advantage of my Megasquirt's flex fuel ability, and added an E85 sensor. Running on E85 its capable of putting down 25PSI of boost, which using some back of the napkin math says the engine is putting down somewhere near to 60HP. Its an absolute MONSTER and has gone off the charts on the over-engineered build charts

you beat be to it. wish i could ride it. before you blow it up.

Well, to be honest I've blown it up once already...

I tried 25PSI on pump gas and blew the ring lands outa the piston. Now I keep it down to 12PSI when I'm on pump gas, and try not to run anything less than E30 at any point. The Ethanol cools the charge down and has a lot higher octane rating than normal gas so I can run more boost without problems on it.

If you're ever near Portland, come take a spin. Just fair warning, it'll try it's hardest to kill ya! At full boost its hard to keep the front end down even with the 8 inch stretch and all 200lbs of me leaning on the bars. It just GOES.

many have dropped properly designed and tuned turbo setups on 10/1 NA engines. 12psi is too much

I swapped to a forged piston, and gapped my rings wider and so far with a set of det-cans I'm not getting any detonation or heat spikes so its holding up fine so far. The GTS has a surprisingly stout bottom end, as long as I can keep detonation under control. And with the Megasquirt I have a LOT more sensors to keep all that under control, as well as ability to pull timing on the fly if detonation happens.

I've got about 200 miles on it like this so far, without issues so its doing fine at this point.