Modern Vespa

Hello,
I'm Andrea from Italy, my Vespa is a '81 P200E.
Searched for solve a problem on my carburetor (still not solved) I come across in this forum.
Very interesting topics threaded, thanks to all 🍻

ciao. where in italia are you? not many vintage bikes there. what is going on with your carb?

buongiorno! I'm hoping to be in Napoli to see McTominay & Krava play footie this Spring!

I'm from Turin, in north west of Italy. Correct, a lot of vintage bikes have been scrapped for anti-pollution incentives over the years, many others have been sold abroad due to lack of interest… but not all of us are like that, fortunately
Coming to the carb problem, in short, I fitted last spring Malossi Sport in C60, carburetor Pinasco SI26ER with bell (all tips to increase the flow rate had been done) and Polini original box exhaust. The engine had a problem with clutch side Malossi seal, but now with Corteco there is no more air leaking, tested pressurizing the crankcase.
Well, changing many main jets, atomizer, min jets, related air correctors and slides I got a pretty good behavior, but at high revs and slide at 1/4 (80/90kmh~) it is always lean, whatever I change, it stays lean.
In WOT egt stay around 640/650c (1200F~), but if I decrease the slide at 1/4~ the egt raise fastly to 700c (1300F~) and I can feel it lean, and after a few seconds I am forced to let go of the accelerator.

If for you it's better I could create a dedicated thread to deep in details.

Welcome, it sounds like you know these things, and what needs fixing. Instead of a new thread, you can go to your first post in this thread and hit the 'edit' button, then add ,'carb help needed' after your clever flag. I'll bet Jack and Chandler* will see and come to see what's up. Please post up a pic of your scoot as you wait, we love pics here!

* Usually know what to do and other ppl who do will show up too.

PS: how did you put your flag in your post title?

If you are posting from your phone (Iphone for me) you just use the emoticons available from the iOS. Same way you'd add one to a text message.

Oh and Welcome Andrea!

Thanks so much! Yes as already said by V oodoo I created thread with my phone using emoticon in the title.
I am going to insert some photo, a couple decent at least 😅
Yes, I detected the problem but I didn't manage to solve it, after a lot of research and above all try (almost every morning from April going to work I tried a different configuration) I decided to write here where I found the most knowledge over the net.
The problem almost seems like in that condition the vacum is not enough to
suck petrol neither from the maximum pipe (which is located on the opposite side of the slide opening) nor from the minimum hose.
Is it possible to get around the problem?

Here we are, this is my Vespa some years ago, now is a little more lived
I know, the colors, emblema, and so on are not original, but I restored it in the way I liked, I would have left it a little rusty, but trust me, it was in a too bad condition.
With the previous engine, a 208 Polini I fitted 30 PHBH carb with JL right hand exhaust, but unfortunately I don't have any photos.
I come back to SI carb both to keep mix and for challenge (so far, SI carb is winning vs me 😅)

Welcome.
What jets do you currently have in there?
What jets have you tried?

Am watching this thread - have one of the same issues as the OP, lean running at below 1/4 throttle at speed, no matter what I do with the idle jet.

My latest hunch is that the idle circuit's clogged up somewhere, and my carb cleaner & compressed air treatment isn't cutting the mustard. Am looking for somebody nearby with an ultrasonic cleaner.

Thank you so much!
Now for trying the current configuration is 120AC-BE4-150 , 110-60 and slide 4.

During my tests (ordered here from leaner to richer) AC passes from 190 to 120, atomizer BE2, BE3, BE5, BE4, main jet from 145 to 160, AC min from 160 to 100, min jet from 55 to 100 (yes, 100-100, I wanted to understand when idle jet stops to work, and in my engine do it at 5000/5500rpm) and slides 4, 5, SIP 4.2.
Slide without clip makes the afr richer at 1/4-1/2 throttle opening and low rpm, after 4500/5000 I think the air passes only through the main duct. For this reason I come back to slide 4, because 4.2 and 5 make afr richer where it was not necessary, at high rpm and 1/4 throttle.

I started thinking that when the throttle is quite closed the air in the main duct does not pass forcefully near the main jet pipe and the vacuum is not enough to extract enough petrol from there. Min jet stops to work at high rpm, maybe when the speed of the inlet air is high and has difficulty getting petrol out of the min hole, because of its position.
But these are my assumptions, probably wrong and maybe it is possible to be solved

Idle circuit is void if throttle is cracked.

Since you've tried EVERYTHING, I'd shelve the venturi and re-jet with a stock/Cosa/no filter.

Actually I don't know if I tried everything, maybe I am losing some modifications to be done that I hadn't thought of, any tricks or changes that I could still do, for this reason I ask for help from those who know more.
Btw I already tried without Venturi, the only difference I found was a smoother behavior at low rpm with it.

Do you have the plastic tray under the tank installed?

Other wild guesses:
You're jetting a carb/box gasket air leak.

That venturi has the air correctors exposed to the air stream, right?
Some on the GSF experience a lean as you describe, which seems to be counter-intuitive(?) offhand. It may be a thing others without dyno's, EGT's and AFR's don't see and try to jet to compensate.

Have you tried riding with a filter?

If you're set on a venturi, the Vesptec and Auer venturi's and their big airbox covers are better. They're printed plastic, though.
The VMC venturi is aluminum, and has a kind of heart above the jets that isolates the air correctors from the stream of air. I'm sure they didn't design it that way without a lot of trial and error.

Quite striking that yes.
When you look at the relative ´hights´ in the carb, air flow there is a logic behind it imo.
The jet stacks take in air above the bell mouth, they empty in the real venturi in the carb.
Since the flow of emulsion/mixture through the main tower / pilot circuit is ´driven´ by difference in air pressure, shielding the air intake of the stacks from the flow will imo both increase and stabilise the difference.

Yes, it is correctly installed I had problem with clutch seal but actually I did air leaking test without carb box, but gaskets are correctly pressed. I have also removed rubber gasket between carb and box to have no further doubts Yes, the Venturi has air correctors exposed to the air stream, does it worth a try with another Venturi? Yes, with a T5 lowered (I did it 15 years ago when it was not simple to find a big box cover), but it has more torque at low rpm, but a lot of power less, so I removed it I could try with a plastic one (I don't like the VMC esthetically and also it is a lot expensive), maybe something will change, thanks for suggesting!

If I can give you any other clues, the engine runs good, but it stops to rev at 7800/8000 rpm, it seems to have a mechanical rev limiter, it's impossible to rev more.
Also under 4000rpm it hasn't much torque.
I have original ignition with PX200 elestart flywheel, maybe is it because of timing on cylinder (178-122) and crankshaft (120-71)? Really strange. The front wheel rarely floated in acceleration under that engine speed

Another clue is that the best ignition advance is more or less 16btdc, for torque and CHT, if I increase it no more torque is provided to low rpm, strange isn't it?
Compression ratio is 11:1 and squish 0,9/1mm

Can you elaborate?
It's very easy to warp a Spaco carb

Yeah, very strange.
Does RPM increase at idle when it's at operating temperature?

I always love to see the fountain above the carburetor, air an fuel mixting

hence foam filters potentially soaking and complicating carburation.

darn, I only opened the post because I thought you had a big plate of pasta you needed help finishing

I mean that I removed the round rubber gasket (o-ring like) positioned between carb and carb box, because when I screwed the carb it was really hard, maybe the rubber gasket was too high or carb too low.
sorry but it's difficult for me to explain some things

How can I find out if there are air leaks between the carb and the carb box?
This would explain the low torque below 4000 rpm, right?
Sometimes it seems to have a lot of torque when cold, just turned on, but after a few meters it loses it. Maybe it's just an impression yes, not so much but I think more ore less 200rpm higher at operating temperature, I have to pay attention to it unfortunately not, that would have been much more satisfying
bit if anyone happens to be around here it would be nice to eat a plate of spaghetti together

Just to start with the easier things to rule out, I'd get a sheet of 400 grit sandpaper and place it over a flat surface, like a thick piece of glass, and do a few figure 8's over it against the base of the carb. If it's warped the score marks will show it.

Do you see a lot of blowback when you rev it with the cover off?
May provide another clue.

You're current jetting is super rich for that setup

The mixture screw tapers off very quickly at barely open throttle, but it doesn't just shut off. Have you tried adjusting it after every jet change?
That's a must.
BGM makes a mixture screw that can be marked and adjusted from inside the carb.

https://www.scootermercato.com/Scooter-Parts/Carb-Parts/BGM7305

I'm late to the game because I've been either sick or working on my own bikes, but I'll try and make up for lost time.

So just to confirm your setup...you're running a Malossi 210 Sport w/ a 60mm crank, Polini box, and 26/26 carb.

The Polini box is limiting your higher end RPM's. That's a known issue with the exhaust. It does good things on the ramp to peak power, but falls off faster than a Malossi, SR3, or any of the BigBox'es. Get a different box if you want power out past 7,500 RPM's or so.

You say your EGT shows hot/lean at 1/4 throttle (50-55 MPH in 4th, I assume). That's only about 5,000 RPM's. That's enough power the motor isn't just lugging at that point. That takes me back to an air leak again.

Assuming it's not an air leak, Ray8 has some great experience with tuning 1/4 throttle on the SI's and he likes the Lemarxon atomizers (get 'em from SIP, search on here for his posts on the topic) for more/better adjustment there.

First thing I'd do if I were you is get rid of the venturi. It's mostly effective in the 1/4-1/2 throttle range, but the rotary valve is the constraint past 1/2 throttle, so it's doing you no good up top and hurting you down low.

Speaking of the rotary...on the intake, what have you done to extend width or intake timing? Are the transfers ports matched?

Fundamentally, you're probably running too large a carb and need to just go back to a 24/24. The motor doesn't draw enough air through it to generate adequate vacuum, which tends to manifest from off-idle up past 1/4 to even 1/2 throttle. It's the nature of the SI. And physics. There's a reason that no modern carb looks like an SI.

Now getting back to your specific symptoms, I agree with Ray that a lot of what you're experiencing sounds like a combination of jetting around an air leak and too much carb.

(when you said you "removed the rubber," do you mean that you removed the gasket under the carb? If so, put that back. You're going to be leaking air.) .

So in closing, if I were you here's what I'd do:
1) re-test for air leaks. Do a proper pressure test and make sure it passes.
2) Get rid of the venturi. It's only hurting you.
3) If you're still having problems, get a 24/24 carb. Set up the main stack 140/BE5/130-135 and see what that does for you.

And welcome to MV!

I forgot to ask in my last post, but what are your port timings, squish, and ignition timing?

I skipped them because they probably are not relevant to your core jetting issues, but might be handy to know as the troubleshooting evolves.

the carb is new, only 2-3kkm, I modified the tap it and I have never screwed it in more than ~1.3kgm.
Btw, I will try with sandpaper the same! I've never take a look at blowback while rev it, on the airbox cover there is some fuel sprayed. I will do this test actually I adjusted once when I changed idle jet. What should I do differently?
I already cut the mixture screw to stay inside the box, is it different? Thank you very much for your intervention, I have read your guide on SI many times My setup is
- Malossi carter
- Malossi Sport cylinder 178-122 kit with exhaust to 62% and piston modified sideways. RC 11:1 and squish 0.9mm
- Tameni crankshaft 120-71
- carb SI26ER with Venturi and airbox polini
- Polini Original exhaust box
- gearbox 125 Arcobaleno with 4th z36
- primary 23-62 BGM
- New Fren clutch with 4 Malossi springs
- 200 Elestart flywheel without ring for starter motor

Yes, I used Polini box for have torque at low rev, but actually in my case the torque is limited to 4000 to 7500 rpm, under 4000 seems a 125cc (compared with my old Polini 208), maybe it is normal for this cylinder, I have never tested another healty one Correct, EGT shows hot/lean from 1/4 to 1/2 throttle (according to the marks on throttle grip), my gauge indicates 60 MPH in 4th at 6000 RPMs I already know them and also his slides, but before changing further atomizers I would like to understand if there is actually a problem with my engine, am I wrong? actually the only improvement i heard is getting low revs smoother, I will try to remove it and test again I extended both valve in the carter (not much, the area is calculated to use a 28mm carb) and removed material from the crankshaft. Edges and steps are removed, from venturi to exhaust I already tested with my old 24/24 (with all the work in the ducts, main jet and tap), but the result is almost the same, maybe it gives a little torque more and less revs, but not much no no, not the paper gasket, the square o-ring (see the attachment) I will do these advice for sure! Thanks a lot ignition timing is more or less 16 btdc, for torque and CHT, if I increase it no more torque is provided to low rpm, the better result I obtained for torque and temp is 18 btdc and Kytronik, but I removed it so as not to put too many variables
in the meantime I'm creating an additional module to use with the original CDI. It is programmable at runtime from a console. But now I don't want to bore you with this thing, it already works but it's still in its infancy, my projects always go slowly due to lack of free time, if it can be of interest maybe I'll open a specific thread

I usually don't take many pictures, I'll attach some of the engine

When tuning out of spec engines, using stock parameters as a base is a good foundation. IE ignition timing and sparkle plug bone stock. When everything else, is accounted for (carburetor adjustments and breaking in the engine so the rest can be dialed in)
When it runs safely down the road, meaning not scattering and rider safety. Then you can (after) fine tune for more max power from your new plant.
Once you know the specs of a given engine, this process goes faster.
Gotta make the rings and everything else top notch broken in, or you're a cat chasing its tail.

The workmanship on there looks really nice

I've been playing with my port timing calculator and can't get a setup for the Malossi 210 measurements I have that gives me 122TD/178ED. (Plus, my spreadsheet isn't really setup to work this particular scenario)

If someone else has port heights for a Malossi 210 sport they can share here to confirm, that would help a lot.

So is 122TD/178ED measured or off the spec sheet? That's pretty low for a properly set up Malossi, and a little bit low for the Polini box, even. Rule of thumb is that 122 TD is going to get you peak power at about 7,000 RPM's, which matches your description (and the Polini box, more or less).

Given that the TD and ED don't match up for my unmolested Malossi 210, I'm curious to get to the root cause of that. :?

Again, let me know what you have for base and head gaskets and confirm those port timings.

So on the top end, you may never get much more than like 7K-7,500 RPM's with those port timings, so you'll just have to live with that until you can get a base gasket on there and maybe a different exhaust.

Also, your squish..0.9mm for squish is a little aggressive, especially if you're having heat issues, just in general. I'd try to get it up to at least 1.2, but not more than 1.5. That'll help with the heat.

Now, let's get back to the carb...

So for now, I still think you should remove the venturi and add a base spacer. If your port timings really are 122/178, then your blowdown is only 27 degrees, which may be preventing adequate exhaust flow, which again could keep heat from exiting the motor effectively.

I still think the 26/26 is too big, and that you're super-rich on the top end. You can't get a good read on it because you don't have the port timings for it to properly rev so you can tell if it's revving cleanly or not, so don't worry too much about it for now.

Here is the port map for my new Malossi 210 Sport.

Main Transfer height: 45mm
Center boost Transfer height: 46mm
Exhaust port height: 32mm
Exhaust port width: 40mm (58% of 68.5 bore)

feel free to ignore the other written stats , I'm still working things out for my build.

Thanks, Jesse!

Those numbers work for the timings, but only if I put in a deck height that doesn't really make sense. (2.7mm piston ABOVE deck) I'm going to just ignore that for now. I'm wondering if that's somehow related to the whole 210/221 thing Malossi does, as if anyone building a long stroke 200 should be trusting others to set their port timings for them.

That also confirms installing a 0.5mm base gasket. That would get the timings up to 125/180, which is a lot healthier, and also get the squish up to 1.4mm, which is going to do better for heat management.

Then we can start to worry about the carb.

This is getting me motivated to go get my 210 back into fighting shape, even though the GL is still not officially good-to-go.

Happy to help. I'm following curiously, as I'm working on figuring out and setting the port timing & squish for my 210. Although my fuel delivery set up is different, cylinder is the same.

I'm shooting for a 1.2-1.4mm squish, probably towards 1.4; as this will also push the port timing up just a tad bit more.

thanks, as usual when I take care of engines they always give me problems, otherwise they always go... like wom... ehm I am joking of course
sure, I can give you all configuration I tested, consider that upper shape of the TD and ED are not touched, the only do I did is to modify exhaust hole laterally (62%) and bottom to adapt it to C60.
Also the base of the carter or the way you measure it may vary results
the current configuration is:
122 (~121) - 178 with 0,3mm base gasket and 1,5mm gasket to the head

other tested configurations are
126 - 182 with 0,15 + 0,2 + 1 mm base gasket
128 - 184 with 0,3 + 0,5 + 1 mm base gasket

the results are pretty the same, it just only shift max torque peak. But 128 - 184 configuration was the funniest actually, but the torque riding with passenger was not enough and I had always to play with gears.
I tested also a Polini head (I like it) and the engine was more nervous (squish angle is different) but this head has a big problem with temperature, you have to modify a lot its cooling fins or the cylinder cowling, for that reason I put it back on the shelf

let me give my 2 cents on squish topic, in past I did a lot of experiments on that and the result has always been the same, keeping the squish as low as possible considering thermal expansion and any assembly tolerances
This ensures lower temperatures and a much lower risk of knock (which instead proliferates if kept high). Above 1.4mm it is not more squish, it is just distance between piston and head
Temperatures depend a lot on compression ratio, not on squish itself. But I tried with the second configuration to keep it to 1.2~1.3mm and it confirmed my theory.
Having said that I don't want to say that it is always like this, but this is only to share what I have learned in my tests

Regarding the carb I could test again with my old 24/24 without venturi and compare results
Thanks to all for sharing data

My exact measure on your timing was 121.8 TD. I still think you need another 0.5mm of base gasket. You want to be about 124-125(max) TD and not worry about ED. You will have plenty of blowdown with the widened exhaust, regardless of the measure. No surprises here. 126 is too high for that box (really, most boxes) and 128 is definitely tuned pipe territory--if you want peaky, get a peaky pipe. No surprises here, again. I built a series of motors with BGM177's that had squish in the 0.8mm range and they always struggled with heat when I used them for touring. They were great for raw power and acceleration, but tended to get hot like yours when running on the highway for more than a couple miles.

They were reeded with big PWK's, so not a like-for-like, but similar challenges.

Recently, because the build docs called for 1.2-1.5mmm squish, I decided to change it up and have now built two ~30HP motors (Quattrini TV210 lambretta & Vespa M1XL) that both run with 1.4mm of squish and stay really cool, even running uphill at 65 MPH, so maybe trust me on this one

(It also puts your port timings where they should want to be) 100% agree on this

I can't do much with bowl size on the head because I don't have access to a good machine shop here. Truthfully, though, I've never built a motor where I really needed it, so I don't consider it to be a problem. For some reason, the Malossi 210 seems to be the Mount Everest of tuning. For instance, take a look at sdjohn's P200E build thread. 42 pages of effort and he never REALLY got there. Like I've been saying, I think your best bet for now is a .5mm base gasket and ditching the Venturi. Then you can get back to the carb with a setup that's much more in line with expectations as a baseline.

We've never discussed what your tuning goals are. I just assumed you want a fast touring or city bike since you're running a box and mentioned riding two-up.

If that's the case, you should consider accepting a slightly de-tuned, but more usable build as the eventual outcome. So long as you're on rotary intake and an SI carb, you're always going to be challenged to really build a winning motor. Same with the Polini box.

You will have to get some reeds, a better exhaust, and a proper (side draft) carb that has significantly better tunability if you really want to max things out.

sure, I could do it both adding and a 0.5mm base gasket and keeping 1.5mm head gasket (actually there are 2 gaskets 1 + 0.5mm) or adding 0.5mm base gasket and removing the 0.5mm head gasket
but I don't have great expectations, I think it will be in the middle to the current configuration- and the 128 - 184 one. Compared to others, this engine does not change much with the various setups, I also see this with the ignition timing, the changes are really minimal from 23 to 16 btdc
btw I will do that to have a more correct cylinder timing I still have JL right hand I used with Polini 208 and 30 PHBH carb, I already tested it and with this engine it doesn't rev more than 7500rpm, Polini box is much better with this setup. Maybe this engine has a problem somewhere. I will do the air leakage test again and check gaskets under the carb
I could have for testing Malossi box too, but from what I know it shifts the torque even further to high revs Yes definitely it worth a try on 1.4mm squish, actually I've never managed to test this engine for miles at mid throttle without high temperature problem so I didn't test it also in full throttle. I completely agree with you, when i decided to treat myself to the new engine i read a lot about the cylinders available on the market in 2023 and the choice fell indisputably on the Malossi Sport in C60, because according to almost everyone I read it is the cylinder that makes the vespa a rocket. Now i don't know what kind of rockets everyone is used to, but honestly I am very disappointed. I really hope that my engine has some problems, so maybe i will have a chance to change my opinion I tested small AC with big MJ and this engine swallows everything, I am going to try your suggested configuration 24-24 with 140-BE5-130/135 and without venturi my challenge was to create an engine with a box and SI carb (initially I thought to fit the SI 28 Pinasco, but I didn't want to modify it to keep the mixer. What rotary intake engine will be right with this carb?) with as much torque and power as possible to use Vespa every day and sometime with a passenger for travelling keeping "high" speeds...

Hi all,
thanks to your advices I checked my engine and the carb, especially without gasket, was swinging in the box (the gap was more ore less 0,15mm).
I bought the carb box on eBay because only one I had for spare was enlarged for PHBH 30 (test for keep mixer) and probably previous owner did some experiment or had screwed it very hard. I had noticed that the was moved, but I didn't give it much weight because I thought it was the rubber gasket that after I had removed.
I built a tool to smooth the box surface that was not on plan and now the carb doesn't move anymore.

I've just tested Vespa, for sure it has more torque at low rpm, more nervous. At high rev and full throttle didn't change, but I think it's normal.
The strangeness is that I can take high rpm also with very rich configuration in first and second gear too! Is that normal?
For understand what changes I set it leaner with 140AC-be5-150, it seems to be better but I didn't try at high rev and 1/4-1/2 of throttle, it's really too cold outside, will try to do that test this weekend.
I will try also with 24-24 without Venturi and to add a 0,5mm gasket under the cylinder.

Again, thank you all a lot for putting me on the right path and making me think
if one day I have the pleasure of meeting you, I'll pay for the beer at least 🍻

Andrea the planning looks great can you show us the tool and how you did it?