Modern Vespa

Nice work!! Glad to hear you are making progress.

Please, don't change port timings and switch to the 24 carb at the same time
The Pinasco 26 "should" work well with this setup.
What jets do you have to try?

Btw the BE3 would be a better baseline atomizer to start with.
And if you have pilot jets in the 58-68/160 range, also better.

The mixture screw has to be adjusted after any jetting change!
The BGM has a better taper than the Spaco, and it's easier to rotate from inside the carb for you guys that have e-start. It isn't necessary.

And another btw:
I'm terribly jealous that you have an egt, afr, live in Italy, and don't have to eat leftover turkey for the next five days

Hi hibbert
the tool is actually very simple, I left it in the garage where I do the work, it is 2 pieces of iron slightly larger than the base of the carburetor.
one of these flattened well on one side and created 2 threaded holes to keep the second piece of iron attached. This second piece has the holes in the same position as the first one, but slightly larger to allow them to be screwed together.
then it was enough to pinch some well-stretched 600 sandpaper between the 2 pieces of iron and pass it over the surface.
If you need it I'll make a drawing, but it's really simple yes, thanks to you all Actually I didn't try a lot, because of cold weather, I have the BGM MJ set and AC set too. Don't have much pilot jets but I could create them. I have a 100-60 (created from a 55-160) and the 160-60 took from Pinasco 26 Ok, will also try starting from there, 140AC or better 120? is there some procedure to understand if screw is correctly set for each jetting change?
No I don't have the starter motor, my Vespa is older than elestart version. It's electrical system is without battery. I cut the idle screw to stay inside the carb box, but I regret it now that I know that it has to be rotated at every jet change..
don't be jealous, I speak your language very badly, aren't you in USA?
egt reader is done by me with an Arduino, a display and a few components more, if you saw it you would start laughing
Once the temperature problems will be solved (if it will be), I think I will remove it also because the cable passes on the footboard and reaches the gauge held with a piece of inner tube on the drawer under the steering, my colleagues who arrive on brand new, shiny scooters look at me like an alien on a old Vespa

It looks like you're making some progress.

I'm going to guess that you're still too rich on the main jet, but doing better than you were. What happens is that you will be able to rev out when the motor is not under heavy load (like on the stand, or in low gear), but once it actually hits resistance, it's not producing enough power to overcome air resistance or gravity if going uphill and bogs out.

I just worked through this same issue with my GL, and it's still not dialed in, but it's also getting better.

I hope it is the right way, for sure the behavior at low rev is better
Today I tested 140AC-be3-160 and 160-60 (I would for testing to put back the 100-60 but I forget small screw driver at home) and it can rev it in first and second gear without hesitation, it doesn't seem to be rich, but the problem at high revs and 1/4-1/2 throttle is still present. Have I to come back to 120AC-be4-xx and 100-60?
For feel differences in jetting I kept 26 Pinasco with Venturi
What is happening with your GL?

You have a 160 Main? I'm surprised that will rev out at all

My GL is a VERY different problem...PWK34 on a direct intake Quattrini, but I did have the main way too rich for a bit, which caused issues with revving under load.

You can pick up the thread here if you want to keep up on the current build.

"I'd" do two things.

Confirm the channel to the main jet from the fuel bowl is fully drilled.
Remove the main jet stack, shine a flashlight down into it, and check that the hole is drilled all the way through. This isn't an uncommon thing with reworked Spaco's.
This can probably be done with a cheap endoscope, which is a great tool to have around, btw.
Avoids having to remove the carb... again.
https://www.amazon.com/gp/product/B07C9C6P5D/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

If you want to continue with that venturi, a larger set of pilot jets "should" help 1/4 throttle.
Read the description:
https://www.scooter-center.com/en/idle-jet-set-bgm-pro-dellorto-type-9892-si-58-60-62-65-68/160-bgm857kt

"Ringing" = lean condition

What does ringing sound like? I've heard the term but not sure what it means.

Sometimes ringing is just ringing... that's why they added rubber blocks between the cylinder head fins - to absorb the 'ringing' of the fins. Other vintage two strokes have rubber blocks between cylinder and head fins to reduce ringing sound that vibrating fins make.

In my experience lean pre-ignition which leads to detonation sounds like weird static crackling - which can lead to fins ringing, which sounds like the engine is shaking a can of marbles. Or it could be just fins ringing, which is why they added rubber blocks later on...

Yes, it seems really strange, it can revs 160mj also with a 120AC and smaller.
What a cool project, I want to read all your thread, thanks for sharing The channel to the main jet from the fuel bowl is drilled to 2,5mm and it I just checked again with drill and it was clean
I already bought the oscilloscope to check from the spark plug hole if engines are seized before to remove cylinder head, and a lot of time I didn't have luck is it correct to keep 160AC for pilot stack? during increasing vacuum doesn't getting lean? in my engine with 160/60 for example I can hear strange knock sound, even it is not under load and low rev, with 100/60 I didn't heard it... maybe it's pure coincidence. Under load I didn't heard knocking noise

PS: today I tested 24-24 Dellorto without Venturi, channel to the main jet from the fuel bowl drilled to 2,5mm and performance are less than the 26 with Venturi.
24-24 with 140AC-be3-160mj 160-60 and it was rich, when I tried to rev it in second gear it sputtered. Instead with only changing mj to 150 it worked better, but I don't like it, torque is less (also at low rpm). Ok, maybe it is not perfectly jetted but 26 with Venturi in all configurations of my engine goes faster. Is it strange?

I've seen many more similar-to-yours setups with this pilot range vs otherwise.
The larger fuel size is key here with a venturi.
Pretty sure this is why Pinasco first came out with this range(?).

If high temps at 1/4 throttle is your only current issue, "I'd" try this.
Not a big investment.
The main stack is not a factor here, aside from all fuel to the pilot jet flowing through the main jet. MJ stack initiates at around 1/3 throttle, influence depending on the AC and atomizer.

Like the MJ, start with a bigger fuel size and go down until you can accelerate smoothly from a rolling stop in 2nd uphill (load likes rich) by adjusting the mixture screw from 1-5 turns out.
You can fine tune this later.

Pilot jets ordered, the problem, according to the notches on the throttle grip, is between 1/4 and 1/2. So maybe also the main AC Actually I already tested with 120AC-be4-160 and at full throttle it can rev without hesitations. Have I to find bigger jets?

Today i did leaking test and after 5mins at 220mmhg it didn't lose any pressure. Did also vacuum test and did the same. I also tried to push on kickstarter slowly and the pressure after some oscillation come back at the same value

my thoughts exactly. flattening the bottom of the box = easy, but he somehow flattened the inside and I wanna know how!

How about a picture?

sorry sdjohn, I don't know if when I return to the box where I did the work I will find the tool (I did it there because my angle grinder broken some days ago and I haven't bought a new one yet), maybe my brother will have already ended up in the garbage, because they are really 2 pieces of iron

btw I drew it quickly in cad, sorry if it's rough, just to give you an idea.
I was inspired by the manual sanders that pinch the sandpaper.
Imagine pinching the sandpaper between the 2 pieces of iron and screwing the 2 screws. I hope it could explain the "tool", as you can see nothing complicated

thank you! that makes sense. did you flatten your tool in some way before using it to make sure it was flat itself? i suppose you could make that, sand it on a pane of glass to get it flat, then wedge the sandpaper into it and use it to do the box....

yes exactly, as I wrote in the previous post (or at least I tried), I smoothed out on a pane of glass the lower part in contact with the sandpaper

That's really well done and so simple.

I was expecting you to say, "I took it to work and used the surface mill," or something. This is way better because we can all do it.

yeah, this is a smart simple solution. Well done sir

It worked well, but maybe there is something else strange in this engine, it is not air leak with the engine off 🤔

The pilot circuit and main circuit overlap at this throttle range.
Are you including cable slack at your marks?

What happens when you pull the choke with that main stack?

Jets sizes need to be checked, or at least compared to each other with a tapered needle.
The bigger sizes have the biggest deviation from stamped #'s
I'm not saying this is your issue, but it's another must.

Btw I'm sure you've seen this, but in case you haven't...
I learned more from the comments and replies than the video:

&t=20s

actually not, I have to check for cable slack, in case I will set again the scale here is really cold when I come back from work, so rides are really short, but will try as soon as possible I've already compared them, and bgm kit seems to be weel done, only I don't like the material on ACs, they flake off on the screwdriver cuts yes, sure, I know also personally those guys, they are really available to help people. Actually in this video I'm not agree with he said about pilot jet. Some time ago it got clogged on my previous carb and that's when I understood how wide the operating range was. If it hadn't been for the choke I would hardly have returned home...
I take a look on comments and replies but I can see only congrats and setup request posts. Maybe some had been deleted?

2 days ago I changed the gasket under the carb (for the first time) and now it seems to be richer and impossible to rev it up. Will keep you posted on which mj I will found to be acceptable.

Actually I didn't understand how to set mix screw correctly. I follow the guide but the more I screw the more it goes up and at a certain point (near to completely closed) engine tends to turn off. But it started to go out of run in a round way much earlier

in what engine do you use SI carb? he is saying that the pilot jet only works in idle and as soon as you touch the accelerator and vacuum is created to extract fuel from the maximum circuit, the minimum circuit stops working yes maybe I mistakenly never gave weight to the gasket under the carb
because thinking that there were perfectly flattened surfaces and its job was almost irrelevant Sorry, I am not able to well explain some concept. I'm trying to explain that at idle, when the mixer screw near to completely closed, the engine starts to run like when the fuel in the carb is about to end, like when you close the fuel tap for example and the speed increases. And when I close the screw completely, the engine turns off.
According to what the guide says, if I understood correctly, you have to leave the mixer screw in the point where the speed engine is higher, but in my case it would be too lean so have I to set screw following my feeling?

The mixer screw on the SI carb meters fuel flow into the idle jet, so airflow is fixed, the fuel amount changes the ratio. That's the opposite of most carbs, which meter air into the idle circuit, where fuel flow is fixed and the air volume is changed.

As such, you cut off off the fuel flow entirely when you turn the mixture screw all the way in.

I have three kitted bikes. Two BGM's and a VMC Stelvio.
One with a Cosa filter. One with no filter. One with Oopsclunkthud's bellmouth, 22mm Lemarxon sleeve and Polini airbox cover.
All with Polini box exhausts.

I've tried everything, jetting-wise.
It's funny if you think about it. None of these bikes were made for tuning, so recommendations for jetting are "try a T5 atomizer/AC combination, Rally slide, Cosa filter..." Funny.

Currently in the middle of a Malossi Sport project. I have in my notes not to go over a intake closing angle of 65 with the SI Thought he's referring to the end of the (much later) progression phase.
At WOT a lean pilot will not contribute to a seize condition.
But yeah, where are we in the throttle range most of the time on a kitted bike? Back it out a full turn from there and take it out. Set it for the most (smooth) power. It's difficult to tell if it's lean or rich without a hill, but half a turn in either direction will be better or worse.

yes correct, for carbs that have mixer screw between air filter and jet column, it would be like for the SI to have the mixer screw between jet and AC Oh so cool! 3 Vespas with 3 different inlet setups.. Which configurations do you have in your Vespas without filter and the one with Oopsclunkthud's bellmouth?
In my case it almost seems that in 1/4 throttle and high revs condition there is not enough vacuum created to extract enough fuel from the main nozzle.
Being a very common setup, either my engine has some other problem that is driving me crazy or people don't realize their engine run lean Maybe it's really better for blowback and for low rev torque. Which engine setup are you going to use? In my case, in highway with 1/4-1/2 throttle and high rev, exactly where I have the problem I will try to understand, but from tested i did on MJ and AC, mixer screw position was not necessary to be moved, only when I worked on pilot jet. Am I wrong?

'59 VNA on 8's
22mm sleeve no filter.
Twisty hill climber.

'78 & 79 P125's
One is my tourer with Oop's bellmouth and 22mm sleeve.
That combination is quite wild.
The other is my wife's (Stelvio) with a filter no sleeve.
All with Lemarxon atomizers and slides. I'm surprised few seem to be using them here. I don't think you can do any more than your 120/BE4 as far as getting the main jet stack to influence there. Are you still using the 4.0 slide?

It is a common setup!
Have you tried the pilot jet set?
I'd be surprised if that doesn't help your issue.

If not, and as you've solved your air leaks, "I'd" consider C'man's suggestion to add to squish. .9mm is very low with a 60mm crank with the MK2.
Static compression, .9 with a 57mm crank = 1.3 with a 60mm crank.
This would also explain your need for more-than-typical rich jetting and retarded ignition.
https://it.blog.scooter-center.com/malossi-210ccm-fur-vespa-px200-v2008-sport-mhr-erste-details-ii/

as far as I'm concerned, I contacted him some time ago for some details
but the seller has not been friendly and not very willing to explain his solutions.
btw, for testing I created a x234 starting from a be2, it's cold here and I didn't have a lot of chance to test it better, but with an AC160 it behaves strangely, I didn't understand the effect. Can you explain to me how it should behave? Yes, I am. Before fixing problem on carb box I tested also slides 5 and SIP 4.2, them make the afr richer at 1/4-1/2 throttle opening and low rpm, after 4500/5000 I think the air passes only from 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. I could try them now with carb box fixed or am I off track? pilot jet set arrived some days ago but I didn't have the chance to try it properly, I only put the ac160-68 but it was too rich at low rpm, probably a slide with a deeper cut-off would be needed maybe I didn't understand well, but 1.3mm on c60 setup is only to have same compression ratio the C57 has with 0.9mm because the cylinder head is common for C57 and C60, isn't it?
But I dug the dome to bring the compression ratio to 11:1 and reduce a little the squish band width.
anyway I will test it also because I want to follow your advice on cylinder timings

He is not friendly! Can you imagine how many ask him to explain things?
I've seen all of his Youtube videos 2-3 times. I wouldn't wish that on anyone.
They defy auto-translate.
As a baseline, the BE3 should work here.
It's super rare to see a BE4 other than in this group. The slide cutaway's influence is throttle position, not rpm.
You can simulate a flat slide by blocking the oval hole that feeds it at the top of the carb. If you only have the chance to do one at a time, try a 62/160 to see if that helps your issue.
As far as your concerns with a 160AC at the pilot..
The fuel size is important, but as the pilot jet is an emulsifier, the equation is also important (see pic). Wow.

I often struggle when the video is in English for idioms and technical terms, you can imagine in German… anyway I watched them a few times both with subtitles translated into Italian and English (the translations are always more faithful) and I don't think some points were touched upon for that reason I had asked a very specific question, not to explain everything to me and I didn't come across as someone who doesn't like studying, it would have been quicker to answer me or tell me that the topic had been covered in the videos and maybe I would have watched them again. He wasn't friendly with me but maybe I made a mistake in the way I asked the question or it was simply just a difficult day, it can happen to anyone, even if you're a salesman 🍻 Before to buy SIP 4.2 slide (flattened, without not cutoff on the bottom) I blocked the oval hole and the result was the same as the 4.2 slide, very rich at low rpm and middle throttle opening and behavior identical to slide 4 at high engine speed. So I mount slide 4 again because 4.2 enriched when, for my engine, it was not necessary
I still have to test it after the fix of the carb box, I hope something will change Thank you so much, I will try to put into practice 🙏
From the behavior I can see on my engine the pic is not respected, but probably my engine has some other problem..