Modern Vespa

Hi there!
I'm really don't wanted to start this thread as I thought that I can figure out all by myself.

But I can't.
I hope someone can help me with right jetting.

Prehistory:
P150X not matching ports with DR 177 and Malossi cylinder head.
Rotary intake
SI 24/24 E drilled 2.5mm: AC 160 - BE3 -125 MJ and 55/160 idle.
Original air filter with drilled holes above jets
Mazzucchelli racing crankshaft 57mm stroke
22/68 primary
SIP Road 2 exhaust
SIP Touren flywheel 1.6 KG
SIP fast flow fuel tap.

I ride on that setup near 7000 miles short in town and really long hard runs on the mountain roads. Everything was fine, plug colour is right, I can easily hold 55-57 MPH for a really long time and temperature holds on 275-285º F.

Then I change exhaust for Polini Box and like it more than old despite I lost 2-3 miles of max speed. Still runs perfect without any other changes.

And then I put new SIP T5 air filter and Polini carb case cover. Run for a long stretch and I see that the temperature is growing faster and already at 50 MPH it easily reach 300ºF and continues grow up. Obviously jetting is too lean.

Then I change idle jet for 50/140 and main jet for 128. But it seems that it not helps really.
So its time to play with air corrector and mixer tube?
I don't understand anything at all, please help me understand. Maybe there is some links where I can read about SI carb settings? TIA.









Last edited by roland87 on Tue, 11 Apr 2023 10:31:59 +0000; edited 2 times

I keep saying how good this filter and carb top are!

The Air Corrector is the air jet this will determine how much air can enter the emulsion tube. Popular trend is run this at 120 which is the least amount of air.

The atomizer is going to tune the low and mid range power. Popular trend is run this as rich as possible. I'm running the leanest so find which runs the best. I like factory smooth.

Tried my friend's all original PX125 and really like how smoot is it run. With Polini exhaust, Polini carb case cover and T5 air filter my P become much smoother than it was before.

Start with a 120AC this will richen things up. I tried a 110AC but went back to the 120.

You can try a larger mixer and see how that does. It's going to be some trial and error to find the best recipe. Think the higher temps could indicate better air flow with new filter. How does it feel?

I really like how scoot runs after all changes. Much more smoother and and more responsive to the throttle. Polini exhaust is also quieter than Road 2. Less vibrations and gets to 60 mph quicker.

AC120/BE4 and work from there. Usually about 115
It will be quicker once jetted better. With the polini exhaust it would pull a 23/68.

Thanks a lot for advice, Jack!
Already ordered AC120, 140 and BE4. Now need to order some main jets as the smallest I have is only 118.

Is it a real 60mph though? I had the polini on my DR177 and it was so disappointing top end. The road 2.0 will pee all over it top end and easily get to 110KHM indicated on speedo, , which in reality is about 64mph GPS. The polini could barely reach indicated 100 kmh, often it would hover about 95kmh and thats a big drop. I tried so hard to like the polini, i mean its great for local riding, two up, yes its quieter, but had to go back to the road 2.0, tried polini twice using all sorts of different tweaks but i could get no more blood out of that stone so road 2.0 back on.

Yes Ferris, I think its real 60 MPH. I measured lot of times with my smartphone app and with GPS speedo. I also have sip speedo so I adjusted it for have same results as on my phone app.
And yes - with Road 2 top speed was near 105-108 KMH but I very rarely ride with that speed as there is a lot vibrations and it seems that engine soon blow down.
With Polini top speed is 102 KMH and never more. But I really likes how this pipe works and power delivers.

Comparing your spec. with mine:

You
P150X not matching ports with DR 177 and Malossi cylinder head.
Rotary intake
SI 24/24 E drilled 2.5mm: AC 160 - BE3 -125 MJ and 55/160 idle.
Original air filter with drilled holes above jets
Mazzucchelli racing crankshaft 57mm stroke
22/68 primary
SIP Road 2 exhaust
SIP Touren flywheel 1.6 KG
SIP fast flow fuel tap


Me
PX150 with ports enlarged, matched DR 177, cylinder raised 1.0mm
VMC Super G cylinder head.
Rotary intake (inlet enlarged)
SI 24/24 E drilled 2.5mm: AC 120 - BE4 -115 MJ and 52/140 idle.
Venturi (OopsClunkThud/Shapeways) and stock autolube box top
Jasil racing crankshaft 57mm stroke
23/68 primary
BGM BigBox Touring exhaust
Stock flywheel 2.2 KG
BGM fast flow fuel tap

Very similar setups, although I have done some porting/enlarging/matching and raised the cylinder for better port timings. For a DR177, it has really good power and ~62 mph/100 kmh top speed. It is very solid and reliable.

I agree with others that AC120 and BE4 is the way to go, especially with a venturi, or in your case a T5 filter and increased air box volume. Also, if you have the power, the 23T clutch is a good move to get the best top speed.

The DR is a very vibratey noisy kit. When mine first went on I seriously thought there was something wrong with it. Have you noticed on start up how rattly they sound, then when it heats up it calms down considerably. I was getting some vibration with my setup and also with the polini box. Since rethinking all of the jetting with some advice and me experimenting , the vibration is a lot less and 60mph gps with the road 2.0 is so much better. I upped main jet from 122 to 124, changed the air filter to have smaller drill holes above main and pilot; this made driving so much better so my vibration must be due to being a tad too lean. Just found it hard going from road 2 to polinibox, i so wanted to like the polini but the lack of top end frustration for dual carriageway overtakes was annoying.

Thanks for the tip Swa. I tried 23T clutch before I put on Malossi head and T5 filter with Polini carb cover. It was good on highways but terrible in town use, esp. when changing 3rd to 4th gear. Terrible lack of power on 4th or need rev really high on 3rd.

I'm really thinking to put short 4th gear when I need next time to open cases.
But I also have old 6 springs clutch with 23T cog. So when I will end sort the carb settings I try put again 23T. If it will be ok then I will be order 23T for my Cosa clutch. Yes I noticed it and was very confused when start engine at first time. But now already done more than 12000 km on this engine with no mercy to it on long highway trips or on mountain roads and it still feels ok. So I think its really good reliable kit.

Definitely reliable , It's my daily work horse . Not that exciting but a good performance boost over standard 125/150.

I'm not adding much for what have been said, but, why did you felt the need to fit the SIP T5 air filter and the bigger carb case from Polini? It seems it was riding fine with the Polini box only loosing those 2-3 miles of top speed ... which is what I would expect changing the SR2 to the Polini box.

SIP tested (YT video) a bunch of box exhausts on dyno and the Polini delivered more power on low/mid revs and less in high revs than the SR2, hence the lost on top speed.

The price on the T5 filter and carb cover was so good that I could not refuse. Also mesh on my original air filter is torn in few places and I already thought about buying new filter.

So as my order with AC and mixer tube is still on the way I decide to try bit richer idle jet.
Swapped today 50/140 for 52/140. Tomorrow will see how it goes.

Yes, like I said, IF you have the power

I do not know about the older P150X gearbox, but my late PX150 has the same gearbox as a PX200, but with 68T primary. Therefore, I have a 35T 4th gear and a BIG gap from 3rd. Mine is ok with the 23T clutch, but I did consider a 36T clutch gear like the PX125.

The only what I remember for sure when I opened cases is that my gearbox have 68T cush drive cog and 35T 4th gear sprocket.
And this is not EFL gearbox with old type of cruciform.
And my P is VLX1T 337318 and motor is VLX1M 339705 so it 1981.
It also was with points 12V Ducati ignition.

But now I confused what exactly I gearbox I have according to this https://drive.google.com/file/d/1riP6fNWz424xY6KW31QrH-w2uwnwAwA_/view?usp=sharing

Thanks for input mate.

Today I received pair of AC(120 & 140) and mixer tube BE4.

Now it's noticeably colder. In the morning temperature is 8ºC(46ºF).
And now on my way to work engine temperature is less and seems not so scary as when there was more warm weather.

Nevertheless I changed the main jet stack to:
AC 120
Mix BE4
Main Jet 118
Also changed idle jet back to 50/140(2.8) as with 52/140(2.69) spark plug looks too black.

I made small test run and was impressed and confused how scoot is accelerating now. Really much better than with old jets.

On next three photos is spark plug colour(as camera distorts in reality colour is more dark) with:
Polini Box exhaust
Polini carb cover
SIP T5 air filter
AC 160 mix BE3 mj 128 ij 52/140
There was near 12ºC(53ºF)

And for comparison on last two photos is spark plug colour with old set up:
SIP Road 2 exhaust
Original low carb cover
Original 20/20 drilled air filter
AC 160 mix BE3 mj 125 ij 55/160
There was near +25ºC(77ºF)


AC 160 mix BE3 mj 128 ij 52/140

AC 160 mix BE3 mj 128 ij 52/140

AC 160 mix BE3 mj 128 ij 52/140



AC 160 mix BE3 mj 125 ij 55/160

No photos with 120ac?

No photos yet. Just installed it yesterday evening. And this morning make near 40km on my way to work.
Scoot runs great.
But temperature is still too high as for me. I hold 85 km/h for maybe 5-6 km on highway and temp easily gets to 150ºC(302ºF) outboard temperature is just 10ºC.

Now thinking about what jet I need change to richer - idle or main?

Ride a bit but not enough for sure with this jetting:

AC 120
Mix BE4
Main Jet 118
Idle Jet 50/140(2.8)

And noticed that temperature grows much faster when I on WOT than when I holds near 85 km/h it a little bit less than 1/2 open throttle.

I also decide to mark throttle grip and change MJ to 122. Hope tomorrow I can ride enough to understand more.

This jetting shit really makes me mad

With this setup:
AC 120
Mix BE4
Main Jet 122
Idle Jet 50/140(2.8)
Mix screw 2.5 out
It seems that engine temperature grows not so fast but also not so perfect when it was when outboard temperature was much warmer.
And I noticed that scoot jerks when throttle near 1/4. And this chaotic - sometimes all OK, sometimes it can jerks one or two times when throttle holds, sometimes when I open throttle from 1/4 it jerks once and then gains speed perfectly without any problems. It is LEAN or RICH idle jet?

When I ride with high RPM's and then pull clutch and close throttle engine back to idle very quick, maybe with one or two seconds. And the motor behaves like this with any jetting I have tried. AFAIK this is an indication that idle jet is not lean.

Today I changed idle jet to 52/140(2.69) and ride 120 km. It seems that jerks near 1/4 throttle became more pronounced and frequent.
So I need more leaner idle jet?
I drop in 55/160(2.9) and hope tomorrow weather is fine for testing.

And here is plug colour with
AC 120
Mix BE4
Main jet 122
Idle jet 52/140(2.69)
Mix screw 2.5 out


AC 120 BE4 mj 122 ij 52/140(2.69) mix 2.5 out

AC 120 BE4 mj 122 ij 52/140(2.69) mix 2.5 out

AC 120 BE4 mj 122 ij 52/140(2.69) mix 2.5 out

I think you are running too rich (AC too small) and maybe try the 1.5 turns idle screw. But then BE4 leans a bit at high rpm which may be not safe. Your 1st post setup is pretty standard for that engine and a SI24/24E… buy hey, I don't want to thrown more sand into a so beaten subject, knowing that every engine is unique and what works for me might not work for others.

My BGM177 is heavily ported in a 125 GTR crankcase (3 window), Sip Road 3.0, variable advance (8 deg) Electronic Ignition, SI24/24E (drilled), drilled filter, matched engine intake, extended intake crankshaft, etc. and I'm running 160/BE3/138 and 55/160 - works flawlessly at every rpm… so… ? You have to keep trying and surely will find the right jet settings …

Mixture screw?

Thanks for tips.
But if it too rich the temperature must not get so quick and so high?
I paid so much attention to jets that forgot I have AC 140 and BE3 mixer.

Making a lot of changes at once make it more difficult to distinguish what changed and what needs changing.

Might be a good idea to start with the 120AC. That is and might be a governor something that may not change and will be the one thing that determines everything else.

Plug your original jetting BE3-125/128 55/160 with the 120AC. Can you feel the change is it better worse? Then after you have a feel for how it was and how it is with the 120AC plug in the BE4 and see what it does good or worse. This way you know how each jet is affecting the result.

Keep notes so you have an idea on what is going on.

Brief thread hijack & preemptive apology: @roland what's that polini airbox lid like? Looks suspiciously identical to my pinasco one, which nonetheless requires a spacer beneath it to fit the T5 air filter. Is the polini one taller?

Also, does the back end of it ever scrape against the px's frame ever so slightly, like the pinasco lid does?

Thanks!

Got the same combo for my P. Haven't seen the Pinasco up close but they look the same, except the nice plug for the idle screw and the standoffs for the mounting screws (red circles). It definitely touches the filter (red arrows) but I'll reshape it with the heat gun. Without a spacer it won't touch the frame...

The Polini needs a DRT spacer too, according to SIP's description. I run my Pinasco one with a venturi, not a T5 filter. It's flimsy and ill fitting, and the idle screw is difficult to line up with the hole. I like the 'standoffs' on the Polini, as noted by SaFiS, as it's a pain to locate the screws on the Pinasco

I actually find the pinasco lid a far sight easier to line up the screws with, at least compared to the factory cover. Worth the 50 bucks right there.

Re. Shaping the airbox with heat -- didn't even think of that. Thanks for the tip! There are two spots where it kind of chafes against the PX frame - I'd expect a heat gun and the back end of a spoon might do the trick.

*End thread hijack*

Stick in an ac140, BE5, a 125/124 main and a 55/120 pilot 3 turns out rich. If you want to push 1 or 2 mph extra top end, drop the main to 122, but its right on the margin for slightly lean. Go try it, report back. Its ers on the side of caution for a richer setup so you wont blow anything up trying,. I have a dr177, drilled filter, fast flow tap, road 2.0, 24si, it runs perfect and its pretty quick for what it is, non ported bolt on. Genuine 64mph gps without any gimmicks or faffing about. Yes you got a different head, but this not going to yield anymore top end over standard IMO. Use a 7 rated heat plug for local thrash abouts and go to an 8 for long 50mile run outs. If its getting cooler where you are now, it is here in the UK, things will lean up a bit too with colder air so jetting above is a good setup for a DR, so if you do ok with the 122 MJ, up it to 124 to compensate for the colder weather change to come. Ive been faffing about with jetting with the DR for 2 years now, minor changes etc and what ive arrived at is perfect, finally.

JimVanMorrissey I never have Pinasco lid on my hands. But after SaFiS input about reshaping lid I think I need do the same. Now idle screw is not even not close to line up with hole in lid. Maybe reshaping helps here.

Great advices mates! Thanks hibbert, ferriswolf and SaFiS.
Seems that I need reshape lid too.
Next.
I have no BE5 at the moment, but I already ordered it.
Now I ride few days with:
AC 120
BE4
MJ 122
IJ 55/160
Mix 2.5 out

It seems not bad and temperature not so crazy as before but it also seems too rich. And sometimes it have some jerking near 1/4 throttle.
I want ride few days more and check plug color. Yes I know this way is not right as plug chop but always works for me for previous 12 000 km.
Also outboard temperature now between +8 and +16ºC so obviously it affects on engine temperature.

Next step I thinking to try AC 120 or 140 with BE3 and 125 or 128 main jet and 55/160 idle. And then work from there.

You got the furthest rich AC (120) and the furthest rich mixer (BE4), why not pop the AC to 140 first then give that a whirl with what you have got, i think you will notice improvement in running. Ive run my DR with a BE4 ac140 122main but it was way too rich as I couldnt pull past 58mph WOT GPS. So dropped leaner to BE5 but upped main to 125 now get to 62mph, if drop main to 122 can reach 64mph but its heading lean. I also richened the pilot slightly. It has a very slight gurgle on tiny throttle, a pop pop, but small compromise for good performance and safe driving. I dont have a CHT but done plug chops across all throttle conditions and a nice chocolate brown which is how ive always gauged scooter carb fuel mix.

Can I suggest shelving it all and going back to Prehistory for the season?
Seemed like a great setup!

The filter doesn't have to be in perfect condition to work. Blast it with carb/brake cleaner and ride out the season. Bellows to frame is already a huge filter.

You're juggling too many chainsaws this late in the season, IMO.

Ray8 you absolutely right. But it is boring to do nothing. I like to spend time with my Vespas And I also want to learn more about SI carb settings, not only how to change main jet.

Checked plug today. It is after 150-170 km with:
AC 120
BE4
MJ 122
IJ 55/160
Mix 2.5 out
Obviously too rich.

Keep generally the same but change to BE3. Adjust the main jet down starting at about 128 to confirm WOT is still rich.

It's a nice feeling when the SI carb is as smooth as factory stock but a lot faster. Saves loads on fuel too.

So I stay with AC120?

Yes, AC120. Once the main jet is set correctly at WOT, the size will determine the next steps.

@roland87 -- I'd followed Jack221's advice there on jetting and am very pleased with the results. This factory-like smoothness is immensely satisfying. Keep going!

(I'm on a 120/BE5 stack on an SI24, except with a Malossi 221 setup, and landed at a 128 main jet.)