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Vespa P125X
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P125x
SIP road 2.0
24.24

After giving up with my DR 177, have recently fitted a VMC Super G 177. What jet stack/ carb combination have people settled on? Same as DR or different?
@ray8 avatar
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Molto Verboso
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Molto Verboso
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craigyc wrote:
P125x
SIP road 2.0
24.24

After giving up with my DR 177, have recently fitted a VMC Super G 177. What jet stack/ carb combination have people settled on? Same as DR or different?
VMC Stelvio (alloy cylinder vs your Super G):
140ac with a drilled/Cosa filter. Rode similar with a 160ac and original filter.
BE3
128mj city. 130 touring.
55/160 pilot jet.

All modified bikes are different, as well as your weight, gearing, climate, etc...

This "should" sort you out. At the least, you'll have a jet set from the same manufacturer, and not chase your tail as much as otherwise:
https://www.scooter-center.com/en/carburettor-tuning-kit-nozzle-set-bgm-pro-for-vespa-px125/150-with-bgm-pro-177-cylinder-kit-main-jet-set-secondary-jet-mixing-tube-air-correction-jet-bgm1770nej
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Style Maven
'74 50s x3 '87 PK125XL '92 PK50XLS Plurimatic - & - '58 AllState '68 Sprint '66(?) Super125 and '72 DanMotor Super150
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Thanks for that ^^^, some good info here. Seems like a good set to have for most any similar kit. And what do we think of this logical comment?
Quote:
AIR FILTER
The engine's jetting requirements are heavily dependent on the air filter used. The stock air filter doesn't look like much of a performer, but it is not a throttle. So there is no need to replace it with a funnel, venturi or even omit it altogether. The SI carb is very sensitive to changes in/on the air filter, so it should be kept and not modified for a good basic setup. The bottom of the air filter has a heart shaped cutout. This sits over the jets of the carburetor when installed. It is often recommended that this be drilled out or even removed altogether. This has a great influence on the mixture formation and can quickly lead to a dangerous lean. Changes should not be made in this area at the beginning.

Note: There are series air filters which already have two holes (Ø6+Ø8mm) ex works. These filters originate from the Vespa Cosa models, which have a second air filter and therefore completely different requirements for the mixture formation. Replace this filter if possible with the closed type of the PX models.
I know that serious Cosa ppl usually say that to run properly don't mess w/ the carb, weird Cosa air bellows or the filter plumbing to the second big filter under the seat.
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Thanks for this. I will have a look through the info.
i should note a couple of things. The air filter is a px200 with pre drilled holes. And today when I went for toodle it was 40 deg C (Dubai). The CTG quickly got up to 350 deg f with quarter throttle and doing 60-70k. This was a lot quicker temp rise and at lower speed than the DR. I would lean off the throttle a little and the temp would come down. The high temp at low speed makes it dangerous to ride here in Dubai. How do I reduce the temp for 1/4 to 1/2 throttle. Still running in also.
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2007 Stella 225
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UTC quote
craigyc wrote:
Thanks for this. I will have a look through the info.
i should note a couple of things. The air filter is a px200 with pre drilled holes. And today when I went for toodle it was 40 deg C (Dubai). The CTG quickly got up to 350 deg f with quarter throttle and doing 60-70k. This was a lot quicker temp rise and at lower speed than the DR. I would lean off the throttle a little and the temp would come down. The high temp at low speed makes it dangerous to ride here in Dubai. How do I reduce the temp for 1/4 to 1/2 throttle. Still running in also.
This may help,

Guide: SI Jetting Chart + How to Tune an SI Carb
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Hooked
px 125 disc
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My super g with a polini box and a drilled filter is running well on ac160 be3 mj128 and a 55/160 idle. Remember all bikes are different but it will give you a ball park of what you are aiming at. Remember the mantra jet rich and work your way down. I started with a 135 main.
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Molto Verboso
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My is
AC 120
BE 3
125
55/100
Mix 2.5 out

Polini Box, ports not matched, original drilled air filter and drilled SI 24/24

Maybe this thread give some help.
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Vespa P125X
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Thanks for all the direction. Just been out for a 100km run. It's 35deg c.

From the guys who gave me their stack numbers I have put in:
AC 160
BE3
MJ 128
55-160

For context:
P125x
Unported
Px 200 filter with holes
24.24 carb
SIP Road 2.0
Temp 35 deg c

Still running in so only between 1/4 and 1/2 throttle

Starts first kick (new one on me)
1st, a little spluttery but not 2 bad through to half throttle. Could be smoother.
2nd fine
3rd fine, occasional quick stumble. Kept slowly accelerating when throttle kept between 1/4 and 1/2.
4th, fine. Kept slowly accelerating when kept at between 1/4 and 1/2 throttle comfortably upto just over 80km/hr

However, still getting hot. Not as bad as last week. But in long runs had to keep at 60-65ish to keep at 330deg f.

I will follow the guidance on finding optimal jets etc once I have run in and can take to WOT. But anything anyone can point wrt the temperature?
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Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
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Jet Eye Master
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330F is not a little bit hot for crusing round on half throttle. The AC160 is way too lean, especially with a drilled filter. AC120 will run much cooler. More power at high rpm too. Will likely need a bigger pilot jet before it's finished.
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UTC quote
craigyc wrote:
Thanks for all the direction. Just been out for a 100km run. It's 35deg c.

From the guys who gave me their stack numbers I have put in:
AC 160
BE3
MJ 128
55-160

For context:
P125x
Unported
Px 200 filter with holes
24.24 carb
SIP Road 2.0
Temp 35 deg c

Still running in so only between 1/4 and 1/2 throttle

Starts first kick (new one on me)
1st, a little spluttery but not 2 bad through to half throttle. Could be smoother.
2nd fine
3rd fine, occasional quick stumble. Kept slowly accelerating when throttle kept between 1/4 and 1/2.
4th, fine. Kept slowly accelerating when kept at between 1/4 and 1/2 throttle comfortably upto just over 80km/hr

However, still getting hot. Not as bad as last week. But in long runs had to keep at 60-65ish to keep at 330deg f.

I will follow the guidance on finding optimal jets etc once I have run in and can take to WOT. But anything anyone can point wrt the temperature?
With a drilled filter you're effectively increasing the ac's size.
160 no holes, 140 drilled/Cosa filter, 120 no filter worked similarly here, and safe.
You're close to a 185 ac/stock filter with that 160.

The ac both leans/richens and determines when the main circuit initiates.
Smaller = earlier.
A 120/Cosa filter initiated the circuit too early at this level of tune.
I couldn't get it to work as both a city traffic rider and cruiser.

The slide cutout is most in play at mid throttle. You can test its leaning/delaying influence from around 1/4 to 3/4 throttle by taping over the oval hole at the top of the carb that feeds it.

Go baby steps! One change at a time or you'll go nuts.
First step 140 ac, or filter without holes.

Adjust the mixture screw on the road. From a rolling stop in second it should pull smoothly up to 1/4 throttle (where that circuit is dominant). This can be anywhere from 1.5 to 4.5 turns out.

Btw I'm assuming you have enough fuel flow and no air leak(s).
Fast flow tap. Channel from the bowl to the mj drilled to min 2mm.
8mm (5/16") x 24" fuel hose. Hopefully a carb reworked in Europe vs a Spaco out of the box.
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Hi Ray and Jack,

Thanks for this.

I have a 140AC so can try that, i will buy a 120AC also, but dont have an undrilled filter (would you recommend to replace?).

I have read about the drilling of the float bowl but dont undersatnd why. Any threads here for my understanding?

I have a fast flow tap, new ish fuel hose and the Dellorto 24.24 is also new ish.

Jack, you mention larger pilot jet, what should I get my hands on?
@roland87 avatar
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Molto Verboso
'13 LML Star 200, '81 50 Special, '81 P 150 X, '87 PK 50 Nuova, '84 PK 50 S
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Molto Verboso
@roland87 avatar
'13 LML Star 200, '81 50 Special, '81 P 150 X, '87 PK 50 Nuova, '84 PK 50 S
Joined: UTC
Posts: 1139
Location: Ukraine. Kyiv.
UTC quote
UTC

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
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Location: London UK
 
Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
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Location: London UK
UTC quote
craigyc wrote:
Hi Ray and Jack,

Thanks for this.

I have a 140AC so can try that, i will buy a 120AC also, but dont have an undrilled filter (would you recommend to replace?).

I have read about the drilling of the float bowl but dont undersatnd why. Any threads here for my understanding?

I have a fast flow tap, new ish fuel hose and the Dellorto 24.24 is also new ish.

Jack, you mention larger pilot jet, what should I get my hands on?
Undrilled filter is ok. Start with the AC140 you have. Reduce the Main jet size from splutter, until WOT feels heavy, then reduce one more size until it feels good and revs freely. Once you have this jet size, the rest can be determined. Only worry about WOT for now, all the other coughing and spluttering is easier to fix when WOT is done.

The pilot jet needs to be much bigger than stock. Typically on a bolt on kit a 50/100 will adjust in close enough. If you have a BGM set of the 58/160 to 68/160 sizes these can be enough to work.
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