Happy with Polini Venturi for 20/20
Post Reply    Forum -> Not-So-Modern
Author Message
Member
VLB1T
Joined: 12 Mar 2010
Posts: 20
Location: SF Bay Area
Fri Jan 11, 2019 1:51 pm quote
So, I've fallen down the rabbit hole called "buy things for Vespa so it goes faster!" I love it, but it's expensive.

This lead me to buy the Polini Venturi for my 20/20 SI carb.

I have the SIP fast fuel tap, Pinasco 2-port 177, and SIP Road 2.0

I have to say, I'm very pleased with the result. The kit came with a 115 main jet, which worked great.

I also got the SIP kit of performance jets (up to 128). They all seemed to work - even the 128.

There was maybe a slight hesitation in revs from idle to WOT with the 128. I eventually settled for the 122.

I've only just installed it. I'll have to check my plug in the coming weeks of riding.

Have any of you tried this? What main jet worked the best?
Ossessionato
2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
Joined: 26 May 2013
Posts: 3735
Location: Millbin, Ostrayleea, mate
Sat Jan 12, 2019 8:31 pm quote
Screwed?
Take care to secure (thread tape or loctite) the screw that holds it down... I've heard a few times that they fell out & went down the hole into motor, which is a bad thing
Ossessionato
1976 Super (x 2), 1974 Primavera (x 2), 2006 Fly 150
Joined: 26 Sep 2013
Posts: 4521
Location: So Cal
Sun Jan 13, 2019 8:45 am quote
122 sounds about right. With those venturi’s I think a good rule of thumb is at least 10 sizes bigger on the main. Watch the plug and the temps. I used a 122 main (up from 112) with oopsclunkthud’s bellmouth/venturi (similar concept to the Polini) on my 177 with a 20/20 carb. Ran fine.
Member
GT 125 (03), PX 166 (99)
Joined: 19 Nov 2017
Posts: 22
Location: Nr Exeter Devon UK
Mon Jan 14, 2019 12:55 am quote
Best to go massive and work down,. not the other way round,.
pek
Enthusiast
PX125E
Joined: 06 Oct 2018
Posts: 65
Location: Gravesend, Kent, UK
Fri Jan 18, 2019 5:41 am quote
Air filter
Hello.
Are you using the foam air filter and have the side panels/Cowls on?
I have a Venturi kit which came free in a box of bits when I bought the scooter and have concernes the air would be much hotter and affect the carburation.
I expect you Guys in the USA would know best given the weather difference.
Member
P200e, ss90
Joined: 05 Feb 2018
Posts: 36
Location: NZ
Fri Jan 18, 2019 12:21 pm quote
Re: Screwed?
SubEtherBASS wrote:
Take care to secure (thread tape or loctite) the screw that holds it down... I've heard a few times that they fell out & went down the hole into motor, which is a bad thing
Just a second on this from Seb. Had something similar on my smallfame carb for airflow. Took it for a blast down the motorway. Got to 100kph on the phone whick i was pretty stoked with. At the offramp it continued reving like a beast. Thought airleak, but when i checked, a fixing screw had vibrated loose and sucked into the carb, jamming the throttle slide. So lucky it went longways. God knows what would’ve happened if it reached the crank! I lock that stuff in now.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 111
Location: Cornwall UK
Fri Jan 18, 2019 1:11 pm quote
Threadlocking the bolt is a must-do, but it's a drag if you're fiddling with the jets, so I Dremelled a cut-out allow access to them without removing the vortex:

Vortex Cut Out.jpg

Member
GT 125 (03), PX 166 (99)
Joined: 19 Nov 2017
Posts: 22
Location: Nr Exeter Devon UK
Sat Jan 19, 2019 2:19 am quote
I also done the same mod as sime66 (thanks for the tip),..
Very good idea,... as a lot of tweaking needed !!!!
pek
Enthusiast
PX210 Polini
Joined: 07 Jun 2018
Posts: 54
Location: Yorkshire
Sat Jan 19, 2019 3:01 am quote
Do MPGs take a big hit with the Venturi fitted.
Ossessionato
1976 Super (x 2), 1974 Primavera (x 2), 2006 Fly 150
Joined: 26 Sep 2013
Posts: 4521
Location: So Cal
Sat Jan 19, 2019 5:06 am quote
Yes
Member
GT 125 (03), PX 166 (99)
Joined: 19 Nov 2017
Posts: 22
Location: Nr Exeter Devon UK
Sat Jan 19, 2019 5:16 am quote
Not sure if BIG jump ,but i,m getting around nine miles per litre ,(cant remember before),
Running venturi (with ram air filter), malossi 166, 24/24, pm pipe,...
pek
Member
VLB1T
Joined: 12 Mar 2010
Posts: 20
Location: SF Bay Area
Mon Jan 21, 2019 12:33 pm quote
Re: Air filter
worrywort wrote:
Hello.
Are you using the foam air filter and have the side panels/Cowls on?
I have a Venturi kit which came free in a box of bits when I bought the scooter and have concernes the air would be much hotter and affect the carburation.
I expect you Guys in the USA would know best given the weather difference.
Hi, Worrywort!

Yes, I'm using the foam air filter and the cowls are on. As for the hotter air affecting the carburation, I can't really say yet. It's too soon. Compare the weather online between your address and San Mateo, CA, USA. I can't imagine it's so different as to make a difference. Maybe a little bit drier here?

I would recommend you dial-in your bike without the venturi. When you add it, you will probably be able to better appreciate the difference!

My kit was sold with a 115 main jet. More experienced people than I recommend going big first, and testing ever-smaller main jets till you get something that works.

Good luck!
Hooked
PX 150
Joined: 15 Sep 2006
Posts: 460
Location: Gold Coast, Australia
Mon Jan 21, 2019 2:36 pm quote
It hasnt been mentioned here but in other topics the venturi needs a higher volume airbox lid to be effective.
The standard lid sits to low above the venturi and negates any advantage of using it in the first place, creates a choke type effect.
If indeed you do notice a power increase. It indicates that your previous jetting was somewhat lean and youve corrected it to some degree.
Also pulling the choke on would have a similar effect.
Member
GT 125 (03), PX 166 (99)
Joined: 19 Nov 2017
Posts: 22
Location: Nr Exeter Devon UK
Tue Jan 22, 2019 6:06 am quote
Correct Jimscoot,.. when also using bigger pinasco box - even more sexy !!!
But a little expensive.
Pek
Ossessionato
05 Stella, '62 VBB, 76 Sprint V, 63 GL
Joined: 16 Jun 2011
Posts: 2008
Location: Chicago. Well, Evanston, but that's almost Chicago
Tue Jan 22, 2019 6:30 am quote
Can also pick up an airbox spacer.

I think that SaFis and/or V oodoo have 3D Printed them, too. Maybe they have a STL file or thingiverse link they can share.

Unrelated, when I did my cursory thingiverse search, I found this, which could be an interesting project...Gasket Tracers for making your own gaskets. Not for Vintage in this instance, but a cool idea for high-use gaskets, e.g. carb base. Just need to draw them up.
Veni, Vidi, Posti
a herd of easy shifty rats
Joined: 22 Nov 2010
Posts: 6733
Location: seattle/athens
Wed Jan 23, 2019 10:30 pm quote
Airbox riser
I made one of these from the Thingaverse file. After tweaking the scale factor I got it to fit the airbox cover perfectly - just something I wanted to try, next time I get a parts order together I'll include a fatty T5 air filter for a .02 HP gain!

Here's the link https://www.thingiverse.com/thing:1054950

Quick action throttle pulley or smallframe door bushings or ... ? There's a lot there & all free - here's something else I'll be trying:

Electrical_Connector_preview_featured.jpg

Member
VLB1T
Joined: 12 Mar 2010
Posts: 20
Location: SF Bay Area
Mon Feb 04, 2019 10:47 pm quote
I thought I was done. I was so wrong!
jimscoot wrote:
It hasnt been mentioned here but in other topics the venturi needs a higher volume airbox lid to be effective.
The standard lid sits to low above the venturi and negates any advantage of using it in the first place, creates a choke type effect.
If indeed you do notice a power increase. It indicates that your previous jetting was somewhat lean and youve corrected it to some degree.
Also pulling the choke on would have a similar effect.
As Jimscoot noted, the airbox sits where it does, and this is probably just too low to really get the benefit of the venturi.

So today I drove it a bit with the carb lid off.

Oh my God! The front wheel leaves the ground!

Time for more tuning, my friends. Larger airbox lid, larger gasket (should increase space by about 40%). I'm also picking up a BE2 mixer tube and more main jets.

Go big or go home!

Further updates coming. If I can't control myself, this will escalate into a better clutch, or up-gearing - that wouldn't be the worst thing, now would it?

Thanks, everyone, for the advice!
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1130
Location: London UK
Tue Feb 05, 2019 12:42 am quote
Don't get me wrong, I'm all for enthusiasm, however, when performance is increased by removing the box lid (or stock filter on stock engine) it just means the jetting is too rich (usually the pilot jet).

I would suggest getting the larger box gasket. And for comparison, I have a standard EFL carb box on my Tourer, with a SI26/26E and Pinasco VRX Vortex and still makes 20bhp.

btw, A BE2 atomiser has no place on a kitted engine.
Ossessionato
1976 Super (x 2), 1974 Primavera (x 2), 2006 Fly 150
Joined: 26 Sep 2013
Posts: 4521
Location: So Cal
Tue Feb 05, 2019 5:06 pm quote
Jack221 wrote:
btw, A BE2 atomiser has no place on a kitted engine.
Why so? I use a BE2 in one of my kitted Supers, and it’s been a strong & solid runner for 5000+ miles now.
Rallies Europe 2016   Vespa Wasp Pin Badges   Yelcome Leather Top Cases and Roll Bags for Piaggio Vespa PX LX LXV GTS GTV
Post Reply    Forum -> Not-So-Modern
[ Time: 0.3300s ][ Queries: 26 (0.0473s) ][ Debug on ]