Help for choosing a gear ratio and a carburetor...
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P125X
Joined: 15 Sep 2020
Posts: 3
Location: Portugal
Tue Sep 15, 2020 1:37 pm quote
Hi. I've been looking for another post on this, but didn't find it, so I'm writing my first post on this forum to ask for help...

I've wrecked the rotary valve on my P125X and I'm converting it to reed valve. I have a reed block from DRT that was bought for a Rally 200 but never installed that I'm going to use on this motor. Its a flat reed block, with 3 Polini petals. I'll need to work the crankcase a bit, but I think it will fit. I think I'll fit also a new crankshaft, probably a SIP bell-shaped one. I also want to change the gear ratio, to a longer one. I have a stock clutch, with 22 teeth, for a 67 teeth primary gear. I already have a DR 177 installed and a custom exhaust, something like as improved SIP Road 2.0

So, the help I need is especially for the choosing of the carburetor and jetting, and for the clutch and/or primary gear:

1. I'm leaning towards a Mikuni TMX 27 or 30 Flatslider, but I'm not sure if it's not too much, or if i need to change the jets it comes with

2. I think the stock clutch is too weak and i need a new one. I believe a Piaggio Cosa 2 standard is a good choice, but i also need to change the clutch cover and the primary drive, right?

I want this ride to be a everyday ride, it's not meant to be a racing Vespa, but I want to have some power if I need it, and, if possible, I don't want to wreck my bank account...

Thanks in advance for your opinions!
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2443
Location: London UK
Tue Sep 15, 2020 9:22 pm quote
1. Dellorto PHBH 30 is the best choice if you know little about jetting.
2. Cosa 2 banded clutch with Sip CR80 plates
3. 22/67 gearing is plenty high enough
4. If buying a bell crank get a 60mm
Lurker
P125X
Joined: 15 Sep 2020
Posts: 3
Location: Portugal
Thu Sep 17, 2020 12:09 am quote
Jack221 wrote:
1. Dellorto PHBH 30 is the best choice if you know little about jetting.
2. Cosa 2 banded clutch with Sip CR80 plates
3. 22/67 gearing is plenty high enough
4. If buying a bell crank get a 60mm
Thanks!

Dellorto PHBH 30 was my first choice, but the Mikuni seemed better, and I didn't have the ideia that it would be much different to set up... But, yes, my knowledge about jetting is scarse... Maybe I'll save some money and buy the Dellorto.

I assume my stock crankcshaft has a stroke length of 57mm. As I look further, I understand that either 57, 60 or 62mm fit on my Vespa. But I'm not that confident: there is a 5mm difference from 57 to 62mm. If I change the stroke length is there any other adjustment I need to make, or these 5mm are still in the tolerance range? And, as keep asking things: would you choose a bell shaped or a full circle crankshaft? The more I look, the less certain I get, lol...
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2443
Location: London UK
Thu Sep 17, 2020 5:31 am quote
Muito bem. For your DR kit a 60mm crank works. Needs no modification. Only need fit a 1.5mm base packer plus the gasket. This will run stronger than the 57mm. Bell crank is more suited to general use and full circle for more always wide open or race use. This is not a hard rule but depends on port timing. Bell crank for your needs and your DR.

PHBH is all you need and set up can be quick but you will need to learn a little for it to run really well.
Ossessionato
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 2853
Location: Nashville
Thu Sep 17, 2020 7:11 am quote
Yes, there are other changes you'll need to make with the 60mm crank.

You're about to descend into the never-ending labyrinth of Tuning
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7954
Location: Victoria, Australia
Fri Sep 18, 2020 12:54 am quote
A mate bought a TMX30, and found there were very few options available re needles, jets and slides. Plenty for the 35's and 38's but not the smaller ones apparently.
Lurker
P125X
Joined: 15 Sep 2020
Posts: 3
Location: Portugal
Tue Sep 22, 2020 2:37 pm quote
Ok, so I've decided and already ordered everything I need...
For the carburetor, I've opted by the Dell'Orto PHBH 30. The crankshaft is the
Flowed Crankshaft SERIE PRO by Worb5 (SIP). The clutch is the BGM Pro Superstrong CNC, with 23 teeth. I chose the 23 teeth because I already felt that I needed another gear with the setup I had.

Now I wait for everything to arrive, and use the time to dremel out some aluminum from the crankcase!
Hooked
vespa 125 vnb1t
Joined: 13 Jul 2011
Posts: 367
Location: antibes , france
Fri Sep 25, 2020 10:35 am quote
scooter factory phbh carbs
this may be helpful to some folks
Scooting the Ozarks is a scooter rally held in Eureka Springs, Arkansas offering riders scenic twisty rides, poker run, and more.   Vespa Wasp Pin Badges   AF1 Racing Vespa Austin
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