Are dual carb Vespas REAL?

Jason ( ͡° ͜ʖ ͡°) /

Ok, I have spent the past day reading every thread on MA that mentions dual carb Vespas in their entirety, and resisting the urge to resurrect 10 year old threads. There are quite a few. But so far, every thread has just been discussion and no evidence of any action. Lots of people wanting to do it and then nothing. Who knows, maybe I will end up the same. But, the pinasco case halves have become so cheap on treats I decided to pick one up and try this, and I'll either drill a hole in a stock crank or Benji is trying to source the mazzy special crank with the web and hole.

For the purposes of this thread let's forget about the fact that dual carbs on a vespa is pretty ridiculous and the more logical option is aftermarket cases. Previous threads already discuss in much depth the differences between one large carb and small ones, and their effects on flow characteristics.

Has anyone here on MA actually personally built and run a dual carb Vespa? I'm talking one rotary valve intake and one reed valve intake on the small half . . . but slight variations are welcome. What was your experience like? Challenges? Outcome? Was it un-tuneable and un-rideable?

Re: Are dual carb Vespas REAL?

Dirty30 Dillon /

I've never seen one running in my travels. Most people running a RV case half are doing so to get one big carb on there, vs. another small one, so they are capping off the stock spigot.

I'd be stoked to see one running and hear some feedback.

I have played with crank rotary, reed valve, Sacre cases, and one of the South American made Rotary valve setups, but never pulled the trigger on the Pinasco dual carb

Re: Are dual carb Vespas REAL?

I am building one this winter using the treats cnc Aluminum reed valve case half. I have some ideas and am just waiting on a couple more parts.

Re: Are dual carb Vespas REAL?

Jason ( ͡° ͜ʖ ͡°) /

> Brian F Wrote:

> -------------------------------------------------------

> I am building one this winter using the treats cnc Aluminum reed valve

> case half. I have some ideas and am just waiting on a couple more

> parts.

Awesome! I hope we can both bring these builds to fruition. My dual carb bravo is a winter build as well. Maybe we can use this thread as a dual carb vespa build thread.

I wish I could have gotten that case half when it was available, but it seems to be no more. I tried on the secondhand market as well. So, the pinasco is all I have. . .. requiring me to source or fab a special crank.

What other specs will your build have? What kind of vespa?

Re: Are dual carb Vespas REAL?

yeah, there was a dude from Wilmington (I think) that had one that he brought to many rallies 2010-2012-ish. Jake I think his name was? I'm sure someone will chime in. It ran pretty good and kept up with group rides fine but wasn't anything earth shattering. I saw that bike at WLR, dead peds, and maybe of our rallies?

If I recall his set up was different than what you're describing. I'm pretty sure it was one rotary case intake and one cylinder intake on what I assume was a bitubo top end both shas, one vespa sha and one "normal" sha

I also saw one at a swap meet in Milan a couple years ago. dude started it up but that was all I really saw of it. Dos guys and Willie treats were there, maybe they remember it better. (edited)

Re: Are dual carb Vespas REAL?

> I wish I could have gotten that case half when it was available, but it

> seems to be no more. I tried on the secondhand market as well. So, the

> pinasco is all I have. . .. requiring me to source or fab a special

> crank.

If you just buy the pinasco case half it comes with a 13mm intake too. The complete dual carb bottom end from them comes with a 19mm intake.

> What other specs will your build have? What kind of vespa?

It's a bravo.

Stock cases + the reed block case half

Kinetic CDI

64cc Polini racing kit

Mazzucchelli crank

Rotary valve intake reamed out to 13mm, 13mm SHA

Reed valve intake w/ malossi 4 petal reed block, 19mm PHBG

Simonini Calibrata exhaust

9.49:1 CIF gear set

Polini variator

MLM water cooled head

Probably a 100mm rear driven pully (I have a pile of rear clutch parts to play with) with a polini spring (edited)

Re: Are dual carb Vespas REAL?

Jason ( ͡° ͜ʖ ͡°) /

Sounds very similar to what I play on running!

Superbravo, Moparts aluminum racing subframe, stock cases, Kinetic CDI 9.49:1 CIF gear set, Polini variator, and also an MLM watercooled head. I've got a lot of wheels to pick from but I'm probably running some cool 10 star mags in the back and some 8 (I believe) star rare plastic polymer wheels in the front (we'll see if they fit). I like how skinny these wheels are. I have yet to find any radiator parts or a pump, etc.

I am going to instead be running the Malossi 43mm, probably stock rear pully and I have some springs I can play with. Mazzy anti special racing crank or potentially a drilled out stock crank with a 13mm hole in it (I haven't measured the crank yet to see if that will work, and I need to do some flow calculations and porting math but I think that's what I'm looking for.

The air inlet on the rotary side is opened up to 13mm like yours, and then like you said the pinasco half is 13mm, I may see about trying to open that up a little and potentially run a different intake that sits on a slightly different angle. I need to inspect the case half when I get it. If I don't modify it I'll run dual SHA carbs probably unless that's un-tuneable. I am unsure on pipe right now. Hopefully by the time this build comes to fruition Cranks can have his vespa pipe done, otherwise I will probably run a calibrata as well or I may modify a huge chamber onto a metrakit pipe I have.

Are you going to thermosiphon with your MLM head? I am opting to run a pump first so I don't have to worry as much about flow and cooling while tuning, but will probably try to upgrade to a siphon setup in the future.

Anyways, @andysimpon it's good to hear you've actually seen one in the wild a few times! I feel like dual carbs or not, vespas are often hard to build for serious speeds. That 50-60 range seems to be incredibly hard to achieve even with dual carbs or huge kits and aftermarket cases. Hopefully someone can chime in on the exact details of that build, would love to hear more.

Re: Are dual carb Vespas REAL?

> Superbravo, Moparts aluminum racing subframe, stock cases, Kinetic CDI

> 9.49:1 CIF gear set, Polini variator, and also an MLM watercooled head.

> I've got a lot of wheels to pick from but I'm probably running some cool

> 10 star mags in the back and some 8 (I believe) star rare plastic

> polymer wheels in the front (we'll see if they fit). I like how skinny

> these wheels are.

That's cool, I only have the stock spoked wheels atm. Moparts has been out of stock of the Al subframes, so I'm going to reinforce the stock one (I have the laser cut plate from treats) as an excuse to teach myself how to weld.

> I have yet to find any radiator parts or a pump, etc.

A lot of folks like dirtbike radiators; a radiator from a CR80 is a common choice, they have lots of mounting points, and they're cheap on ebay.

> The air inlet on the rotary side is opened up to 13mm like yours, and

> then like you said the pinasco half is 13mm, I may see about trying to

> open that up a little and potentially run a different intake that sits

> on a slightly different angle. I need to inspect the case half when I

> get it. If I don't modify it I'll run dual SHA carbs probably unless

> that's un-tuneable. I am unsure on pipe right now. Hopefully by the time

> this build comes to fruition Cranks can have his vespa pipe done,

> otherwise I will probably run a calibrata as well or I may modify a huge

> chamber onto a metrakit pipe I have.

I'm going to start by cheating; I'm planning on having two throttles, one for each carb. Idle will be 99% the SHA, and I'll use that for tooting around, then switch over to the PHBG for go-fastness. I'll play with using them both next year, but this will get the bike moving relatively easily. If I find that I hate it all I can always plug up the rotary valve intake and switch to a full circle crank.

> Are you going to thermosiphon with your MLM head? I am opting to run a

> pump first so I don't have to worry as much about flow and cooling while

> tuning, but will probably try to upgrade to a siphon setup in the

> future.

Thermosiphon for sure. Much simpler and they work great on mopeds.

Re: Are dual carb Vespas REAL?

This weekend some mope showed me some sweet aftermarket cases, throttle splitters, dual 13 SHAs, custom subframe, and fuel line T splitters, but I'm skeptical.

I bet those throttle cables are going to be a wicked mind puzzle when he gets to it.

Re: Are dual carb Vespas REAL?

todd amundson /

> Edward Koipond Wrote:

> -------------------------------------------------------

> This weekend some mope showed me some sweet aftermarket cases, throttle

> splitters, dual 13 SHAs, custom subframe, and fuel line T splitters, but

> I'm skeptical.

>

> I bet those throttle cables are going to be a wicked mind puzzle when he

> gets to it.

The cables for dual carb setups and mopeds is crazy. Lots of soldering tiny ends that go into slides and splitters.

One big issue is if you have a 21mm carb but a splitter that’s only got 18mm of travel, the entire carburetor bore will not be open all the way. If you can find the Domino splitter with a metal slide in it, use it.

I made a splitter from a BMX brake splitter. No slide inside, only three cables soldered together. Maximum throw. Largest carb opening 15mm.

D7A0F549-0E5A-43C2-AFF4-AC62181FE8D0.jpeg

The malossi dual cable splitter will leave you stranded and or stick! Even with the trust of making my own splitter, my dual carb bike has two kill switches on both sides of the bars. Just in case.

B23BC0FB-3CCC-4E1D-8E0B-F1EE33E80B91.jpeg

Re: Are dual carb Vespas REAL?

Pretty clean shop you have^ . ;)

Re: Are dual carb Vespas REAL?

todd amundson /

Funny. Who’s office is that? On the maximum throw comment. Think about this. If you have a 15mm and a 19mm carb, the single cable on top will only open the 15mm carburetor and the 21 will still have like 5-6mm to go but can’t. A one millimeter difference in carburetor bore between the two you can get away with but that’s about it.

The carburetor bores between your two need to be damn near identical.

Re: Are dual carb Vespas REAL?

> todd amundson Wrote:

> -------------------------------------------------------

> Funny. Who’s office is that? On the maximum throw comment. Think about

> this. If you have a 15mm and a 19mm carb, the single cable on top will

> only open the 15mm carburetor and the 21 will still have like 5-6mm to

> go but can’t. A one millimeter difference in carburetor bore between the

> two you can get away with but that’s about it.

>

> The carburetor bores between your two need to be damn near identical.

There is a way around that , but , it would likely require a lever with offset pivot on the larger carb .

I'd imagine tuning would be very interesting .

Re: Are dual carb Vespas REAL?

Dirty30 Dillon /

> P D Wrote:

> -------------------------------------------------------

> > todd amundson Wrote:

>

> > -------------------------------------------------------

>

> > Funny. Who’s office is that? On the maximum throw comment. Think about

>

> > this. If you have a 15mm and a 19mm carb, the single cable on top will

>

> > only open the 15mm carburetor and the 21 will still have like 5-6mm to

>

> > go but can’t. A one millimeter difference in carburetor bore between

> the

>

> > two you can get away with but that’s about it.

>

> >

>

> > The carburetor bores between your two need to be damn near identical.

>

> There is a way around that , but , it would likely require a lever with

> offset pivot on the larger carb .

>

> I'd imagine tuning would be very interesting .

Easy way to coincide required throw for differing bores is to mount the cables on a cam, a la the splitter on the Champ. Two different throws, one for carb one for oil injection, mounted on a cam.

In reality, tuning two carbs with two different types of induction is hard enough, forget adding that one is a SHA and the other is a multi-circuit. Your best bet is using a 1:1 pull, but than offsetting the cable on the SHA and running it through reduction so it only opens at the 3/4 - WOT positions of the other carb to act like a powerjet.

I would stick with dual SHA's all the way.

Re: Are dual carb Vespas REAL?

Some carbs have more over travel than others, you could always cut down the top of the slide a couple mm.

Lots of dirtbikes have splitter cables, usually when I need one I just buy a cheap one for like a polaris 2t quad or something that's gonna be hella long and cut it down. I think I used a 90s polaris 2t quad for my dt250 cable and it was easy peasy

Re: Are dual carb Vespas REAL?

You could leave some slack on the smaller carb so it opens later like a secondary barrel on an automotive carb

Re: Are dual carb Vespas REAL?

Jason ( ͡° ͜ʖ ͡°) /

Hahahaha hi Eddie. All this speculation and problem solving over throttle pull length . . . I'm running two identical 13mm SHA carbs (or at least that's the plan right now) so this will not be a problem for me. I did order one of the CNC halves that Tyler linked to in my WTB thread. If this build goes well I may do the dual carb dirty deed on my grande as well . . . but use a much bigger carb on the small half. The pinasco limits you to an 11mm hole in the small side of the crank. So IMO anything much higher than a 13mm carb is largely useless. Similar to the restriction on the stock spigot (but hey at least you have two of them on a dual carb setup). But, the CNC halve shoots right up in front the bearing/crank altogether so you can go pretty big on that carb. I was thinking of potentially pairing that with the new 46mm malossi and stock cases cut with their purpose built cutter. But that's all later on, maybe.

Brian said he is hooking the throttle for his separate carb up entirely separate, kinda suicide style I guess? Smash on the NOS at full throttle kinda style maybe?

Whoever mentioned malossi throttle splitter leaving you stranded . . . the one that came with the pinasco seems to be really good quality. I don't really see it being likely to fail. The little cam/slider fits nicely in the sleeve and it seems to be machined well for normal sized throttle cables. Yeah some soldering will be required but that's all fun. However I could see it being cool to just have a hard soldered Y shaped throttle. It may prove to make the sleeving and routing challenging but maybe even less of a chance of failure.

I've attached some pics of the splitter, I think it's really damn cool. And a pic of the engine mocked up kinda, just for fun. Was considering making a separate build thread but I think I'll just keep updating this one and encourage other dual carb vespa peeps to post their progress as well.

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Re: Are dual carb Vespas REAL?

Jason ( ͡° ͜ʖ ͡°) /

I think this will be a really fun project. This is personally the most "all in" I've gone on a moped since I started back up with them over a year ago. I'm so excited to see this thing come together.

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Re: Are dual carb Vespas REAL?

Just run one twist throttle, one trigger throttle like on Gopeds.

Or all you bukakke dudes are already used to the physical action of double twist throttles , so jack those pins bro

Re: Are dual carb Vespas REAL?

🇮🇹💦 Of the Loin /

Only if Birds are

Re: Are dual carb Vespas REAL?

I was taking a look at how my XL600 uses the dual carbs on a single cylinder, only one carb has an idle circuit, and at idle the one without is closed off totally. Only once you open up the throttle like maybe 1/4 of the way does the auxiliary carb open up.

Obviously a 600cc single cylinder 4 stroke with 2 carbs is a lot different than this application though

Re: Are dual carb Vespas REAL?

Tweaker trash /

The easiest thing to do is to talk to someone with an e50 dual intake and see if there was any big difference in performance

https://www.dimecitycycles.com/honda-2-into-1-throttle-cable-fits-cb350-cl350-s.html?gclid=CjwKCAiA_eb-BRB2EiwAGBnXXtS2qdhBC4BeKl-AY-Dku97ndAu4jn1gYjqExdU7qqYNa7N60JXzNBoC6pgQAvD_BwE

Re: Are dual carb Vespas REAL?

Jason ( ͡° ͜ʖ ͡°) /

Easiest thing you can do to figure out what?

I think dual intake into the same port is a different situation here performance wise because it's effectively very similar to just adding a bigger carb at that same location. Are you talking about the Y shaped intakes? With 1 set of reeds? I feel like dual carbs on separate intakes in different locations of the crank case, both using different types of induction, is quite different and probably much more challenging to tune.

That throttle cable looks like and uses a very similar mechanism to the one that came with my pinasco kit. The knarps are huge and would need some grinding/modification but I think I may just pick one of those up just in case. Thank you!

Re: Are dual carb Vespas REAL?

Jason ( ͡° ͜ʖ ͡°) /

@Nick That's pretty cool. Besides the carbs being different do you know how it's managing opening the second carb at 1/4 throttle?

I know one possibility is definitely by messing with cable slack and cable adjusters on the throttles and carbs to adjust the timing. The larger challenge tho would be to change the RATE at which one of the throttles opens. Does that second throttle cable actually pull at a faster rate?

Like someone mentioned above I guess you'd be looking at some kind of exponential pulley system. (edited)

Re: Are dual carb Vespas REAL?

What I don’t understand is why you wouldn’t want control over each carb individually.

Snordly ran a double carb setup with individual throttle control on an e50 during pinball with a 16mm case reed and 24mm piston port. So fucking fast.

I guess I’m just lost on why people don’t mod Vespa cases for big reeds. I know there’s not much room but surely there’s enough to cram a 24mm ID aluminum tube into the cases and weld it in somewhere, then use a separate stand alone reed block

Re: Are dual carb Vespas REAL?

> Jason ( ͡° ͜ʖ ͡°) Wrote:

> -------------------------------------------------------

> @Nick That's pretty cool. Besides the carbs being different do you know

> how it's managing opening the second carb at 1/4 throttle?

>

> I know one possibility is definitely by messing with cable slack and

> cable adjusters on the throttles and carbs to adjust the timing. The

> larger challenge tho would be to change the RATE at which one of the

> throttles opens. Does that second throttle cable actually pull at a

> faster rate?

>

> Like someone mentioned above I guess you'd be looking at some kind of

> exponential pulley system.

So on the Honda setup the carbs are next to each other like it's a twin cylinder bike, or a 4 cylinder (CB350/550/650/750F) but it only has one set of throttle cables for the one carb. So it just has a linkage running from one of the carbs to the other one

Re: Are dual carb Vespas REAL?

Dirty30 Dillon /

> JBOT Admin Wrote:

> -------------------------------------------------------

> What I don’t understand is why you wouldn’t want control over each carb

> individually.

>

> Snordly ran a double carb setup with individual throttle control on an

> e50 during pinball with a 16mm case reed and 24mm piston port. So

> fucking fast.

>

> I guess I’m just lost on why people don’t mod Vespa cases for big reeds.

> I know there’s not much room but surely there’s enough to cram a 24mm ID

> aluminum tube into the cases and weld it in somewhere, then use a

> separate stand alone reed block

Modding stock cases for big reeds is hard, because the easiest access, RH small case half, still has to be able to fit in the sub, so just welding on stuff is hard, gotta be modular.

Other than that, the euro kids have been building rotary valve and AM6+ sized reed cases for these bikes for years, it's just a lot of work for a bike that has been pretty mal-aligned by the majority of the US moped community.

I couldn't count how many times I read negative comments on Vespa bikes when I was getting into things like 8 -9 years ago. Lo and behold, they are pretty much all I jam on now.

Re: Are dual carb Vespas REAL?

I’ll get to mine eventually. Was waiting to get a tig to mod the cases then the project got sidetracked. Hopefully this coming spring?

I also always wondered why no one modded their frame to have a bolt on modular section that could be removed and reinstalled easily for engine removal and welded case fuckery

Re: Are dual carb Vespas REAL?

Dirty30 Dillon /

> JBOT Admin Wrote:

> -------------------------------------------------------

> I’ll get to mine eventually. Was waiting to get a tig to mod the cases

> then the project got sidetracked. Hopefully this coming spring?

>

> I also always wondered why no one modded their frame to have a bolt on

> modular section that could be removed and reinstalled easily for engine

> removal and welded case fuckery

The last couple aftermarket/small batch subs all feature this, to make fucking with RH intake/reeds, and RH ignitions on the Sacre style cases easier.

The stock subframes already have so many issues with strength, it would definitely compromise it/require enough additional mods on a stock subframe to validate just fabbing a new solution.

Although I DO love the idea of just a drop section... been trying to think of a decent way to modify my aftermarket sub for easily installing my Sacre cases with the RH ignition.

Re: Are dual carb Vespas REAL?

Not these would work without a bit of innovative intake design , but , here's a dual carb setup that is stock on my XT350 ( a single cylinder motor ) .

They are kind of a strange brew .

The primary is mechanical lift , for that low end torque , and the secondary is a CV with a diaphragm to aid in the higher RPMs .

(edited)

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