Modern Vespa

It' not hard to machine in a step, but then you also have the manufacturing variability of the carb. If it was the same level then flat is flat. Looks like only a mm or 2 max, I may order one and see if I can mill it down.

I can't take credit for the replaceable seat idea, was mentioned in another thread around here. Shocked it's still not been done.

Just bumping this thread up again, on the subject of alternate ways to have a bellmouth intake on the carb *and* have air filtration *and* keep the air bellow. Bonus points for simplicity, and ease of cleaning.

Here's what I've come up with -- see attached.

See, I found a bunch of filters for old velocity stacks that might just snap on to the PX air box. (57-58mm diameter or thereabouts.) Then, so goes my thinking, the air bellow could be stretched over top of that, and bob's your uncle.

http://www.carburetion.com/Products/ProductDetails.aspx?part=CUSF57LP

http://www.mikunioz.com/shop/velocity-stack-with-gauze-fits-carburetor-spigot-58mm-thru-62mm/

https://www.merlinmotorsport.co.uk/p/weber-40-dcoe-mesh-ram-pipe-filters-pair-afm4056

http://www.bisonmotorsports.com/Push-In-Microphone-Filter-for-Bison-Motorsports-Ve-p/00-0057.htm

Whaddya think?

I have plenty of trouble getting the bellows over the carb box lip as it is (unless I do that end first, and then the trouble is at the other end!) so I'm not sure how well that would work... it could be fitted inside the hole (50mm diameter). But you still end up with a kind of non-filtering filter...

I like what a friend did on his. Just needs some kind of plate to keep it in place (2nd pic) - and a good tank removal/replacement technique!

Ginch -- yeah, I saw that one, and it's ingenious, but it looks like a bitch to clean (as you point out.) I wouldn't want to have to pull the tank every time.

"But you still end up with a kind of non-filtering filter... " -- what do you mean? A few of of these filters have a *lot* of mesh to them. More than what's on the stock air filter, at any rate.

Have you seen the "Dumbo" from MRP??

https://www.mrp-racing.de/Air-hose-adapter-50mm-DUMBO-Vespa-PX-T5-Sprint-Rally-VNB

I haven't, but that's fascinating.

What does it achieve, other than allowing other air bellows to be clamped to the frame?

Maybe an inline filter could be installed on the end of it? Given the different clamping mechanism that would get around the trickiness of squeezing the stock air bellow over it.

EDIT: I see now that this Jumbo doodad was in answer to Ginch's question about having a secure mount for that polini foam filter mounted on the inside of the frame.

That Dumbo thing is a bit strange... looks like too much hardware for the issue at hand.
I wonder if you could find or make a conical-shaped foam filter that clips in to the body hole from outside?

I think a flat foam filter between the 2 plates would do the trick and it would be easy to clean...

I considered fitting a filter at the opening under the seat, still think that could be a good idea.

oopsclunkthud -- me too. I bought that LML filter that goes in the hole there, but it looks very restrictive. And I've heard from more than one person that that's the case. The other thing that's worrying about relying on the underseat filter is that there are some holes elsewhere in the frame where dust and crap can sneak in, specifically the slots for the sidepanel latches.

Got a question here about the flow of air however, if I do try putting a filter at the opening of the airbox. Considering the whole point of this exercise is to maximize the efficiency of the bellmouth intake on the carb, would it not make sense to put the filtration as far from the business end as possible (i.e. in the frame)? Or am I thinking too much?

Yup, the further it is away the larger the plenum volume, but the more opportunity for other dirt to find its way in. That's where I was trying to get a good balance with the filter at the gasket layer of the air box. also considered a tapered cone shape filter inside the bellows.

Patrick,

Any chance you have an STL file of the 24 velocity stack I could try out? I'm at my brothers house with a 3D printer.

I don't remember if this is a business for you. If it is, sorry for the ask.

Dave Reed
Slugrockets SC

Unless you are driving on dirt - don't you think the air coming from the frame is relatively clean ? DO you think a filter is really necessary ? I dont bother on one scoot and seems find over a year later...

I think any particle that could really cause damage is too heavy to make it into the carb. In all the twists and turns on the way there it will precipitate out. The light fluffy stuff that makes it just get s incinerated. I have NOT seen any evidence of much (any at all really ) dirt making it there in the hose near the carb.

email sent regarding the stl file.

I ran the filter in addition to the stock filter last year on the Melee and took the bike on several dirt roads. I did see a good bit of dust from the back of the carb box where I didn't have the rubber plug over the idle mix screw. Saw no evidence of dirt making its way through the frame to the air box.

The filter is still not a bad idea but not convinced it's really needed.

another alternative for the 19mm

adding the template for the large frame filter

Have about 200 miles on my rebuilt V90 motor with Pinasco crank and 100 Sport top end.
19/19 with 80 main, 42 idle, 60 choke and air screw 1 ½ turns out. Proma pipe. Uni 4245 filter. Filter has a spring inside so it fits the limited space in the frame.
Started with an 82 main but couldn't get it running right between ¼ and ¾ throttle.
Now pulls well thru the whole range. Plug looks good.

After over 5yr of overheating struggles with Speedy, Ive decided its about time to consider taking other drastic measures... & taking off the PHBH28 !!

Being me, there no chance I'll (as of yet) just go & get the simple option of a 24/24, and as Ive got a kinda-26/26 (so Ginchi says... "its not really 26mm!"), plus i may be able to find/build a 27/23 off a SS180.
This got me a thunkin; i see that Patrick has made a cool foam filter which fits into the base of the box (so the original air cleaner box & flexi hose that goes into/under the fuel tank), BUT thinking about it (too much) the current setup on Speedy is simply an elbow bolted to engine case & hose to the PHBH, with home-sewn high-flow filter, & it works, then what's the use/point/justification of the air cleaner box? I'll be fitting a vortex or bellmouh to it, & it's likely that would be higher than the cover, so it would be sticking out anyway.
There is no auto-lube , so no channels in the cases, just a goddam big hole thru the cases..

YES, I've used the SEARCH function & still can't find references to not using an air cleaner box, but using a SI carb...
what am i not considering?
What have i missed?
Why does noone appear to be doing this (what i considered simple & obvious) mod?
Theres not even a "need" to make up some fancy adaptor plate if using a SI, its more jist getting out ol' trusty Master Grinder & cutting off everything besides the mounting area.

Ohh... does anyone know what is required to fit the 27/23?
There are 3 bolts to hold it down, so some redrilling/cutting/modification will be required.. (do i REALLY want to cut up a SS carb, just to see if it will work though?)
Another somewhat obvious mod that noone seems to do.

way back I cut down an airbox to keep the oil injection and fited the manifold you have now on top of that and then a phbh.


but more to the point, cutting the airbox to keep only the cable and base would be easy. could maybe find/make/modify the carb to take the cable directly, lowering the carb by ~5mm.

Then an airbox could be mounted on top of the carb with lots of room and a bell, and fed from the frame. Then a filter leading into the frame would keep it all clean. all very GS/SS like

If you don't have an oil pump, the carb box does seem to take up a lot of unnecessary space.

I'm guessing the original design intent behind having the carburetor enclosed in its own little housing may have been (1) to keep the noise down, (2) to keep it from slobbering 2T all over the place, and (3) to feed the carb cooler air from inside the frame. The last was probably the main issue.

Plenty of people run carbs with different filters. I say give it a go without the box. What's the worst that could happen?

I've been pondering a similar move.
Use base of airbox carved out for base.
Then create an airbag that gives the bellmouth plenty of space.

I have two ideas i've been pondering.
One was to use a GS airbag (report - settle down y'all).
I love the large mouth on these.
Polished aluminum looks so nice as well.

But at $130, for a non aluminum painted one, it seems like a lot to go hacking on.

So I have a second concept.
Havent sorted all the details but it is simpler and would also have a classic appeal.

Haven't fully worked it out - but you get the concept.

Just came across this prototype airbox from VMC... seems to be a relevant place to put this info!

https://www.facebook.com/reel/1092694281418368

The VMC airbox is now available.
https://www.facebook.com/permalink.php?story_fbid=pfbid0ZEknNKDCu9MnULdnwoUKYDuisXXGcButV9boyHxCcRB1r4S5eCiMAyZkAHfhXBUXl&id=100057568474363

more...

And at a reasonable price too.

I see they're recommending going up 5-10 points on the MJ with this rig. That sounds like a whole lotta air.

I do like that they have a foam filter slot on this thing.

Here's one: how many bolts does a person have to undo to change a jet? Maybe the top and bottom just come off as a unit and it's a two-bolt process. Would be nice.

They released their radial caliper bracket thingy recently and I saw it was promoted - like this - as a discount price. Their sales are through Avotecnica, and they won't send to Australia. I did ask them directly on FB and they just wouldn't. They said soon it would be available at SIP, and I thought so much for the discount. But it turned out to be something like 25 euros cheaper! And also a reasonable price to begin with.

So maybe this will also be cheaper than that price mentioned. The Polini bellmouth comes (or at least used to come) with something like a 140 main jet. So maybe 15-20 points up. Flow more air, need more fuel.

Gorgeous air box.

I've got mine ordered, and it'll be spirited over into this non-EU fringe of Europe within a week or two. One early adopter of this VMC airbox said when he installed a 148, even that was too lean. Yowsa. Methinks I'll be starting the jetting odyssey with the smallest air corrector I can get my hands on. That, and using the finer of the two air filters the thing ships with.

Installation video.
Pain in the A.

Imagine jetting that thing.
Or just adjusting idle speed

Forget that! I'll stick with Patrick's sweet venturi design. I've got one on both my 24/24 carbs and they work nice!

https://www.shapeways.com/product/CNUFQJZ6D/bellmouth-si24e

Hey now, the jury's still out on that. I haven't installed mine yet, but I've looked it over pretty thoroughly and about the only thing that looks like a full PITA is the hex-headed screw in the still here (which in the original airbox lid also involves an ungainly, head-chewing angle, as we all know, though it's usually Phillips.)

Maybe a Danny DeVito-proportioned hex driver would make it less of a chore to get at. I don't want to have to undo and tighten these things 3/8ths a turn at a time with a traditional Allen key.

Anyhow, it's just two screws out to get at the jets. The whole unit, top and bottom, stays bolted together and just lifts away.

The idle screw meantime is accessed via that big plug screw you can see in the video. I imagine you have to do some blind poking around with your flathead screwdriver before hitting paydirt.

More news after I actually install it (and fix a bunch of other crap while I'm at it.)

Also interesting about this airbox: it ships with pretty conservative-looking brakes on the air correctors and the oval. 5mm for the ACs, 6mm for the oval chimney. Will be interesting to see how it is to jet. The documentation suggests going down to maximum 140AC.

[/img]

In their defense, at least they didn't try to make it look easy!

Yes, jetting could be a pain for sure. I guess there are a lot of people out there who never play around with their jetting though... and this is a very neat solution once it's mounted.
I wonder if you could just fit the bottom half for jetting testing?

I really really like that you can mount the intake hose before the box, getting that on normally I find to be a real pain.

Looks like the idle screw is pretty easy once you take the plug out.
I would have liked to see the same size head on all the screws on top so you don't need to carry a full set of allen keys... maybe a rubber plug for the idle would have been a better option.

Jim's idea of the stubby driver is a good one. Looking forward to seeing your comments when you mount it.


I wonder how it performs vs a Polini or Patrick's venturi?

I've bought the radial caliper mount for my next scooter project, it's not a bad looking piece of gear, it's just a cast piece of alloy so not as nicely finished as a CNC piece but will still do the job and would fit in nicely with a stock type of build.

Me too. The casting is not... beautiful... but looks up to the job. And was heaps cheaper than AF Parts or the other options.

Picts... might be a while before it's on a scooter though

I want one of these, those gorgeous Italian castings should polish nicely! They currently are discounted to 115 euros from 130 here https://avotecnica.com/nuovi-prodotti/3551-air-box-vmc-venturi-per-vespa-large-frame-125150200-.html

I guess that chart proves it. Red is definitely faster!

Shapeways has free shipping on orders placed today

Single-Use Code: 2024FREESHIP

https://www.shapeways.com/shops/oopsclunkthud