vespa carb jetting

XBrandon EdgeX /

does anyone know the jet size increments on vespa (dellorto carb) jets? EX. on a puch (bing carb) it goes in increments of 5 (55,60,65, etc). Does the vespa go every number, or every even number or something?

Thanks,

Brandon

Swarm and Destroy

Re: vespa carb jetting

Im not positive , but i think its odd #'s (39, 41, 43, 45, 47, etc)

I finally got through to Vespa supershop today and these were the jet sizes he named to me.

Re: vespa carb jetting

XBrandon EdgeX /

Cool. Thanks, John.

Re: vespa carb jetting

There's also a 49, which is the biggest stock jet for Vespa Grandes.

Jim

Re: vespa carb jetting

The Ciao originally came with a #43 jet. Very late models of the Ciao came with a #49. The Grande carb came stock with a 49, as it had a slightly larger carb, freer flowing airbox, and larger induction chamber in the otherwise identical engine. I also have a #50 in a spare dell'Orto carb, so they go at least that large. FYI, I've tried swapping jets and it requires some fooling around with the airbox also. Just replacing the jet with a larger one doesn't seem to work, as the mix ends up too rich.

Chris

Re: vespa carb jetting

XBrandon EdgeX /

Yeah, I know that just changing the jet isn't gonna give it any better performance, but I'm gonna put a performance exhaust on it, and they usually end up leaning the engine out a little bit, so I need to know what size jets are available.

Re: vespa carb jetting

I own 2 ciaos, a 78 and a 79. The jet on the 78 is a .43, on the 79 its a .45. I swapped them to see what kind of difference it would make. ( I should add here that I had 2 of the 3 holes plugged on the air box of the 79, It seemed like it was 4 stroking and plugging the holes fixed it in a snap.) With the .43 jet in the 79 (instead of the .45) it has better acceleration, but top speed stayed the same, and it runs like a champ without the plugged holes. Then I ran it without the air box at all, same deal, even better acceleration but no change in top speed. I replaced the airbox for the time being (to prevent any airborne particles from entering the engine), but am considering either replacing it with the 6 holed Grande air box, or just drilling some more holes in my ciao airbox to increase air flow. On tuesday my .41 and .39 jets should come in (hopefully), and I will let you know what kind of difference (if any) it makes. Brandon, does this help you at all? And where did you find a performance pipe? What brand is it? How much did it cost?

Re: vespa carb jetting

XBrandon EdgeX /

I haven't gotten a pipe yet, I'm still looking around for one. I just wanted to know what size jets were available so it wouldn't be searching blindly for jets. Often times, places will say "all sizes available" and I don't know what to ask for.

I should have phrased that "I hope to put a pipe on it" :) If I can't find one, I'll probably build a straight header for it, or maybe use that javapipe thing if I can figure it out:

http://beadec1.ea.bs.dlr.de/airfoils/tpipedes.htm

Re: vespa carb jetting

look at the one that is in it .. then buy the next 2 or 3 bigger jets they offer for it

(i.e. .. if you already have a 58.. buy a 60 and a 62 and a 64... or whatever they are)

There is no 'set' jet for any bike or combination.. you have to test it and change.

Re: vespa carb jetting

Brandon and Vespalad,

Here's a good one. I have two Grandes sitting here. One has the 49 jet in it and the 6 hole airbox and it runs like a champ. The other has the same 49 jet, but has the standard 3 hole airbox and it leans out and 4 strokes. I can't seem to figure out why. Fuel line runs free and clear, carb and jet are clean. I'm stumped. Regarding the performance pipe, let us know what you find. I have a Sito knock-off on mine. It is pretty loud, but added 6 mph to my top end. I'm still running the normal jet (49), but am considering playing with it by putting a 50 in that I have laying around. I'll report back after I get a chance to try.

Chris

Re: vespa carb jetting

Chris, how much difference in size is there between the 2 airboxes? I am probably going to drill some more holes in my Ciao box to let more air in, instead of getting the Grande box. But I've never seen the Grande box, maybe it would be a better idea to just get one of those. What do you think?

Re: vespa carb jetting

XBrandon EdgeX /

Sounds like it might be a vaccum leak somewhere. Spray some carb cleaner or starting fluid on the joint between the engine and the carb while the bike is running. If the engine speed changes or sounds different, you've got a vaccum leak. Try putting some teflon tape or gasket maker around the tube that the carburator slides onto. Also, make sure the airscreen is intact.

Re: Air Boxes

The air boxes are all the same. The disc that sits behind the filter screen (away from the engine) has the holes. Three for the smaller carbs and jets, six for the larger.

The smaller carb has a 10MM throat, the large is 12MM.

How to spot them in a glance:

On a 10MM, with the choke blade in the open position, there will be a space between the edge of the blade and the edge of the throat.

On the 12MM, the edge of the blade is almost touching the edge of the hole.

Hop up tip that probably doesn't work:

On my Grande I noticed that the outside end of the throat had a sharp edge on it. I sanded it round with some emery cloth, them polished it with white rubbing compound. A poor man's velocity stack! If you try this, don't reshape the throat. just round off the sharp edge.

I think this is the equivalent of disconnecting the governor on mine.

Jim

Re: vespa carb jetting

Ron Brown /

Chris,

4 stroking is caused by running too rich. The air box with fewer holes is creating a slight vacuum at the carburetor and sucking too much gas.

If you can, verify this by swapping air boxes, or try running without the 3 holer to see if it improves.

Ron

Re: vespa carb jetting

Vespalad,

There is absolutely no difference in size between the two boxes. The 6 holes vs. 3 holes I've been mentioning are in the plastic just behind the filter screen. The outside three holes (tubes) on the top are the same for both boxes. I have four of these air boxes (two of each) and all are slightly different in design. On some, the part I've described is integrated into the box molding. On others, it is a removable piece. The only difference is in the number of internal holes. No more air gets into the box since the outside holes are the same. The difference is that the air inside the box is freer flowing and probably enters the box faster. The other major difference in the carbs is that the Ciao is a 10 mm carb (dellorto 12.10) and the Grande is a 12 mm (dellorto 12.12). On the 12.10, the brass fuel tube has two small holes in it, on the 12.12, there is one larger one. I hope this description is clear. If not, I could probably scan the six hole version and post it.

Chris

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