Vespa Sha carb tuning with slides.

Chris Carleton /

Are they sold for the Vespa Sha? My Ciao is really rich off idle takes several seconds to clear it out.How bout a slight bevel on bottom of slide?Thoughts on this anyone?

Re: Vespa Sha carb tuning with slides.

I file 2 small notches in the bottom of my slides on both sides of the emulsion tube. It seems to help with the rich idle, mid throttle.

Re: Vespa Sha carb tuning with slides.

Re: Vespa Sha carb tuning with slides.

> - Joe - Wrote:

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

> Here’s a previous thread about it.

>

> https://www.mopedarmy.com/forums/read.php?7,2891329,2895993#msg-2895993

Serious question, not a troll. I've read that whole thread as well.

Why would that work? Wouldn't it just result in a higher idle? Wouldn't adjusting the idle screw be the exact same result?

Re: Vespa Sha carb tuning with slides.

Re: Vespa Sha carb tuning with slides.

Too bad the vespa sha uses a different slide.

Re: Vespa Sha carb tuning with slides.

> Ike Pipe Wrote:

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

> > - Joe - Wrote:

>

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

>

> > Here’s a previous thread about it.

>

> >

>

> >

> https://www.mopedarmy.com/forums/read.php?7,2891329,2895993#msg-2895993

>

> Serious question, not a troll. I've read that whole thread as well.

>

> Why would that work? Wouldn't it just result in a higher idle? Wouldn't

> adjusting the idle screw be the exact same result?

It would be higher idle you would need to readjust. But with the notches it allows more air to pass through while still covering the fuel hole in the emulsion tube. It seems to work well on my bikes running a 12.12 or 13.13 carb.

580C89FE-0478-47FE-A9C0-8C0F9D0D665D.jpeg

Re: Vespa Sha carb tuning with slides.

Dirty30 Dillon /

The reason it isn't the same as raising you idle is that you are introducing a fraction of the air compared to if you raised the whole slide. The key is to just add a little eddying air to lean the off-idle so you don't have any bog.

I have used this on non-vespa's alot. Typically I find this moot on Vespas as I would just clutch the bike into the pipe, thus avoiding the low bog.

Re: Vespa Sha carb tuning with slides.

^ this

the other factor is slide cutaway, the amount of bevel on the bottom of the slide

a flat-bottom slide will be the richest low-part throttle, the more slanted bottoms are more progressive.

its pretty easy to mod them with a file or a sander to change, even a dremel round sanding drum will let you add a curve and get weird.

Re: Vespa Sha carb tuning with slides.

Very interesting. I've read bunches of threads that talked about it, but not often does it mention exactly why it should work.

I've tried beveling the bottom of the slide, but haven't yet tried the notches.

Re: Vespa Sha carb tuning with slides.

i think the size of the carb matters too. 12:9 vs 12:12 etc. by i like to knife edge mine.

Re: Vespa Sha carb tuning with slides.

it lowers the velocity of the air at the emulsion tube at part throttle so you don't get as much vacuum.

when the slide is all the way up, the cutaway no longer matters because its out of the way and the main jet fuel delivery is the same

its most effective from like 0 throttle to about 1/3 throttle on an SHA but it still has some effect all the way up to about 3/4 throttle

its a very very useful mod, if you read the mikuni handbook that explains it pretty well, but obviously it behaves differently on a single jet SHA than a multi-jet VM

once you see how big of a difference it makes you'll cut the slide more or less in every SHA bike you own

Re: Vespa Sha carb tuning with slides.

Its no secret that different sha slides were offered to tune idle, low end and into the midrange.

dellorto-SHA-slide-metal-4T.jpg

Re: Vespa Sha carb tuning with slides.

Easy to miss this tuning sha but pretty important. Yeah Graham nailed it. I never really noticed until I started playing with it and it makes noticeable and predictable change, totally legit

Re: Vespa Sha carb tuning with slides.

Glad this got brought up again, heres a puzzle:

When I first start her up in the morn, I get that growly 4 stroking sound at the low end, but I dont get that sound or feel after a mile or so.

Ive beveled a #2 slide to nearly a #4 but still get that growly sound just not as long.

Think these little cutouts would help?

Also! I got one of those Sooper Dooper 3d printed slides, and even with the idle screw all the way out, the idle is crazy high, as soon as i gave it gas, it was four stroking? So i took it out and now its just sitting around.

Re: Vespa Sha carb tuning with slides.

sounds like your plug is too cold, try going down a number or two.

if you have low compression a b5 or a b6 is fine.

the other thing with a vespa it could be a leaky decomp? basically anything that causes it to misfire or have low compression until it heats up, tired rings, etc.

Re: Vespa Sha carb tuning with slides.

> . Chudas. Wrote:

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

> Glad this got brought up again, heres a puzzle:

>

> When I first start her up in the morn, I get that growly 4 stroking

> sound at the low end, but I dont get that sound or feel after a mile or

> so.

>

> Ive beveled a #2 slide to nearly a #4 but still get that growly sound

> just not as long.

>

> Think these little cutouts would help?

>

> Also! I got one of those Sooper Dooper 3d printed slides, and even with

> the idle screw all the way out, the idle is crazy high, as soon as i

> gave it gas, it was four stroking? So i took it out and now its just

> sitting around.

I'll buy that 3D slide if you dont want it. Lmk

Re: Vespa Sha carb tuning with slides.

Dirty30 Dillon /

Just for clarification, the 3D printed slide is not for Vespa.

Re: Vespa Sha carb tuning with slides.

> Dirty30 Dillon Wrote:

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

> Just for clarification, the 3D printed slide is not for Vespa.

Yep, vespa sha carbs use different parts(edited)

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account