Modern Vespa

Hi Guys.

I have been talking to people and reading threads on the mixture screw that are conflicting. Some people say out is richer some people say in is richer. I have the spaco so 26/26 can anyone confirm wich way.

Many thanks Matt

What does richer mean?😄

IN to weaken (reduce flow of mixture), OUT to richen (increase flow of mixture). Go IN too far, consider a weaker idle jet, and go OUT too far, consider a richer idle jet. On a Spaco, the accepted sweet spot is 2.5 turns out

Are there different variations in the spaco ? I have a 20/20 Spaco 20d carb, the idle jet is a 50-120, and I'm out about 1-3/4 turns. Perhaps I should be using a different idle jet? Just starting to tune carb.

Lynn, that's pretty good if it's running well. That's quite a rich idle jet, and you are on the verge of needing a leaner one. (All?) Spaco carbs have a fine screw pitch, hence the 2.5 turns sweet spot. The older/original Dellorto was ~1.5 turns OUT.

Can I possibly have old stock ? I haven't done anything with the mixture screw or jet.

Many thanks

Look at the threading. It's M5 x 0.50mm for the new and M5 x 0.75mm for the old mixture screws.

For comparison, a "standard" M3 bolt is a 0.50mm pitch and an M6 is 0.70, so you can eyeball your mixture screw against those if you're not sure.

Also, SIP published a good si carb tuning guide once upon a time, but the link seems to have died with their web site migration, so here's a link to my personal copy.

(I'm fighting with the idle on my GL right now, so I'm also refreshing on a lot of this stuff. )

Hey thanks Chandler through my many searches I kept coming across the Sip link and it was a dead end on their end , much appreciated for sharing your copy. I will pull the mixture screw sounds like it's going to be pretty obvious. I have my old 20/17 carb here as well I'm going to take a look at, so much to learn and even once we learn it , difficult to retain for latter use. Growing old sucks.

I had to replace my original Dellorto SI 20/20 with a SPACO 20/20, which I bought from SIP; and tried to swap all the jetting from the original carb to the SPACO, with the usual recommendation of the 2 and 1/2 turns out on the mixture screw.
The result was bog down from idle, and a big flat spot in midrange. It also had a tendency to flood. Any other in or out settings (from 1 to 4 turns out) of the screw made running way worse.
Once I replaced my jets with the ones that came on the SPACO, I reverted to the 1 and 1/2 turns out as SIP states that is" the ideal position" and the start of adjustments as a reference point. And that is the way it has been since.
Engine idles perfect, no more bogging or flat spots.
I think the carb casting on the SPACO has been drilled and tapped for the same mixture screw travel as the original screw and thread pitch.