Mon Jun 07, 2021 10:27 pm

Member
Motovespa 150s lambretta li150
Joined: 07 May 2021
Posts: 38
Location: uk
 
Member
Motovespa 150s lambretta li150
Joined: 07 May 2021
Posts: 38
Location: uk
Mon Jun 07, 2021 10:27 pm linkquote
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
Mon Jun 07, 2021 10:43 pm

Molto Verboso
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: 16 Apr 2011
Posts: 1875
Location: Siam
 
Molto Verboso
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: 16 Apr 2011
Posts: 1875
Location: Siam
Mon Jun 07, 2021 10:43 pm linkquote
What does richer mean?😄
Mon Jun 07, 2021 11:47 pm

Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1754
Location: UK (South East)
 
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1754
Location: UK (South East)
Mon Jun 07, 2021 11:47 pm linkquote
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
Tue Jun 08, 2021 12:07 am

Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2516

 
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2516

Tue Jun 08, 2021 12:07 am linkquote
swa45 wrote:
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.







Last edited by Lynnb on Tue Jun 08, 2021 12:25 am; edited 1 time in total
Tue Jun 08, 2021 12:19 am

Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1754
Location: UK (South East)
 
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1754
Location: UK (South East)
Tue Jun 08, 2021 12:19 am linkquote
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.
Tue Jun 08, 2021 12:27 am

Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2516

 
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2516

Tue Jun 08, 2021 12:27 am linkquote
swa45 wrote:
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.
Tue Jun 08, 2021 2:43 am

Member
Motovespa 150s lambretta li150
Joined: 07 May 2021
Posts: 38
Location: uk
 
Member
Motovespa 150s lambretta li150
Joined: 07 May 2021
Posts: 38
Location: uk
Tue Jun 08, 2021 2:43 am linkquote
Many thanks
Tue Jun 08, 2021 3:22 am

Ossessionato
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 3775
Location: Nashville
 
Ossessionato
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 3775
Location: Nashville
Tue Jun 08, 2021 3:22 am linkquote
Lynnb wrote:
Can I possibly have old stock ? I haven't done anything with the mixture screw or jet.
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. )
Tue Jun 08, 2021 11:47 am

Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2516

 
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2516

Tue Jun 08, 2021 11:47 am linkquote
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.
Wed Jun 09, 2021 3:53 am

Hooked
PX150E
Joined: 28 Oct 2018
Posts: 148
Location: Florida, USA
 
Hooked
PX150E
Joined: 28 Oct 2018
Posts: 148
Location: Florida, USA
Wed Jun 09, 2021 3:53 am linkquote
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.
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