LCGB Forums

Hi -- after multiple attempts to jet my 30mm dellorto properly I'm nearly there. I have a spot on 1/2 throttle that splutters a bit, twitch the right wrist and it goes away but it's right on where i like to drive. Set up is
Stage 4 200cc
30mm Delly - Open Mouthed
42mm AF Clubman
2 1/4 turns out
50 pilot
70 choke
40 slide
AV264 atomiser
X7 needle with clip top
123 main jet

My question is should I try and get perfect with a needle change & is it worth the hassle and if so what would it be to lean it out a teeny tiny bit? Seriously it's taken me years to get this right including stator changes the lot. All advice appreciated -- G

Hi Steve. I admire your persistence.

Do you know the exact throttle position where the blip occurs? I mean, have you set up a marker on the throttle side so you can recreate how far the slide is open. You can then work out how far up (or down) the needle you need to improve upon the X7 taper. You can then check this against a needle chart and see if there is something suitable to fill the gap.

BGM do packs of similarly-sized needles at a good price.

If this doesn’t make sense, call me using your good arm.

you're @ the 2nd weakest needle now bud
weak atomisor
weak pilot
weak slide
plug chop bud

40 is a rich slide 50 is leaner.

I set this up for a mate, it has a breath sweet filter.

It's just been to Whitby and back (300 miles) no issues rides nice through the gears and cruises at 60 all day with a bit left.

Cast iron 200

Main 125
Choke 50
Pilot 50
Atomiser AV266
Slide 40
Needle X2
Float valve 200
With AF pipe


Li150 box 16-46

Granty wrote:Hi -- after multiple attempts to jet my 30mm dellorto properly I'm nearly there. I have a spot on 1/2 throttle that splutters a bit, twitch the right wrist and it goes away but it's right on where i like to drive. Set up is
Stage 4 200cc
30mm Delly - Open Mouthed
42mm AF Clubman
2 1/4 turns out
50 pilot
70 choke
40 slide
AV264 atomiser
X7 needle with clip top
123 main jet

My question is should I try and get perfect with a needle change & is it worth the hassle and if so what would it be to lean it out a teeny tiny bit? Seriously it's taken me years to get this right including stator changes the lot. All advice appreciated -- G

You could try an x12 needle but it seems quite lean to me already.

https://www.lambrettaspares.com/pages/d ... EEDLES.pdf

It seems to me that regardless of the particular model variant, all Dell'Orto's require roughly the same settings from the better types {VHSC's) down to the PH's so popular with many Lambretta owners,

My experience has found time after time that slides of 40 to 45 are what are required, with a definite tendency to 45, even on full race engines.

Unfortunately, even though Dell'Orto's are inherently tuneable by virtue of the massive range of component parts available, slides are not cheap. I would suggest borrowing a 45 slide if possible prior to buying outright. If a 45 cleans up the flat spot, a 40 can be modified with care to become a 45. It's just a matter of removing a small amount of material from one edge, a practice fairly common years ago with the likes of Taffspeed etc, I don't know the amount off hand, but it can be readily calculated by comparing a 40 with a 50 & halving the difference for a 45. On one occasion, even a DIY 42.5 was made to suit a VHSC,

Before anybody else questions the atomizer size, 264 should be fine. A bigger atomizer will result in loss of fine fuel control. If in doubt, run the engine on the stand with no main jet fitted. If it does run anything like when a main jet is fitted, there is a problem - if it runs like a crock of sh1te, then all is well & pop the main jet back in,

The only other thing worthy of mention is the float valve. Theoretically, 200 is fine but IMHO a bit near the edge in terms of safety margin. Whilst I do not agree with 'the bigger the batter' as so many seem to advocate, if buying some other parts, you might want to add a 250/300 to your shopping list,

I hope my suggestions help in some way

hullygully wrote:you're @ the 2nd weakest needle now bud
weak atomisor
weak pilot
weak slide
plug chop bud

Yip, when you put it like that ..... I've tried a AV266 and the thing just bogged down terribly to the point of useless. I'll just be leaving it I think -- G

Have you tried an x13 needle with the AV264?

Warkton Tornado No.1 wrote:Before anybody else questions the atomizer size, 264 should be fine. A bigger atomizer will result in loss of fine fuel control. If in doubt, run the engine on the stand with no main jet fitted. If it does run anything like when a main jet is fitted, there is a problem - if it runs like a crock of sh1te, then all is well & pop the main jet back in,

Do you mean when the throttle is wide open and therefore sucking fuel through, only restricted by the atomiser tube? So I'm thinking if it runs something like the main is still in place, then the atomiser is too small?

Have I got the gist of it?

Storkfoot wrote:Have you tried an x13 needle with the AV264?

No, that was going to be the next experiment, if anyone has run that combo give me a shout?

Yes, I have used that combination on a standard TS1. Someone more knowledgeable than me told me that, on a Lambretta, the X13 tends to work well with the AV264.

dickie wrote:

Warkton Tornado No.1 wrote:Before anybody else questions the atomizer size, 264 should be fine. A bigger atomizer will result in loss of fine fuel control. If in doubt, run the engine on the stand with no main jet fitted. If it does run anything like when a main jet is fitted, there is a problem - if it runs like a crock of sh1te, then all is well & pop the main jet back in,

Do you mean when the throttle is wide open and therefore sucking fuel through, only restricted by the atomiser tube? So I'm thinking if it runs something like the main is still in place, then the atomiser is too small?

Have I got the gist of it?

Yes.

Obviously the only restriction @ WOT should be the main jet. The atomizer should be large enough so that it never becomes a restriction. Whilst many then may consider an even bigger atomizer the better option, the trade-off is in the control that the needle within the atomizer can then offer. Taken to extremes, were a 270 atomizer be fitted where a 264 was adequate (with some safety margin) the gap between atomizer & needle would be considerably greater, the consequences being that the fuel delivery would be far greater than necessary with the carburetor only leaning off again toward optimum as WOT was approached.

The control of fuel delivery is important if an engine is to be tractable @ all points through it's operational rev range & precisely why a keen rider/tuner will keep an eye on the needle & atomizer for any indication of wear.

Storkfoot wrote:Yes, I have used that combination on a standard TS1. Someone more knowledgeable than me told me that, on a Lambretta, the X13 tends to work well with the AV264.

Thanks for this, I'll try and report back