Basic carburettor settings

Tuning a carburettor on a two stroke is probably one of the most important jobs to get correct, but can also be the most difficult. Having your engine set up professionally by a competent rolling road operator is vital to the safe running of your engine.

The table below is a guide and starting point for the most popular set ups and carbs used. Please note this is a guide only as every scooter is individual and needs different jettings. Smaller SH20/22 and PHBL jettings are for running with a GP200 sized airbox, with a hi flow filter. PHBH are for open mouthed, or when using our breathing sweet filters.

The are base settings, by this we mean they shouldget your scooter up and running, and be acceptable for running in. During this period you should keep a close eye on spark plug colour you can use our guide here. To fine tune the jetting to your scooter, you should have your scooter dynod, or you can read our fine tuning your carb guide if you feel comfortable with jettign and setting up your own scooter.
(if you are reading these instructions on paper, the other instructions that we refer to are available from our web site at www.lambretta.co.uk/technical.html)

Factory settings for standard Lambrettas with no modifications

Model Carb fitted Choke Size Slide Needle Atomizer Main Jet Pilot Jet Starter Jet Float Air Screw
Standard Lambretta set ups and jetting
150 Li I MA 19 BS5 19mm 65 D18 260 B 95 40 55 6.5gms 1/2-2 turns
125 Li II MA 18 BS5 18mm 50 D20 260 oB 93 or 73 35 55 6.5gms 1/2-2 turns
150 Li II MA 19 BS5 19mm 50 D21 260 B 102 or 78 40 55 6.5gms 1/2-2 turns
125 Li II Later Type MA 18 BS7 18mm 50 D20 260 B 73 35 55 5gms 1/2-2 turns
150 Li II Later Type MA 19 BS7 19mm 50 D21 260 B 78 40 55 5gms 1/2-2 turns
175 TV II Early MB 23 BS5 23mm 70 E15 260 B 110 40 60 6.5gms 1/2-2 turns
175 TV II  MB 21 BS5 21mm 70 E15 260 B 88 40 55 or 60 6.5gms 1/2-2 turns
175 TV II Later Type MB 21 BS7 21mm 70 E15 260 B 88 40 60 5gms 1/2-2 turns
125 Li I MA 18 BS5 18mm 50 D16 260 oB 92 35 55 6.5gms 1/2-2 turns
125 Li III SH1 18 18mm 5914-1 - 5899-1 99 42 50 5gms 1/2 turn
150 Li III SH1 18 18mm 5914-2 - 5899-1 105 45 50 5gms 1/2 turn
Li 125 Special SH1 20 20mm 5914-2 - 5899-4 98 45 50 5gms 1/2 turn
Li 150 Special SHI 18 18mm 5914-1 - 5899-2 101 45 50 5gms 1/2 turn
175 TV III SH1 20 20mm 5914-1 - 5899-2 106 50 50 5gms 1/2 turn
200 TV SH1 20 20mm 5914-1 - 5899-2 108 48 50 5gms 1/2 turn
SX 150 SH1 20 20mm 5914-2 - 5899-5 102 45 50 5gms 1/2 turn
SX 200 SH1 20 20mm 5914-1 - 5899-2 103 48 50 5gms 1/2 turn
GP 125 SH1 20 20mm 5914-2 - 5899-4 98 45 50 5gms 1/2 turn
GP 150 SH1 22 22mm 7895-2 - 5899-4 118 45 50 5gms 1 - 2 turns
GP 200 SH1 22 22mm 7895-1 - 5899-2 118 45 50 5gms 1 - 2 turns
Lui 50 SH1 mm - 50 5gms 1 turn
75 S Vega
75 SL Cometa
SH1 20 20mm 5914 - 1 - 5899 - 6 68 45 50 5gms 1 turn
J50 SHB 18/16 16mm 6493 - 2 - - 60 40 50 3.5gms 3/4 turn
Cento 100 SHB 18/16 16mm 6492 - 1 - - 70 40 50 3.5gms 3/4 turn
J125 SHB 18/16 16mm 6492 - 1 - - 72 40 50 3.5gms 3/4 turn
J125 Starstream SHB 18/16 16mm 6492 - 1 - - 72 40 50 3.5gms 3/4 turn
Model Carb fitted Choke Size Slide Needle Atomizer Main Jet Pilot Jet Starter Jet Float Air Screw


Modified / Tuned / Kitted Lambrettas, base jetting details
Budget 175/185 kits
  Ancilotti
SH1 22 22mm 7895-1 - 5899-2 118 45 50 5gms 1 - 2 turns
Budget 175/185 kits
  Ancilotti
SH1 22 22mm 7895-1 - 5899-2 125 48 50 5gms 1 - 2 turns
Budget 175/185 kits
  Ancilotti
PHBH 26/28/30mm 30 X7 AV264 100 45 50 5gms 1 - 2 turns
Budget 175/185 kits
  Expansion
PHBH 26/28/30mm 40 X7 AV266 120 48 50 5gms 1 - 2 turns
Mugello 186/200
  With Ancilotti
SH1 20 20mm 5914-1 - 5899-2 120 48 50 5gms 1/2 turn
Mugello 186/200
  With Expansion
SH1 20 20mm 5914-1 - 5899-2
Drilled
120 50 50 5gms 1/2 turn
Mugello 186/200
  Ancilotti
SH1 22 22mm 7895-1 - 5899-2
Drilled
122 48 50 5gms 1 - 2 turns
Mugello 186/200
  Expansion
SH1 22 22mm 7895-1 - 5899-2
Drilled
128 55 50 5gms 1 - 2 turns
Mugello 186/200
  Ancilotti
PHBL 25mm 25mm 45 D22 AQ264 110 50 50 5gms 1 - 2 turns
Mugello 186/200
  Expansion
PHBL 25mm 25mm 45 D22 AQ266 120 55 50 5gms 1 - 2 turns
Mugello 186/200
  Ancilotti
PHBH 26mm 26mm 45 X2 AV264 100 50 50 5gms 1 - 2 turns
Mugello 186/200
  Expansion
PHBH 26mm 26mm 45 X2 AV268 110 50 50 5gms 1 - 2 turns
Mugello Ultimate
186/200

  Ancilotti
PHBH 26mm 26mm 53 X7 AV266 102 50 50 5gms 1 - 2 turns
Mugello Ultimate
186/200

  Expansion
PHBH 26mm 26mm 53 X7 AV268 115 50 50 5gms 1 - 2 turns
Mugello 186/200
  Ancilotti
PHBH 30mm 30mm 45 X2 AV266 105 53 50 5gms 1 - 2 turns
Mugello 186/200
  Expansion
PHBH 30mm 30mm 45 X2 AV268 120 55 50 5gms 1 - 2 turns
Mugello Ultimate
186/200

  Ancilotti
PHBH 30mm 26mm 53 X7 AV266 103 50 50 5gms 1 - 2 turns
Mugello Ultimate
186/200

  Expansion
PHBH 30mm 26mm 53 X7 AV268 118 50 50 5gms 1 - 2 turns
Imola 186
  Ancilotti
PHBH 30mm 30mm 50 X2 AV266 110 55 50 5gms 1 - 2 turns
Imola 186
  Expansion
PHBH 30mm 30mm 50 X2 AV268 120 55 50 5gms 1 - 2 turns
Mugello 225
  Ancilotti
PHBH 26mm 26mm 45 X2 AV268 110 50 50 5gms 1 - 2 turns
Mugello 225
  Expansion
PHBH 26mm 26mm 45 X2 AV268 120 50 50 5gms 1 - 2 turns
Mugello 225
  Ancilotti
PHBH 30mm 30mm 45 X2 AV268 115 53 50 5gms 1 - 2 turns
Mugello 225
  Expansion
PHBH 30mm 30mm 45 X2 AV268 125 55 50 5gms 1 - 2 turns
Monza 225
  Ancilotti
PHBH 30mm 30mm 45 X2 AV268 118 55 50 5gms 1 - 2 turns
Monza 225
  Expansion
PHBH 30mm 30mm 50 X2 AV268 130 55 50 5gms 1 - 2 turns

Typical problems and cures