Which Carb To Use

Tuning theories differ greatly on carbs, in the past the theory big is best with carburation is not always the case. Smaller carbs tend to promote torque and cleaner running, larger carbs tend to promote more top speed, at the expense of bottom end power. You can as with everything in life go to small or to large, either starving the engine, or flooding it, again you need a happy medium.
Roughly speaking

125 to 150cc keep the original carb size
175 (tuned) 22 to 28
200 + (tuned) 25 to 30
So the most common questions we get asked are carburation and jetting help
We are not covering jetting / setting up on this page, as we have written a complete guide on how to jet your carburettor on our Help & Downloads page
We use Dellorto Carburettors, and nothing else. They are relatively cheap, reliable, and have a vast mountain of jets available.

In reality the size of carburettor needs to be chosen by the cc of your scooter, level of tune / cylinder kit, the air intake system and the exhaust, not just one factor.

DellOrto SH18
Dellorto SH1/18 carbs are no longer manufactured, so if using one make sure it is good condition, preferably fitting new jets, slides etc if worn.
Use for standard 125 or 150cc machines only.

DellOrto SH20
Originally fitted to quite a few different Lambretta models, the 20mm carb is ideal for more standard types of cylinder kits
Use on standard 150 to 175 kits running through the air box.

DellOrto SH22
Originally fitted to the most powerful factory Lambrettas, the GP150 and GP200, the SH22 still is a great work horse for some.
Jetting is pretty simple as there are not a whole host of different jets to choose from. Apart from the pilot and main, you have two choices of slide or atomiser. Once you get over 130 or so in main jet size, you would need to modify the atomiser for it to be able to feed the main jet enough fuel.
If your adamant you want original looks, and to run through your air box, it will sacrifice some top end speed, but run cleaner throughout the rev range.
150 - 175 - Casa 185 - Scootopia 185 - 200.

Dellorto PHBL
Smallest of the more modern carbs from Dellorto, they can range in sizes from 20 to 26mm. Most people use 24 / 25 / 26, with the middle one being probably the most widely used.
The PHBL are highly configurable with masses of jets, needles and atomisers available. In truth most Lambrettas will stick to a handle ful of sizes, making it easier for the average user to sort out.
150 - 175 - Casa 185 - Scootopia 185 - Mugello 186 - BGM 195 - GT186 - Mugello 198 - Mugello 200 - GT200 - Mugello 225

Dellorto PHBH
Probably THE most common carb used within the scootering world, the PHBH has been around for ever. You can get them in solid mount, rubber mount, as well as many other guides and choices.
The cheapest and easiest way to add power by way of carburation, the PHBH is available in 26 / 28 /30mm and works well with piston port engines. as well as reed. Box pipe, or expansion, the PHBH can cope with them all
150 - 175 - Casa 185 - Scootopia 185 - Mugello 186 - BGM 195 - GT186 - Imola 186 - SuperImola 186 - Mugello 198 - Mugello 200 - GT200 - Monza 200 - Mugello 225 - Monza 225 - SuperMonza 225
26mm PHBH gives better low down cleaner running, at the expense of some top end speed. Ideal for use with box pipes
28mm PHBH is piggy in the middle, works as an average on any motor.
30mm PHBH while it can be fitted to small cc motors with box pipes etc, you will get more speed, but at the expense of some low down power grumbling and added fuel consumption. Comes into its own and works well on reed engines, 200cc+ and any thing with an expansion exhaust.

Dellorto VHSH
The VHSH differs from the PHBHL and PHBH range by having a flat slide. This allows the carburettor to the slimmer, and work more efficiently.
While you can use the more exotic VHSH on smaller motors, it excels on the way it delivers the fuel mixture to the engine, giving cleaner running, more power, and even better efficiency over the PHBH / PHBL.
In fact the only down side to the VHSH is its price.
150 - 175 - Casa 185 - Scootopia 185 - Mugello 186 - BGM 195 - GT186 - Imola 186 - SuperImola 186 - Mugello 198 - Mugello 200 - GT200 - Monza 200 - Mugello 225 - Monza 225 - SuperMonza 225 

Adding a Power Jet
The main problem with standard carbs is that they rely heavily on the atomiser and main jet, and as such the main jet is required to deliver the fuel over too large a throttle opening. This means to get your jetting correct fairly correct, at some point you will have lean spot(s). Lean spots create heat, heat creates holes or seizures. The power jet adds a 4th dimension to the setting up and tuning of a safe reliable engine, especially now with the extra ethanol being added by fuel companies which promotes further heat into your engines. The Power jet allows extra fuelling in the mid range, which let's face it is where most engines sit when cruising and vulnerable.