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The first 200 motors date back to the TV200 or GT200 in the UK. These were based on the smaller motors with larger cylinders and different cylinder stud spacings. The GT200 motor ran very high overall gearings and was claimed to do in excess of 70mph as standard.
The GT200 motor was a bit fragile and was detuned and fitted with lower gearing and sold as the SX200. This was the main Lambretta 200 model until the advent of the GP200 engine with stronger crankshaft and flywheel and larger carb. The Indian-made GP200 is based on this Italian motor with alterations to the gearbox ratio, exhaust
system and carb jetting. Later Indian engines have better cylinders, better crankshafts and electronic ignition as standard, with higher overall gearing. In general, tuning of these motors takes the form of larger carbs, better exhausts, cylinder porting and 225 rebores. We have produced separate tuning guides for the Honda 205 and TS1 conversions, but the more basic tuning is covered here.
Carburetor
The standard carb is 20mm on the GT/SX 200 and 22mm on the GP200. If the air filter box is still required the normal mod is to use a Dell’Orto Phbl 25mm on a special manifold and the GP125 air hose is used to connect to the air box. If the air box is not required then 28mm and 30mm solid or rubber mounted Dell’Ortos are popular with stage 3 or 4 tunes.
Exhaust
Indian 38 Big Bore system or 42mm Clubmans are ideal for those who want the standard look. For maximum performance an expansion chamber exhaust gives more punch and power.
The GT200 motor was a bit fragile and was detuned and fitted with lower gearing and sold as the SX200. This was the main Lambretta 200 model until the advent of the GP200 engine with stronger crankshaft and flywheel and larger carb. The Indian-
system and carb jetting. Later Indian engines have better cylinders, better crankshafts and electronic ignition as standard, with higher overall gearing. In general, tuning of these motors takes the form of larger carbs, better exhausts, cylinder porting and 225 rebores. We have produced separate tuning guides for the Honda 205 and TS1 conversions, but the more basic tuning is covered here.
Carburetor
The standard carb is 20mm on the GT/SX 200 and 22mm on the GP200. If the air filter box is still required the normal mod is to use a Dell’Orto Phbl 25mm on a special manifold and the GP125 air hose is used to connect to the air box. If the air box is not required then 28mm and 30mm solid or rubber mounted Dell’Ortos are popular with stage 3 or 4 tunes.
Exhaust
Indian 38 Big Bore system or 42mm Clubmans are ideal for those who want the standard look. For maximum performance an expansion chamber exhaust gives more punch and power.
Tuning of the Cylinder
Because of the many variations in port timings used it is not possible to give specific porting information. In general, follow the tuning instructions in the Lambretta Performance manual if a standard carb and exhaust is to be used. If an expansion chamber and large 28mm carb will be used then porting can be much more extensive. The choice of exhaust and carb and the required use will affect the degree of porting done to the cylinder.
Some pistons have been produced with 1.5mm rings but these normally have a cut inlet skirt to increase inlet timing. It is therefore important to allow for this extra timing when modifying cylinders. Normal good quality pistons with the standard 2mm rings are perfectly adequate for road tunes.
Because of the many variations in port timings used it is not possible to give specific porting information. In general, follow the tuning instructions in the Lambretta Performance manual if a standard carb and exhaust is to be used. If an expansion chamber and large 28mm carb will be used then porting can be much more extensive. The choice of exhaust and carb and the required use will affect the degree of porting done to the cylinder.
Some pistons have been produced with 1.5mm rings but these normally have a cut inlet skirt to increase inlet timing. It is therefore important to allow for this extra timing when modifying cylinders. Normal good quality pistons with the standard 2mm rings are perfectly adequate for road tunes.
