When carrying out tuning, all these motors can be converted to use later specification cylinders, crankshafts, carbs and exhausts. This is more beneficial if you want to keep and use only standard parts. The GP125 motor for instance is considerably more powerful than an LI 125 engine. A GP150 is more powerful than an SX150, which is more powerful than an LI150 engine.

When a very high level of performance is required it is also necessary to uprate components to the later specification. All 125 cylinders can be bored to 150cc, all 150cc's to 175. The original head can be opened to suit and also raise the compression ratio. A 175 cylinder can be bored to 200cc when a conrod of 107mm is used so the standard 200 GP piston is used but the cylinder is very thin. It is occasionally possible to obtain 65mm pistons that fit with the TV175 conrod (116mm long) which at least allows a 175 cylinder to continue to be used when it runs out of oversizes.

In general, LI's use 18mm carbs, SX's 20mm, and GP's 22mm (GP125's use 20mm). So the use of a GP 22mm carb and manifold will allow greater performance with a standard looking motor. For those who want more, a Dell'Orto 25mm carb can be used on modified manifold with the airbox, or 28/30mm type carbs without the airbox, when maximum performance is required with 150-175 and 190 cylinders with tuning.

It is also possible to use the Series 3 exhausts on Series 2 motors or Big Bore Indian or Clubman type
exhausts. These are better suited when porting work is carried out.
To maximise performance, expansion chambers are available to further suit stage 3 or higher levels.

Porting can be divided into several areas:

Stage 1/2/3 - generally for softer road tune using standard or near-standard components.

Stage 3/4 - for use with larger carbs and Big Bore exhaust systems.

Stage 5/6 - for use with Japanese pistons when performance with maximum reliability is required. This stage of tune needs GP-type crankshafts and flywheels for maximum mileage and reliability. On an SX or LI crankshaft, this type of tune is just a waste of money. If the performance available is used, the flywheel tapers break and the conrod big-end pins shear.