8. Tuning & performance

Assembly manual

8. Tuning & performance
Richard Taylor wrote this manual.

Always be aware that most tuning will be at the expense of reliability and certainly longevity (with the exception of point 5). Having said this there are several ways you can increase the performance of this kit.
1. Matching the gasket faces. The iron barrel has larger transfer ports than the engine casing. Matching (sometimes known as “blue printing”) the casing to the larger barrel ports will make an appreciable increase in

2. Exhaust system. The intended use of the kit is as a fast touring kit, usually with the use of big bore exhaust systems. Fitting a suitable expansion chamber (Franspeed race or super tour) will increase this power. In most
cases a noticeable “power band” becomes evident.

3. Inlet. The standard inlet feeds from the left-hand side of the engine for standard looks (25mm for small block, 30mm for big block). A 30 or 34mm inlet manifold can be bought to feed more directly from the right hand side
and utilise larger carburettor bodies. Obviously this will be at the expense of the battery tray on most scooters.
All GT manifolds and reed valves are inter-changeable.

4. Porting work. This principally involves grinding & polishing ports, inlet and piston. It is a “black art” and a job best done by a respected professional. SpliffSpeed here on this website should be your first port of call.

5. Gearing. This is by far the easiest improvement to make and will give instant results with no reliability problems. With the extra power provided by the conversion, it is very beneficial (if not essential) to increase the gear ratio
to improve top speed & fuel economy. For 150 gearboxes a simple change to a 17 tooth primary drive will give improved performance at a low cost. For Li125 gearboxes a combination of 82 link chain and 18 tooth primary drive sprocket and 46 tooth crown wheel. Use a Gran Turismo chain tensioner for increased flexibility in primary ratio.

Section index

1. Pre-fitting kit preparation
2. Installation preparation
3. GT186 Stock Touring Installation steps
4. Air box installation amendments
5. Carburettors, jetting & sparkplugs
6. Running in
7. Care and Maintenance
8. Tuning & performance
9. Disclaimer
10. Trouble shooting
11. Cylinder head specifications
12. Suggested specifications