Stage 1 Tuning

As some of you will know, back in the late 1980's a lad called Steve from Aldershot set up and ran the Vega Owners Club and as part of that he produced a club newsletter - I have 4 editions which i think is all that was produced.

Anyway, in Issue 1 he looked at Stage 1 tuning for the Vega and Cometa and I'll reproduce it here for anyone who is interested.
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Approximately 25% increase in power can easily be achieved by alteration to the following:

Cylinder ports, air filter box, main jet and cylinder head. It is most important that the conversion be carried out completely and thoroughly as, with two stroke timing one port cannot usually be modified in isolation to the rest of the engine.

The compression ration should be raised from 9:3-1 to 9:9-1 by skimming approximately 15 thou of the head. This work should be entrusted to your local engineering firm. An improved cylinder head was available (20851016) with the spark plug fitted to the nearside of the machine instead of the offside and this is a great help to plug life when the engine is tuned. A new cylinder cowl (20855340) will also be required as the spark plug fitting hole is of course now moved.

The exhaust port should be raised by 1mm and the inlet lowered by 2mm. This will give the resultant dimensions from the top of the cylinder of 29mm for the top of the exhaust port and 64mm for the bottom of the inlet port.

Great care must be taken when modifying the ports and use of the proper equipment is imperative. A flexible drive with various cutting tools is ideal and these should only be used on the side of the port to be altered. Once the port measurement is near to that specified, all the remaining metal should be removed by polishing with emery cloth. A quarter inch diameter rod slotted along its length for about 1 inch is useful for rotating the emery in an electric drill or flexi drive.

The most complicated and important part of this conversion is the air filter box A new centre baffle must be made to the following dimensions. Brass or aluminium are suitable materials.

A 6mm bolt 25 or 30mm long should be fitted in the baffle from the inside to act as a stud. Loctite should be used to secure it and to prevent loosening.

The air filter box should be carefully cut open along the seams and the original plastic baffle removed, This is extremely difficult and should be carried out with great care to avoid cracking the box. The new baffle must be glued along all of the seams around the new baffle.

Finally the main jet should be upped from 68 to 78 (00412297).

No modification to the exhaust is necessary at all not even removing the plate at the back. It is in fact detrimental to the running of the machine.

I agree about the exhaust. With hindsight I wish I had never taken the baffle out.

A 25% power increase without raising the cc's! No larger piston, no re bore, that's quite revolutionary for the time and probably inexpensive compared to modern practice.

That’s really helpful, I’m just building a standard engine & so more power for little money sounds good!