Two-stroke tuning is/was a black art, more akin to writing a symphony than engineering

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Reading about model airplane 2 strokes gave me that impression

The best ones were stock engines re-engineered by some extremely skilful people who were the eqivalent of good watchmakers/jewellers

Memories.

My first attempt at motorbike tuning was on a Bantam in the 1960's and the test track a country lane that now is a housing estate.

I would have a test ride and if anyone was seen hide behind the bushes untill they had gone then another test session as it was not the quietest of machines.

Tools used was a drill with stones and rotary burrs.

Later I progressed to tuning a BSA twin then supercharged Triumph twins.

A good time for the backyard mechanic.

Paul

Edited By Windy on 25/01/2013 17:54:53

Edited By Windy on 25/01/2013 17:55:32

Just reread your post - i assumed you were opening the transfer ports, not the barrel ports. Unless you have a proven pattern to work to STOP now! If you open tem in the horizontal plane you may gain a little power but risk ring flutter or worse. If you open them in the vertical plane you alter the transfer timing and this usuall gives more top end power but bottom end will suffer badly. I learned by trial and error and later by talking with Stan Stevens. Easy fix is up the compression. Easier to start and more power, and more fuel efficient - just dont go mad with it!

Jimmy there is much to consider in tuning a two stroke and particularly a BSA Bantam. I don't know if you have a copy but "Tuning for Speed" by Phil Irving is highly recommended and still highly relevant. If you haven't got a copy I suggest that you get one. Study also the effects of altering transfer ports as well as inlet and exhaust ports. Remember that packking the crankcases and increasing the compression ratio by skimming the head or getting your hands on a Todd head, and an aluminium barrel are very effective. An aluminium barrel is also much easier to work on. Have you tried the Bantam Racing Club for advice? HTH.

Tuning for speed was a bible for the fast lads even his cam and follower details are on my steamer a good read even if a bit dated.

Mines a bit dogeared now could with a new copy?

Paul

Edited By Windy on 26/01/2013 00:15:08

Many thank to all the ‘readers’ for the guidance given. I have a copy of PI’s book somewhere. The advice on the Bantam Racing Club’s site is far beyond anything I would wish to do. The George Todd article recommends simply widening and raising the top of the inlet and exhaust ports by about 2mm for ‘fast’ road work or 4mm for racing which would be adequate for my simple needs.

Further tuning would require a ‘better’ con rod/big end assembly, better quality bearings, improved piston, larger carb then an expansion box exhaust system. And so it just goes on.

Rex Caunt does an alloy barrel unmachined casting for £235 but I could not justify the expense. And Todd or B175 central plug heads are upwards of £50.

Many thanks again

Tungsten carbide burrs with a 1/4in dia. shaft are readily available and not too dear. They are infinitely better than carborundum. I have done various similar jobs and TC. is definitely preferable on cast iron.. It would not be too difficult to fix up a tubular extension to create more reach. I find that Loctite is extremely useful to fix steel to steel, instead of brazing..

I have just checked Ebay and a set of 5 suitable burrs is available for about £18.00 which is a gift.. There are also long shank ball ended cutters available. TomOl