After recently testing a very well prepared customer bike, that was built along the exact lines of recommendations provided by us, it seems that suggested alterations to the exhaust and carburetion, in combination with fitting a substantially longer swinging arm, have worked very well indeed!
The OE exhaust system on the Bultaco is particularly poor, and after any amount of use carbon/oil sludge build up tends to reduce performance even more, and these performance losses are compounded by riders who insist on using excessive amounts of 2T oil in these machines.
It is quite possible to modify the stock Bultaco exhaust system so it works a lot better, but as the design appears to linked more to the provision of a cross pipe type spark arrestor than to engine performance, any modifications here can only be a compromise at best.
The modern type exhaust fitted on our customers bike provided a very smooth linear power delivery, as well as allowing the machine to rev much more freely at the top end, and also offered noticeably more power across the whole rev range.
Replacing the rather poor OE carburetion on a Bultaco with a modern flat slide design, is something that offers a very worthwhile improvement on any bike, but the stock air boxes and exhaust do reduce the effects of what can be gained here.
The longer swinging arm improves the grip, feel and handling of the Bultaco very noticeably. However to maintain a realistic wheelbase, the swinging arm pivot point needs to be moved forward, and this can be achieved quite neatly, and without recourse to such 1970s style mods as hacking away at the crankcases!
Gladly there is no insistence on ridiculous cassette lookalike forks for twin-shock machines at the moment, so on the Classictrial Bultaco the less than perfect stock forks and yokes will be replaced with modern parts, which are a far less costly option than altering the OE parts to work tolerably well.
Most of the changes made to this bike are easily carried out by anyone who is relatively competent at simple engineering jobs, and we will be providing detailed information on how to make these alterations, as soon as the bike we are building currently is completely finished and has been properly tested.