adam_winstone

Another step closer... I've come across a service manual that states the 250cc scrambler came in 2 options; the motocross version that had a 64mm long inlet side piston skirt and the TT version that had a 59mm skirt. I'll have a look through the porting measurements given again and work out the inlet timing for both piston options, although it is likely that the respective barrels also had different exhaust port timing to help produce power at the desireable rev range. Cool! Adam

Okay, next (hopefully last!) question.... Do all of the 250s run the a similar length piston? The shorter the piston skirt on the inlet side, the longer the port open duration. I've managed to plug the measurements that you kindly gave into a spreadsheet but need to know what the measurement is from the edge of the piston crown (above the rings) to the bottom of the skirt length is? Even if the pistons did vary somewhat, I can plug a single piston measurement into the spreadsheet and it should allow me to compare port timings anyway. Thanks in advance, Adam PS - Regarding your M157 item... whilst most Bultaco model lists have this down as a Sherpa T 125, I came across one list that had it as a 'Lobito S 238 Prototype'... perhaps an error, perhaps a treasure!!!

Excellent stuff, thanks.

feetupfun, Thanks for the response. Yep, any info that you could offer regarding inlet, transfer or exhaust port measurements would be great If you could give me the measurements from top and bottom of port to the top lip of the bore (head gasket face) then I'll see if I can find a suitable port timing calculator on-line, of which there are many. A width of port measurement would also allow me to calculate the port's area but will not change the duration figure. Thanks for the offer.... YES PLEASE Adam

No takers then If anyone knows the standard port timings of any of the models then I would love to hear from them. I'm not expecting any one response to cover all models. Any help appreciated. Thanks, Adam

Hi All, After spending lots of time searching the web for info on the older Bultaco 2-strokes, I'm at a complete loss and need some help from anyone who knows about these bikes/motors. What I'm after is some basic cylinder porting information (e.g. inlet port duration, transfer duration, exhaust port duration) so that I can see how the 250 motors developed, specific to their applications (flat-track racing or trials). I managed to find Bell's tuning info regarding the Matador's 150 inlet, 126 transfer & 170 exhaust timing but that's all I've managed to find. Please note that I'm not looking to steal anyone's tuning methods/port timings, I just want to be able to see how port durations changed in comparison to carb size, compression ratio, gearing, etc. The BHP @ RPM figures for the various models suggest that cylinder porting changed between models, as do other factors (e.g. 27mm to 32mm carbs), and this is what I'm hoping to learn more about. If anyone out there happens to know the 'real' technical spec of these motors, I'd love to hear from you and talk technical Thanks in advance. Adam