Might be of help to someone ....

[Oilyspanner]

I had a Veypor  display (a Canadian gauge) and it couldn't use the original tacho's signal wire, so I linked it to one of the coil signal wires - here's a picture a year or two ago - all worked well, although it needed stick coils to get a clean rpm signal, the old HT leads interfered with the signal.

I recently played with the dyno function it had, if you enter the overall weight it had enough other data to work out how much power would be required to accelerate the bike at a known rate (it gives an idea, it's different though as wind resistance comes into it for instance). I'd done a few runs over the last couple of years, so I thought I'd upload the graphs onto my laptop …. unfortunately the auxiliary power supply fried a circuit ! I couldn't fix the burnt bit of circuit board track, so I bought a Koso DB 03r - basically the right money and told me the info I needed. This unit could use the original tacho signal lead, so I got it all working and took the bike out - the bike has gained some more low rev drive - seems with my previous tapping into the coil signal wire had affected the pair of stick coils, they obviously like a good, clean supply. I had to fiddle around a lot with carb settings to get a decent, smooth low end drive I remember - so if anyone has a problem with their stick coil conversion and has a similar rpm link, it might pay to check this. 

My bike has a big bore with fairly high compression, so asks a little more from it's ignition - it's now very noticeably harder pulling sub 4k - feels like a B12 down low now (not that I've ridden many you understand !) and combines very nicely with a very strong 4k+ that has been there since sorting my carburation after b.b. etc.

Happy days …. see if I can get out again as the sun's out.