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Misc: Ignition Electric Rev Counter and B.T.H

Mark Fisher

Well Known and Active Website User
VOC Member
I'm hoping somebody might know this, I have bought an electronic rev counter for my Norvin from Legendary motorcycles here in the US and I'm not sure which wire on the modern BTH coils I need to connect the sensor wire from the tach to, anybody know? I'm aware that there is a possibility that I may have to buy a separate sender which clips to one of the HT leads, but I'm hoping that's not the case. I'm not sure who the actual manufacturer is but they are made to look like "green globe" commando clocks and have the legendary logo on them. I asked legendary but they weren't familiar with the BTH.
thanks
mark
 

vibrac

Well Known and Active Website User
VOC Member
I always used a wrap wire pickup on a plug lead for all my BTH rev counter bikes worked for all my racers you could suck it and see if you want to try the coil leads but I would bear in mind that BTH had a reputation for getting interruptions in use from the cut out wire (I know I cut mine off ts source) so that effect might be picked up by a rev counter wire pickup Mine was never affected by the HT lead wrap around pickup.It may even be the case that later BTH mags had more radiation sheilding
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
The BT-H have this rev-counter information on their webpage:-

"Question 16: Can I use an electronic rev counter with my new BTH magneto?
Answer: Several people are successfully using the self-powered the Scitsu electronic rev counter. Nick Brown, of A.J.S. Motorcycles, has sent us this advice. (See Note 2.) Another rev counter we have successfully tried is sold by Mick Hemmings. This simply needs a diode (IN4001 or similar) in the sensing lead and a12 volt supply.
Re: Scitsu Tachometers: The single Magnetos use a yellow unit. The black model is recommended for a 360 twin with BT-H high output mag. You should connect the Tacho sensor wire to both HT leads. V twins are tricky because of the uneven firing pulse. the 1-2 space, 1-2 space, firing order can confuse the Tacho, so it is best to treat V twins like a single and try to keep the sensor wire away."

Mick Hemmings died a while back and I think his rev-counter supplier had stopped making them. These used a 12 volt supply for the electronics and the sensing wire was wrapped around the plug lead.
The Scitsu units worked well and had their own rechargeable battery. They maybe also have made one that could be powered. The sensing wire wrapped around a plug lead. Don't try to feed any rev-counter direct from the output from leads to the spade connectors on the coil/s as the output to the coils in the hundreds of Volts.
 

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