Page 1 of 1
Tacho over reading
Posted:
Sat Aug 03, 2019 3:14 pm
by MikeB
Folks,
Have fired up the engine in my 1971 Sprint for the first time and the motor is running fine. As a precaution I fitted a new 23D type distributor and then put in a Lumenition Classic system. The tacho at idle appears to be reading twice the amount of revs, this was confirmed when we plugged in a rev /dwell angle reader, which showed 1000 rpm, when the tacho said 2000.
Has anyone had this occur before? I did a quick search, but seemed to find more about under reading than over reading.
Re: Tacho over reading
Posted:
Sun Aug 04, 2019 7:28 am
by rgh0
where have you powered your lumenition from ?. If its from the coil positive you may double the pulse count and thus double the tacho reading
cheers
Rohan
Re: Tacho over reading
Posted:
Sun Aug 04, 2019 7:59 am
by MikeB
Thanks, Rohan, will check
Re: Tacho over reading
Posted:
Sun Aug 04, 2019 4:04 pm
by Bigbaldybloke
Mine also reads approx double with a Pertronix system, I?ve added a recommended interface box, but it?s still not right. Have abandoned it for a while due to fitting new kitchen for wife, but must get back on to it in the next week or so.
Re: Tacho over reading
Posted:
Sun Aug 04, 2019 8:13 pm
by Evante
Where should the tach be powered from?
Re: Tacho over reading
Posted:
Sun Aug 04, 2019 8:39 pm
by MikeB
I assume the Positive to the coil feeds the signal to the tach, afterall if you are running points it?s the only wire connected to the loom ( the Neg only goes from the coil to the distributor).
So I suppose the question is how remote from the Coil positive does the Lumenition positive have to be, do you need to fit it via a relay with a permanent positive feed turned on by the ignition switch?
Re: Tacho over reading
Posted:
Sun Aug 04, 2019 10:12 pm
by rgh0
Yes you need to take it from a supply turned on by the ignition switch that is separate from the positive that goes through the tach to the coil. The lumention generates a current pulse in its supply every time it triggers the ignition and this can be read by the tach and added to the pulse the coil generates
cheers
Rohan
Re: Tacho over reading
Posted:
Mon Aug 05, 2019 9:45 am
by MikeB
Cheers Rohan, will sort that out