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Jumpy Tacho
by JonnyCJ » Wed Sep 21, 2016 11:05 am
I've installed a Sumex Race Sport tacho in my bus (paid a bit for it rather than a cheap one from ebay).
The tacho needle however jumps all over the place. Sometimes it records about the right revs, sometimes zero, sometimes no where near the right reading.
I have a Lucas coil, Accuspark electronic ignition, new plugs and leads, new dizzy cap and a SVDA dizzy.
I've read that resistance on tachos can be an issue but thought I'd plug into the wisdom of the forum first.
Cheers
Jonny
The tacho needle however jumps all over the place. Sometimes it records about the right revs, sometimes zero, sometimes no where near the right reading.
I have a Lucas coil, Accuspark electronic ignition, new plugs and leads, new dizzy cap and a SVDA dizzy.
I've read that resistance on tachos can be an issue but thought I'd plug into the wisdom of the forum first.
Cheers
Jonny
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Re: Jumpy Tacho
by OP » Sat Sep 24, 2016 1:56 pm
Have you connected it to a shared earth? If so connect it to it's own earth. I had the same problem with a Mooneyes one years ago and this solved the problem.
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Re: Jumpy Tacho
by Aspro » Sat Sep 24, 2016 3:33 pm
You need a diode in line with the coil feed. Cost a few pence from your local electronics store or you can buy them off ebay.
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Re: Jumpy Tacho
by JonnyCJ » Sat Sep 24, 2016 7:03 pm
Thanks chaps - think I'm on a common earth so will get it changed tomorrow and see if that makes a difference.
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Re: Jumpy Tacho
by paul_f » Sat Sep 24, 2016 7:55 pm
More likely to need a diode as mentioned by Aspro.
http://thelatebay.com/index.php?threads ... lly.63642/
http://thelatebay.com/index.php?threads ... lly.63642/
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Re: Jumpy Tacho
by JonnyCJ » Sat Sep 24, 2016 8:30 pm
Thanks all - 10 diodes ordered for 99p delivered !
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Re: Jumpy Tacho
by Aspro » Sat Sep 24, 2016 11:07 pm
Hope it works mate. Let us know
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Re: Jumpy Tacho
by flatbeat » Sun Sep 25, 2016 2:20 pm
Which ones did you get......got the same problem.JonnyCJ wrote:Thanks all - 10 diodes ordered for 99p delivered !
Cheers
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Re: Jumpy Tacho
by JonnyCJ » Sun Sep 25, 2016 4:37 pm
Went for the 1N4005
Will report back on how it goes in a week or two. Just dropped the bus off to have some trimming snagging finished off, so will be without it for a few days.
If it works I'll pop the others in the post to you. Can't see me needing any more !
Will report back on how it goes in a week or two. Just dropped the bus off to have some trimming snagging finished off, so will be without it for a few days.
If it works I'll pop the others in the post to you. Can't see me needing any more !
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Re: Jumpy Tacho
by flatbeat » Sun Sep 25, 2016 5:50 pm
Cheers. Fingers crossed it solves the problem
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Re: Jumpy Tacho
by OP » Mon Sep 26, 2016 2:51 pm
Fitted numerous tachos and never needed a diode
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Re: Jumpy Tacho
by Hongkongphooey » Thu Sep 29, 2016 12:26 pm
Change to its own earth as close as possible to the Tacho. I have an Autometer Tacho was fine on its own earth but I 'Tidied' the wiring up and changed it to a common earth and the needle would twitch as you described, changed back to its own earth and it is fine now...
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Re: Jumpy Tacho
by flatbeat » Thu Sep 29, 2016 4:06 pm
Cool. Mines an Autometer too so I'll check to see if it's got a common earth.....I think it may have...Hongkongphooey wrote:Change to its own earth as close as possible to the Tacho. I have an Autometer Tacho was fine on its own earth but I 'Tidied' the wiring up and changed it to a common earth and the needle would twitch as you described, changed back to its own earth and it is fine now...
Cheers
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Re: Jumpy Tacho
by JonnyCJ » Thu Sep 29, 2016 5:07 pm
Thanks HKP - useful knowledge. Flatbeat- do report back !
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Re: Jumpy Tacho
by flatbeat » Thu Sep 29, 2016 6:00 pm
JonnyCJ wrote:Thanks HKP - useful knowledge. Flatbeat- do report back !
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