Jumpy Tacho

JonnyCJ
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Jumpy Tacho

Post by JonnyCJ »

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
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Re: Jumpy Tacho

Post by OP »

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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Aspro
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Re: Jumpy Tacho

Post by Aspro »

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.
JonnyCJ
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Re: Jumpy Tacho

Post by JonnyCJ »

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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paul_f
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Re: Jumpy Tacho

Post by paul_f »

More likely to need a diode as mentioned by Aspro.
http://thelatebay.com/index.php?threads ... lly.63642/
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JonnyCJ
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Re: Jumpy Tacho

Post by JonnyCJ »

Thanks all - 10 diodes ordered for 99p delivered !
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Re: Jumpy Tacho

Post by Aspro »

Hope it works mate. Let us know
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Re: Jumpy Tacho

Post by flatbeat »

JonnyCJ wrote:Thanks all - 10 diodes ordered for 99p delivered !
Which ones did you get......got the same problem.
Cheers
Packed a few belongings and headed out to Pirates Cove. In my buddy’s old grey Kombi we rolled until the gas got low.....

1965 11 Window aka 'Rustina'.
1961 Beetle.
JonnyCJ
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Re: Jumpy Tacho

Post by JonnyCJ »

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 !
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Re: Jumpy Tacho

Post by flatbeat »

Cheers. Fingers crossed it solves the problem :D
Packed a few belongings and headed out to Pirates Cove. In my buddy’s old grey Kombi we rolled until the gas got low.....

1965 11 Window aka 'Rustina'.
1961 Beetle.
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Re: Jumpy Tacho

Post by OP »

Fitted numerous tachos and never needed a diode :?
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Hongkongphooey
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Re: Jumpy Tacho

Post by Hongkongphooey »

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

Post by flatbeat »

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...
Cool. Mines an Autometer too so I'll check to see if it's got a common earth.....I think it may have...
Cheers
Packed a few belongings and headed out to Pirates Cove. In my buddy’s old grey Kombi we rolled until the gas got low.....

1965 11 Window aka 'Rustina'.
1961 Beetle.
JonnyCJ
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Re: Jumpy Tacho

Post by JonnyCJ »

Thanks HKP - useful knowledge. Flatbeat- do report back !
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Re: Jumpy Tacho

Post by flatbeat »

JonnyCJ wrote:Thanks HKP - useful knowledge. Flatbeat- do report back !
:wink:
Packed a few belongings and headed out to Pirates Cove. In my buddy’s old grey Kombi we rolled until the gas got low.....

1965 11 Window aka 'Rustina'.
1961 Beetle.
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