1974 750 GT Electronic Tach not working

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gt94stang
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1974 750 GT Electronic Tach not working

Post by gt94stang » Sun Dec 30, 2018 4:20 am

Hey Guys,

In getting my GT back in running condition, I have noticed that the electronic tach does not register at all. Where does it receive it's signal from? BTW, the bike has some kind of electronic ignition in it, although I have not been able to discern which kind yet.

Also noticed that the Speedo is horrible inaccurate. Reads way to slow. Is there someone who rebuilds these Vegalia instruments that you would recommend?

Thanks,
Rob

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Craig in France
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Re: 1974 750 GT Electronic Tach not working

Post by Craig in France » Mon Jan 07, 2019 8:38 am

gt94stang wrote:
Sun Dec 30, 2018 4:20 am
I have noticed that the electronic tach does not register at all. Where does it receive it's signal from? <snip> Is there someone who rebuilds these Veglia instruments that you would recommend?
Hi Rob

I noticed you weren't getting any replies to this - or over at the Other Place - so I emailed my friend Tom Rolland, he who knows lots about these bikes. And here's what he has to say:

"The 750 GT had the Veglia electronic tach by early '73, probably around engine 751000 and they had them until around 754000. So that's 3,000 of the 7,000 Roundcases that were made.

They were known for not working. One small wire inside would break. Not sure if it was vibration or current that caused the failures.

They are driven by an electronic pulse from the coils by a wire from one of the coils to the tac.

I have one on my '73 750 GT. And it doesn't work. I had it rebuilt at North Hollywood Speedo and Instrument Repair. And it still doesn't work. I figured it might be something wrong with the wiring, but haven't checked further.

It's written about in the 750 Bible. See pages 74-75 and 79 and pages 56-57."

He adds:
"Get the engine number. The bike is probably actually a '73 and regoed as a '74. That happened a lot. The very early GTs had Smiths, first 1,000 or so; and then after 754000 or so, Ducati went back to Smiths again."

HTH - well, a bit anyways :?

Craig

gt94stang
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Re: 1974 750 GT Electronic Tach not working

Post by gt94stang » Tue Jan 08, 2019 3:00 am

Hey Craig,

That does help. Thanks for the reply. Much appreciated.

Rob

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Craig in France
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Re: 1974 750 GT Electronic Tach not working

Post by Craig in France » Tue Jan 08, 2019 9:33 am

Hi Rob,

No worries - the thanks should really go to Tom, you know. I'm just the messenger... ;).

Btw: guided by Tom, I've now found this in Ian's Bible (pg 70). He's describing the 1973 second stage models, frame nos 752100-753500 approx:

" Problems with the Veglia tachometer prompted Ducati to supply replacement Veglia mechanical tachometers with a new angle drive to some importers (notably Frasers in Australia)".

And later on (pg 72), and in reference this time to the third stage models of 1973, frame nos. 753500 -754300, Ian writes:
"By the end of 1973, all the tachometers fitted to new machines were mechanical, with the new drive from the front cylinder."

All a bit discouraging, and I dunno where it leaves you. Try to find someone to get the blessed thing working? Or just accept it as it is, as Tom has decided to do?

Ciao

Craig

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BevHevSteve
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Re: 1974 750 GT Electronic Tach not working

Post by BevHevSteve » Wed Jan 16, 2019 11:41 am

regarding speed-o drive being inaccurate,

18" or 19" front wheel?

Probably have the wrong ratio speed-o drive.....

23/11 for 19" wheel
20/10 for 18" wheel
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Craig in France
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Re: 1974 750 GT Electronic Tach not working

Post by Craig in France » Thu Jan 17, 2019 4:55 am

BevHevSteve wrote:
Wed Jan 16, 2019 11:41 am
Probably have the wrong ratio speed-o drive.....
(The same thought had crossed my mind ... 8) )

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