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750 GT charge rate?

Posted: Thu Jul 12, 2007 7:33 pm
by baddean
Hello to the gurus,
Maybe you can help.
1973 750 GT stopped on me last night. No spark. Discovered the battery was low, (I'm assuming it has a battery ignition as opposed to an alternator ignition). Have checked the obvious things. It still has the points.
With a digital volt meter across the battery I found the voltage to be 11.6 volts. ( It was below 10.5 when it would not run). It would run at 11.6 but roughly. Anyway, with the volt meter across the battery terminals and the engine running at 3500-4000rpm I get about 12.67 volts at the battery.
Now I am assuming that it is charging at that rate and lacking a proper manual I don't know if this is enough of a charge to keep the battery up.
I'm used to seeing 13.6-14 volts on more modern systems.
What charge rate should I expect to see?
Thanks to all,
Oh yeah, Steve, if you are reading this, that pic of your daughter at 3 weeks is adorable!

Posted: Sun Aug 17, 2008 3:00 am
by Crashfangio
Hi Dean,

I had a similar problem with my 73 750GT, I would only get a few hours out of a fully charged battery, even with the headlight off.

the short answer is that the standard stator/rotor combo isn't all that flash. I have heard of a Ducati ST2 conversion being done (google search same for info). In the end I purchased an up-rated stator from Road and Race here in Australia. It wasn't too pricey (under AUD$200 from memory) and I haven't had any problems since.

If you are interested, I can throw the meter across the battery and give you the stats. Road and Race (no, I'm not associated with this business) mail order to the US.

Cheers, David


Posted: Sun Aug 17, 2008 4:43 pm
by Rick F
Hi Guys,

just having the same problem with my GT.

It stopped on me last thursday, right outside a Harley owners house. Had to cop all the ususal stuff (buy a real bike etc)

Low Battery. I normally keep it on charge but hadn't for a couple of weeks

I have been expecting the problem as I did nothing to the system, except a new battery, when I was putting it back together after 20 years.

reason for the post, is I have been looking at the Road & Race website & saving my biccies for the upgrade. Phil has recently increased the price of the kit to somewhere over $400 AUD

& then he has good copies of the dash....& the CEV indicators I want......he has a great copy of the original chrome faced tyres very soon.......& I have just found a guy to replicate the original paint......

& the missus wants to send the kids to private school!
:? :?

Posted: Sun Aug 17, 2008 4:44 pm
by wdietz186
Charge rate and 750 GT were never terms that had any association together. Even when new the charging output was limp. A good battery,clean connections, and a good fusebox are essential. Running with the lights on below 4000 rpm is going to pull the battery down. Kinda even worse than Lucas electrics. I've lived with mine for 30yrs. and just don't ride at night or do much low speed riding anymore. The biggest battery you can fit and a battery tender is the simplest solution. From what I've read the ST2 setup is the way to go and not too hard to fit.

Posted: Wed Aug 20, 2008 8:06 pm
by baddean
Hi Rick,
It's an easy fix.
I have been running the Road and Race rotor in my bike for a while now with no issues at all.
I am using the stock stator and regulator with the new rotor.
You could spring for the whole kit but installing just the rotor works fine as long as the other components are in good order.
Here is a link for some info on the conversion.
And a link to the Road and Race conversion site. ... rsions.htm
The new rotor was a direct replacement. No modifications required.
Old one off, new one on.
Charges at about 14.2 volts at 3500 rpm and 13.8 at idle.
No problem with the lights either.
The modern rare earth magnets are the secret. My stock rotor wouldn't pick up a screwdriver. I had to keep the new rotor away from the tools. It wanted to grab them all.
Hope this helps, Dean
Stock rotor
ST2 rotor installed


Posted: Thu Aug 21, 2008 8:45 pm
by Rick F
Thanks Dean,

I am saving for a few things at the moment.
Also about to start a new job after a few months of twiddling my thumbs.

Thanks for the info about the ease of the change.

I have been meaning to get my bike down to Arthur at Byron Bay for a couple of things, so will either get him to do it, or at least test the system to find out what is needed.

I know I should just throw in a new battery anyway...they are cheap.. but it is strange, sometimes I go for a good ride & put it back on charge within a day or so of getting home, and it is fully charged. Other times, it takes an hour or two to come up.

anyway, the upgrade is the way to go, as I say, I did nothing to the motor after 20 years, so I am ahead anyway