750T ignition question

Hi all, I have been using the 750T quite a bit recently. A trip up to London to get a new passport as I had forgotten to renew the old one, ahem :blush:
Then Sunday a good 120 mile + VMCC run. All good, bike is running pretty well. But, before Sunday’s run, I was doing a little maintenance and replaced some dodgy, (that is rather crisp ! ) connectors going to the RITA ignition box. These connectors were straddling some diodes, old small black square Lucas ones that when I searched on the 'net seem to have been for 1970’s car headlight wiring. MGB’s and the like. Taking a look on the 'net suggests that diodes are fitted when using a pair of coils wired in series. The previous owner of my bike fitted a Japanese twin output coil. Do I need these diodes at all ?
Cheers, Tony.

Are you sure these are Diodes?. I think they will be Ballasts. The RITA ignition will work with a good quality dual output 3 Ohm 12V coil with a 1.5 ohm ballast.

Hi, according to what I have found on the 'net, they are described as diodes. Here’s a link to some on eBay : http://www.ebay.co.uk/itm/MGB-Lucas-Diode-In-Line-Headlight-Relay-Circuit-83225-RD-953048-Leyland-Jaguar/391649838242
I guess I should at some point check the coil to see what resistance there is. At the moment she runs ‘ok’, there is snatching at low speed, though I am 99% sure it’s because of backlash in the drive train rather than a misfire. She idles ok and when on the throttle goes like a rocket ! I just wanted to check that I didn’t have something in the electrics that really didn’t, or shouldn’t be there.

i would dump the system completely and upgrade to a more modern crank mounted ignition… as these older systems get less and less supportable you may get stranded


Third attempt at typing a reply! (problem typing spaces)

I’ve had two Ritas, neither had ballast or diodes. 2 x 6V coils in series. I think the diodes were for 2 x 12V in parallel. If you’ve got a single Jap 12V with 2 x HT outputs then I think you can junk the diodes. But first ensure the primary coil is 3 Ohms or greater. But I’m assuming they’re not in circuit?


Yes they are, next time I have the seat and tank off I shall measure the coil and probably remove the diodes. I know the PO had problems with the bike, he did virtually zero miles in the time he owned it, and I think he said the last motorcycle shop that worked on it were the ones that swapped the coil. So I guess they wouldn’t even have noticed the very small black diodes in the wiring.
I would love a new ignition system, but have too many more urgent projects I am working on, so the Guzzi will have to make do with basic fettling for now.

I was looking into fitting a Rita system when I had a Lario and that certainly suggested that there should be Diodes in the circuitry. Never worked out what they were for as I sold the bike on.
Diagram here

Not sure either, bike has done around 1150 miles since I bought her, and box not gone up in smoke (yet), so I guess I won’t worry too much :smiley:

I have a RITA system on my Spada, with 2 x 6 volt coils in series. No additional bits and bobs.
I believe AO Services can repair the later units, and have some of the older ones for sale. Their website also has some circuit diagrams and fault-finding information.

Just looked at Don’s picture, which shows 2 x 12 volt coils in parallel, with diodes. Maybe the diodes stop back EMF feeding back up into the box?
There are 2 kinds of RITA box I think, so maybe different?

Hello, To confirm these are diodes. To test switch on ignition and put a multi meter set to 20V ish. Measure the forward voltage across the diode it should be 0.6-0.7V. If it is a ballast it will be a lot more can and the voltage can be measured either way. Ballasts are fitted to AB5 modules and the AB11 there is no ballast. Rita information: http://heskethownersclub.org.uk/technical/LusacRitaGeneralInfo.pdf Just before I posted this I saw the diagram supplied by Don Spada. Ok these ARE diodes and as Ranton Rambler correctly identified these protect the switching power transistor from back EMF generated within the primary coil and effectively increase the sharpness of the disconnection of the primary when triggered. This will result in a greater secondary voltage being generated. If these are faulty I suspect the bike will run but the spark will not be so strong. In other words don’t remove.

Re the diagram, yep that’s it. Without the diodes the 2 coils would interfere with each other.

If it’s a single coil now, then I can’t see what the diodes are doing. Wild guess, only one is connected between coil and amplifier.

Nothing wrong with Rita if it’s working and set up properly, usual problems are “dirty” connections due to its age, in fact I cut out the 5-way connector block on my one and soldered the wires together, the terminals were decidedly brown. (Originally bare brass.) And put new 1/4" connectors on the other wires.


Actually no, they separate the primaries of the 2 x 12V coils in parallel, otherwise one coil or the other prevents the other from making a spark properly, how do I know I tried it with 2 12V coils just wired in parallel and that’s what happened.

and effectively increase the sharpness of the disconnection of the primary when triggered. This will result in a greater secondary voltage being generated.

Again no they don’t, it actually depends on how fast the transistor switches off.