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Strada 750 ignition coil

M

mark312

Just got it firing!
Joined
Aug 1, 2010
Messages
5
Hi,

I've just tested the resistance across the +ve and -ve terminals of each coil, as the right hand cylinder has been running erratically for some time. i got readings of 5.0 ohms for the right coil and 4.7 ohms for the left. I believe that normal values for motorcycle coils are 0.5 to 3.0 ohms, which would indicate that both my coils are on their way out. If so, how is it running ok on the left cylinder? Or are these values ok?

I'd be grateful for any help / advice you can offer.
 
Mark, I think expected values are 0.5 to 1.5 ohms, measured from the low tension wire to a ground on the bike.
Also measure between the high tension coil wire and a ground. That should be thousands of ohms.

Sometimes shop manuals will show correct values. And often coils will only show bad reading when they're hot (like when running).

Since both coils are showing similar values, that sounds good. Perhaps it's not them at all.

Joe
 
sign216 said:
Mark, I think expected values are 0.5 to 1.5 ohms, measured from the low tension wire to a ground on the bike.
Also measure between the high tension coil wire and a ground. That should be thousands of ohms.

Sometimes shop manuals will show correct values. And often coils will only show bad reading when they're hot (like when running).

Since both coils are showing similar values, that sounds good. Perhaps it's not them at all.

Joe
Click to expand...

Perhaps you're right Joe - I've just tried swapping the coils over, and it's still the right side (as you sit on the bike) that has no spark, so I'm guessing the problem lies somewhere in the electrics before it gets to the coils. I'm still thinking the coils may need replacing as the left spark isn't bright blue, but at least it's there!

I have a workshop manual for small blocks, but not specific for my model, and there's no mention of coil resistance values. I've tried the Denso website but can't find the exact coil anywhere on their pages.

Anyone any ideas where to look next? (Remembering that bike electrics are a new adventure for me!)
 
Mark, it's not the coils. Must be further "upstream." Perhaps the Digiplex ignition module or a connection between the ignition module and the coils. Examine the wires and connections there.

If they are ok, see if you can switch the connections at the ignit module, between left and rt coils, to see if the problem switches. That will test whether the error is within the ignit module. If that's it, you might buy an old module on Ebay.

You could also switch the system to a modern replacement. A German co. Silent Hektik makes replacement systems, but they are expensive. In the past a replacement system was the Lucas Rita, but I've heard poor reports on it, and it may be hard to get now.

This group on old Guzzi smallblocks has people knowledgeable about your system, you could ask them: http://autos.groups.yahoo.com/group/small_block_guzzi/

And a good electrical diagram done by Carl Allison, can be found on Greg Bender's site: http://www.thisoldtractor.com/guzzi007/sportissimo.html

Hope this helps,
Joe
 
Thanks Joe,

I'll have a look at the ignition module connections when I next get chance. Thanks for that.

Mark
 
5 ohms is fine. Some Guzzis use 3, others 5.

Digiplex or Motoplat? Check all connections and earths.

Change plugs and get new plug caps. Check their resistance. A faulty plug or cap that has increased in resistance can cause the spark to find an easier path to earth.

Just a couple of easy fix ideas.
 
Morizzi said:
5 ohms is fine. Some Guzzis use 3, others 5.

Digiplex or Motoplat? Check all connections and earths.

Change plugs and get new plug caps. Check their resistance. A faulty plug or cap that has increased in resistance can cause the spark to find an easier path to earth.

Just a couple of easy fix ideas.
Click to expand...

This. I've never heard of the Digiplex only triggering one cylinder..
 
Re: Strada 750 ignition coil (edit - the coil is ok)

Hi,

Thanks to Morizzi and Chuck in Indiana for the latest.

I've swapped the ignition control modules over, and the spark changed with them, so I guess that's the issue. To do this, I just unplugged the white connector plugs and swapped them over. The left side had a wire beyond the plug (i.e. on the coil side not the module side) which led to a black cylinder labelled ART with a positive and and earth lead, which I'm guessing from the wiring diagrams I have for other models is a condensor?

Assuming the ignition module needs replacing rather than maintenance, can I fit a module from any similar small block Guzzi, or does it have to be the original? I've done a search for Motoplat but not found anything specific for my model.

Thanks for all your input.

Mark
 
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