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The bike can run with no continuity through the cap because the spark generally has enough power to jump the gap. The same way it jumps the spark plug gap.

Try to clean the end contact inside with the resister, spring and screw in fitting removed. It may just be dirty but there is a right angle brass strap running through the right angle of the cap that appears to fracture.

Initially this likely isn't a problem but the longer it goes on the more the gap will be spark eroded increasing the gap and making carbon. This means they get worse over time and given long periods of inactivity likely that corrosion also sets in.

If you can't get continuity you will need to replace the caps.

David Silvers sells them with and without resisters.
 
Discussion starter · #22 ·
The bike can run with no continuity through the cap because the spark generally has enough power to jump the gap. The same way it jumps the spark plug gap.

Try to clean the end contact inside with the resister, spring and screw in fitting removed. It may just be dirty but there is a right angle brass strap running through the right angle of the cap that appears to fracture.

Initially this likely isn't a problem but the longer it goes on the more the gap will be spark eroded increasing the gap and making carbon. This means they get worse over time and given long periods of inactivity likely that corrosion also sets in.

If you can't get continuity you will need to replace the caps.

David Silvers sells them with and without resisters.

Once unscrewed the brass cap from the pipes, both presented a film of carbon inside but the left one had some carbon dust in. None of them had a spring inside.
The odd thing is that the left side is the one that probably caused problems in the past given that the left igniton coil has the black film removed so, probably, was a spare part from another bike or was ripped apart to be fixed.
Do you think that this type of erosion could be the cause of the problem?
Is it possible to completely disassemble the pipes to replace the resistors inside (if they are gone)?
 
This is what the inside of your spark plug caps should look like


When you unscrew the connector (brass part that attaches to the spark plug) the resistor, spring and rod should come out like this. Some of them have shorter rods and longer springs but the arrangement is similar.
In order to work reliably the parts must all be clean enough to make good electrical contact, including the place inside where the spring makes contact.
 
Discussion starter · #25 ·
This is what the inside of your spark plug caps should look like
View attachment 219884

When you unscrew the connector (brass part that attaches to the spark plug) the resistor, spring and rod should come out like this. Some of them have shorter rods and longer springs but the arrangement is similar.
In order to work reliably the parts must all be clean enough to make good electrical contact, including the place inside where the spring makes contact.
View attachment 219885
I've disassembled the pipe and this is what came out:

The resistor has no continuity and i didn't find a way to get the spring out (yet).
Can you tell me which type of resistor should i buy?
@CXPHREAK the test you were suggesting is to check the spark "in a visual way" or should i ride with the spark connected this way?
 
Unfortunately the resistors have never been sold separately. Fortunately, complete new caps are available from David Silvers and a few other online sources.
 
Discussion starter · #27 ·
Unfortunately the resistors have never been sold separately. Fortunately, complete new caps are available from David Silvers and a few other online sources.
I've read that exist some spark plugs that carry an extra built in resistor and so, as someone mentioned before in the post, a mod with a brass rod is possible. I've alao read of ngk upgraded pipes but i didn't understand in what the upgrade consists...
Which is the best option?

Coming back to the igniton coils: should i put them in the oven and test again or am i fine with the hair dryer test that i made?
 
The brass rod modification is not an upgrade, just a way to keep it running if you can't get new caps. Some resistance between the ignition coil and the spark plug gap increases the duration of the spark event so that the fuel burns more completely. You can change to resistor plugs and non-resistor caps (or caps with brass rods in place of the resistors) but by 1981 they came from the factory with both resistor caps and resistor plugs in parts of the world where radio interference was a bigger concern (like Canada).

I have successfully cleaned and rebuilt spark plug caps a few times over the years (most recently I put the insides from some other used caps I had into the ones on my CX) but none of them were as dirty/corroded as yours. If mine looked like that I would order new caps
 
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