Spark problem

[alands]

Hi
This has got me stumped.
I have a spark on both plugs when they are not screwed into the ports.if I screw the plugs in even just finger tight I lose the sparks.if I take them out I get sparks again.
Anyone got any ideas as to what is the problem??

[donnybach]

How do you know the spark is lost when screwed in apart from not firing? An earth fault would cause it but seems unlikely on two plugs.are your leads insulation failing?

[alands]

Hi
Thanks for the reply.
Ive
Taken the plug caps off and held them against a earth and they spark fine when no plugs in,They even spark down the plug holes when the plugs are not in but as soon as i screw the plugs in the spark goes.
Ive checked the coil and it is within spec.
Ive checked the pick up and it is within spec.
Ive cleaned the battery to earth lead
Originally had no spark from the cdi so ive purchased a cheap one and now have a spark but with this problem.
How can creating some compression in the bores make me loose the spark?

[donnybach]

Weird, tried another set of plugs? Is there another cdi you could try from a mate or club? Is the spark trying to fire at the correct time/position?
Does the engine have a good earth back to battery neg?
My mate has a tdm with issues but I’ve not got to see it. Might be a common issue

[alands]

Tried loads of plugs,same issue.
It does have a replacement pick up and generator.(fitted before i got the bike)
I have not looked at them yet but as i said ive checked the pick up and it was in spec.
How do i check if it is firing at the correct time?

[donnybach]

Just with a timing gun i suppose, while cranking. Not done one for a long time so rusty.
Just a thought, are the leads on the correct cylinder? I’ve not had to think about things like that on my single.

[alands]

I don’t think it will be anything to do with the timing as it is making a spark when not under compression the problem is no spark when under load.
Both leads are sparking when put again the cylinder head.

[donnybach]

So no plugs fitted, the end of the lead itself or a fitted spare plug, held to the casing, sparks. (Try with a plug on but hold the lead to the casing to see if she shorts).
With both plugs in and not connected to the leads, the lead held to the casing (or another plug) won’t spark?

Can’t see how compression would ever affect this unless the plug was damaged. If it was sparking to the casing when the plugs (not connected) were in, I’d say the lead was earthing to the casing not the plug.
If, when spare plugs are in (not connected), you get a strong spark with a plug earthed to casing, and the lead can’t be shorted to the casing, I’d have to suspect it’s firing but at the wrong time.
If I couldn’t get her to go, I’d start from scratch testing every item and connection as per the book. Then suspect the new item if it was still playing up.

[alands]

Hi
Both your first two points are what is happening.
The third point not too sure we are on the same wave length.
Let me try again to explain.
With no plugs screwed in i get sparks from both leads whether it is just the end of the leads or with the plug fitted.
Then once i screw some spare plugs into the head no spark on either lead when testing it against the head castings.
So loosing spark as soon as i screw the plugs in.
Remove the plugs and spark return.
Like you say HOW can it loose spark by just fitting the plugs!!!
weird

[donnybach]

That’s the weirdest fault I’ve heard.
Can’t see how the pressure would cause anything, unless somehow it’s affecting the stator/pick up, the only things inside the casing.
Got a feeling it’ll be something simple but not obvious until it’s found.
I won’t sleep for weeks until this is figured out.