Monro tiller spark plug

[charlie]

I have never tested for a spark in the way you describe in the last part of your post ie “Plug cap to plug terminal no light.” All I do is test plug lead to a good earth on engine, then connect plug lead to plug and hold or clamp plug to a good earth on the engine.
You will not get a spark from plug lead (cap) to plug terminal when it is screwed into the engine as there is no earth path, the centre electrode of the plug is insulated from the engine and can only spark across the plug gap. What you are doing is introducing a second gap in series with the plug gap, the attached sketch illustrates this.

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[mitzygolf]

I’ve tried that Charlie but there is no or very intermittent spark but if I just connect the spark tester to the plug cap and the spark tester direct to earth without the plug the light flashers as it should

[andyfrost]

ALWAYS try for a spark DIRECT from the end of the HT lead , if you have a suppressor fitted remove it and check for a spark directly from the end of the lead.

Andy

[mitzygolf]

I’m connecting the tester to the plug cap and getting a great spark to earth do that should all be ok

[charlie]

Yes, if you get a good spark from the end of the lead to earth or at plug when it is out of the engine and connected to plug lead and earthed it should work.

[mitzygolf]

That’s the point I’m getting a great spark to earth without the plug attached but nothing when the plug is attached

[charlie]

“That’s the point I’m getting a great spark to earth without the plug attached but nothing when the plug is attached”
With the plug out of the engine and firmly clamped to and making a good earth contact with the engine you should get a spark with the plug lead connected. If not there is a problem with the plug, what is the plug gap it should be 0.025″
You will not get a spark across the plug gap if the metal body of the plug is not adequately earthed.

[mitzygolf]

I’ve used 2 brand new plugs and the gap is correct. It’s a mystery to me

[andyfrost]

What type of connection are you using from HT lead to plug.

Andy.

[mitzygolf]

Plug cap

[andyfrost]

In that case discard the plug cap and connect HT lead DIRECTLY to plug.

Andy.

[mitzygolf]

It’s a new plug cap and the tester flashes when it’s connected from plug cap to earth. It’s as if the spark is not strong enough to jump the spark plug gap. Could it be the condenser?

[andyfrost]

It could be coil or condenser or points , what colour spark are you getting?? , if it’s yellowish then a component test is in order, are or were your points badly pitted/burnt
Personally I would bin your so called spark tester , they are the most misleading toy you’re likely to waste money on , especially on Villiers ignitions , which it has to be said are notoriously weak.
Yet again , just try connecting your lead directly to the plug and see what happens , remember all early Villiers HT leads had a simple brass direct connector….for a very good reason.

Andy.

[mitzygolf]

Ok thanks

[john-e-w]

Hi Mitzygolf
My Mk3 has never had a plug cap, it has always been (for the past 30 years) a direct brass fitting crimped onto the HT lead and now that I have rebuilt the engine and have some compression, it starts first pull every time – see photo (I hope it’s attached)

John E-W

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