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Plug spark at startup, testing #713280
10/31/17 12:29 am
10/31/17 12:29 am
Joined: Dec 2006
Posts: 3,893
Massachusetts, U.S.A.
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btour Offline OP
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Massachusetts, U.S.A.
T120R 71

This goes along with the hard to kick start thread.

So, the thought is that perhaps the coils are not up to snuff. I know the plug needs more juice to spark under compression. The plugs do spark when out. Bike runs fine after startup. But perhaps there is not enough when starting. If the inline led gizmo is lighting does that confirm that the plug is firing?

As I remember, the distance the spark should jump should be 3/8 inch. Is that correct? I realize that this does not confirm that plug will spark in the cylinder. It is just an indication.

I can perform both tests.


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
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Re: Plug spark at startup, testing [Re: btour] #713352
10/31/17 2:23 pm
10/31/17 2:23 pm
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JubeePrince Online content

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Originally Posted by btour


As I remember, the distance the spark should jump should be 3/8 inch. Is that correct?


Not sure about 3/8", but the proper gap on a plug to run is 1/40"

Steve


'77 T140J
"Vintage Bike". What's in your garage?

"The paying customer is always right."

Fitting round pegs into square holes since 1961...
Re: Plug spark at startup, testing [Re: btour] #713354
10/31/17 2:44 pm
10/31/17 2:44 pm
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btour Offline OP
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Got em gapped at .025, Steve. They came out of the box set a big larger. They used to come out dead on. No change in behavior from old plugs, so I guess that was not the problem. I mean faulty plugs.

Now I am trying to determine if they are sparking in the cylinder with kick start. I did search, and confirmed that "in the air", using adjustable gap tool, the spark should travel 3/8 inch.

Thank you.


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
Re: Plug spark at startup, testing [Re: btour] #714354
11/09/17 8:19 am
11/09/17 8:19 am
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Pleasant Hill, California USA
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TR7RVMan Offline
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Hi Bob, I don't know about the actual air gap the spark can jump.

However, On bikes running points, I've seen many Triumph spark plugs out of bike during kicking. The gap is indeed supposed to be .025". Visually the spark looks weak. Not a strong crack like on modern cars or even old cars. Yet the bikes start & run perfectly with this seemingly weak spark. If bike starts & idles, I doubt spark is the root problem.

I've never tested spark with Boyer or the like.

Don


1973 Tiger 750
Re: Plug spark at startup, testing [Re: btour] #714357
11/09/17 8:40 am
11/09/17 8:40 am
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Christchurch NZ
R Moulding Offline
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Are the coils not new ones?

Rod


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Re: Plug spark at startup, testing [Re: R Moulding] #714375
11/09/17 1:40 pm
11/09/17 1:40 pm
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btour Offline OP
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Originally Posted by R Moulding

Are the coils not new ones?

Rod


Coils are new 6 volt.


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
Re: Plug spark at startup, testing [Re: TR7RVMan] #714504
11/10/17 3:48 pm
11/10/17 3:48 pm
Joined: Nov 2005
Posts: 7,329
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JubeePrince Online content

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Originally Posted by TR7RVMan

I've never tested spark with Boyer or the like.


Hi Don -

Just in case you ever need to: http://vintagebikemagazine.com/technical-articles/Boyer-trouble-shooting/. wink

Bob - if you can get a blue/white spark out of the plug, that should be (notice the qualifier) sufficient to fire. Yellow spark, not so much. Easy enough to check in a dimly lit area.

Steve


'77 T140J
"Vintage Bike". What's in your garage?

"The paying customer is always right."

Fitting round pegs into square holes since 1961...
Re: Plug spark at startup, testing [Re: btour] #714511
11/10/17 4:31 pm
11/10/17 4:31 pm
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Posts: 3,893
Massachusetts, U.S.A.
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btour Offline OP
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Steve, I get the spark when they are out of bike, but as you know it takes more when they are in compressed area.


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.

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