How tightly should a spark plug cap fit?

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prv

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My otherwise-excellent 2hp Suzuki 2-stroke had some trouble last summer which I'm reasonably sure was ignition-related. The system generally looks in good nick, the only questionable thing is the play between the cap and the plug. It has a rubber seal/boot which normally makes it feel like a very snug fit, but with that removed I've just discovered that the actual electrical connection seems rather looser.

The connector in the cap isn't the coil of stiff wire I've seen on older engines, rather it's a pressed tube with two holes drilled in the sides and an outer circlip with bumps that protrude inwards through the holes. This clicks neatly over the terminal on the top of the plug, and certainly doesn't feel like it could fall right off, but it does wobble a little from side to side. Quite hard to quantify, it needs a wiggle from an experienced hand, but as far as possible via the forum I wonder what people think. Is this normal, or could it be the cause of my misfiring?

Pete
 
Wiggle is bad, but I wouldnt blame it for a missfire, you wont get a big enough gap to stop the spark. What could happen is erosion of the connector cap and spark plug top, both very not good.
 
A multimeter's continuity test between the spark plug tip and the ignition while wiggling the plug cap around should tell you if there's a problem. As will black marks from arcing at the top of the plug connector. Most likely it's not an issue - mine's attached the same way and wobbles with the rubber boot removed, but with it it does not and contacts fine.

I've just fixed my Suzuki up. Its ignition troubles (complete lack of spark) were solved by replacing the magneto/ignition unit (all in one and cast into resin), although that was a DF 2.5 4-stroke and may not be the same for older or 2-stroke models.
 
Yngmar said:
I've just fixed my Suzuki up. Its ignition troubles (complete lack of spark) were solved by replacing the magneto/ignition unit (all in one and cast into resin),
Click to expand...

Interesting. Were there any external signs of failure? Mine is similar, and looks good as new apart from some very slight rust under the heads of the bolts that hold it on. But if it can fail internally despite a pristine exterior, then that might be my problem. No signs of arcing in the plug cap as far as I'm aware, so I was probably clutching at straws there...

Pete
 
prv said:
Interesting. Were there any external signs of failure? Mine is similar, and looks good as new apart from some very slight rust under the heads of the bolts that hold it on. But if it can fail internally despite a pristine exterior, then that might be my problem. No signs of arcing in the plug cap as far as I'm aware, so I was probably clutching at straws there...

Pete
Click to expand...

Nope, looked okay apart from a bit of rust on the magneto core laminate. It also measured less than 1 Ohm resistance between stop button connector (stop not pushed) and ground, while the working replacement had about 30 Ohms (from memory - definitely significantly more than the broken one anyways). It never ever made a spark though, which is different from misfiring.

Mine looks like this:
$_57.JPG
 
might be worth checking the screw-on cap on the spark plug for corrosion on the thread or looseness, too.


Ideal place for some Contralube.
 
Yngmar said:
Nope, looked okay apart from a bit of rust on the magneto core laminate. It also measured less than 1 Ohm resistance between stop button connector (stop not pushed) and ground, while the working replacement had about 30 Ohms (from memory - definitely significantly more than the broken one anyways).
Click to expand...

Ok, sounds promising. Mine looks very similar although not quite identical. I'll test the resistance shortly. Presumably the laminations count as ground for a reference against the stop bullet?

Pete
 
sarabande said:
one piccy is worth a thousand wordies....


That's the screw-on cap (or ferrule :) )
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Ah - I have to admit I'd never realised that that part unscrewed :)

No, it's all present and in good order, a new plug as specified in the book (although the old one seemed fine too, but they're not expensive and I wanted to rule out everything I could).

My ignition coil reads 30Ω between stop connector and the laminations unfortunately. But then my trouble was intermittent whereas Yngmar's was terminal, so perhaps it would be less conclusive.

Pete
 
prv said:
Ah - I have to admit I'd never realised that that part unscrewed :)
.
Click to expand...
Thread-drift:- It doesn't unscrew on all spark-plugs, that screw- thread is a relic of the olden days when HT leads were sometimes held by a ring terminal and nut, not push-fit.
Re. loose cap, I don't think that would cause misfire. Again in the past, introducing an air-gap by holding the HT lead a little distance off the plug terminal would sometimes get a reluctant bike engine to start in the first place. There was even a gadget that would do this called the Norton Ignition Supercharger!
 
prv said:
My ignition coil reads 30Ω between stop connector and the laminations unfortunately. But then my trouble was intermittent whereas Yngmar's was terminal, so perhaps it would be less conclusive.
Click to expand...

Indeed - it wouldn't even start. I've got my (used) replacement from "midlandsoutboards" on eBay, who also list a 2 HP Suzuki one: http://www.ebay.co.uk/itm/outboard-Suzuki-2-hp-ignition-coil-/262133923825

May be worth a try, if that's the right one. If it turns out it isn't, you can probably sell it at a profit by getting the rust off and listing it with the proper Suzuki part number, which is easily looked up :)
 
Yngmar said:
Indeed - it wouldn't even start.
Click to expand...

Mine would go fine when it was happy, and refuse to start when it wasn't :). Sounds rather like Nick's Yamaha.

Looks like a replacement CDI unit is on the cards, as I'd originally assumed before I found the "wobbly" plug cap.

Thanks all for the advice.

Pete
 
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