Atco weak spark

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1manwent2
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Atco weak spark

I know this has been discussed  before many times but I really have run out of ideas now

I am rebuilding an Atco kickstart 1948 12" It was not running when I received it,faulty coil as usual.

I have replaced the coil and the condenser whilst I was at it,spun it up with a drill,no spark at at all.

replaced ht lead ,still no spark until spun really quickly then really weak

,set points to 12 thou,cleaned and stoned so that are contacting perfectly squarely,any oil or grease cleaned off,insulating bush is on( pre adjusting cam type)

new spark plugs tried,out of desperation I had the flywheel remagnetised which made no difference whatsoever 

Checked all earth connections

if I close the spark plug gap to 10 thou I can get a spark but it's still weak

coil primary is 0.5 ohm and secondary is 5.4k

any thoughts please,I'm desperate

wristpin
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Joined: 23/05/2012 - 22:09
I suggest setting the points

You don’t mention ignition timing.

I suggest setting the points midway , say 13 thou and then  double checking the timing. I’m tempted to say that any spark is a spark . I’ve had plenty of engines that have run quite happily on a puny little spark. Never been a fan of spinning engines with a drill .

1manwent2
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The ignition timing is ok,set

The ignition timing is ok,set with a Buzzetti timing tool,but my main concern is not so much trying to start it yet so much as getting a decent spark as per my other Atco which I rebuilt in exactly the same way.will a weak spark be ok under compression ?

John

wristpin
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I’d never heard of the

I’d never heard of the Buzzetti timing tool but if I’m looking at the right thing it’s basically a means of determining the piston position in relationship to TDC and BTDC; in the case of many two strokes, without removing the head. I have two that I made many years ago using 14 and 18mm spark plug bodies - cheap and cheerful! 

So, while that looks after one half of the equation it still leaves the need to relate that to the opening  of the points - the important bit !  Regardless of whether this is done by the “ fag paper” method or using a multimeter is entirely up to you , but it needs to be accurate. Out of interest has your flywheel got a timing arrow on it and is there a corresponding mark on a boss on the stator?

The text books  say that cylinder compression will attenuate a spark but I can only say that I have never experienced it in many years of playing with engines .  It will be interesting to know where you sent your flywheel for re- magnetising. The only time that I’ve ever done that was in the case of an LD Lambretta in the late fifties and that was not for an ignition issue but in the  vain hope that a bit of extra flux would wake up the resident glow worm that passed for a headlight. To add insult to injury , Lambretta Concessionairs  of Purely Way ,Croydon, lost it, and the new flywheel that they supplied was no better. 

1manwent2
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I'm not over concerned about

I'm not over concerned about actually getting the engine running at this point ,just getting a healthy spark,but I have rechecked the timing The engine has never run in my ownership and is mounted on the bench at the moment whilst I play with it

there is an arrow on the flywheel and a notch on the crank,these were 180 degrees out for some reason when I stripped it down,any idea why?

the remagnetising was carried out by Villiers Services

 

, I

John

wristpin
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The flywheel arrow and crank

The flywheel arrow and crank notch do NOT  line up. The notch is in line with the crank pin so if it lines up with an imaginary line down the centre of the bore the engine is at top dead centre. 

The arrow on the flywheel should be lined up with a a corresponding mark on a boss on the mag back plate when the engine is at TDC .

When Villiers built  the engine they set the points within the 12 to 15 thou range , set the piston to the stated BTDC position and the flywheel to the position where the points just start to open . At that position they tighten the flywheel to the crank. Then they turn the engine to TDC and stamp the arrow  to line up with the mark on the mag backplate.  This is to save anyone working on the engine in the future from having to do the BTDC measuring bit.  So long as you are sure that Villiers Services returned your own  flywheel and not an exchange , that is all that you need to do to time the engine correctly.  Do that and you should have an adequate spark to run the engine.

EDIT

See the attached image