Atco 1748 still no spark

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Will
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Atco 1748 still no spark

Evening all,

When I got this mower I replaced the points with an electronic ignition module and obtained a weak but fairly consistent spark, however not enough to get it going.

As I like the mower and it's one I fancy putting into service I've purchased a new coil for it, at the horrendous price of £85. 
 

Now I have no spark at all. What's going wrong?
 

Any help gratefully received.

Will

 

 

 

wristpin
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Are you running the original

Are you running the original points and condenser with the new coil or using the electronic trigger module? If the latter, have you kept the original flywheel position to tdc.  Best to set the  timing with the points in place then turn to tdc and make your own reference marks to use when installing the trigger module. 

Will
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Hi Angus, yes I've been

Hi Angus, yes I've been extremely careful to time it correctly, crank notch at 12 o'clock and the marks lining up flywheel to backplate. 
 

I know you can't properly test a coil without an ignition tester but, using a multimeter, this new coil gives virtually the same reading as the old one (set at 20k ohms)

DJD
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I've fitted quite a few of

I've fitted quite a few of the Mecon etc power transistor type switch modules that claim to fit many engines and do away with both points and capacitor. You need the points still fitted of course to ascertain exactly when they open and to do so when density of magnetic flux is at its highest point. By all means do away with the capacitor (condensor) but make 100% sure that points are not being shorted out when they're open, or you'll never get a spark, check wiring and any switches in circuit also.

Modern digital meters are not good around old magnetos, the magnetic waves and intermittent AC voltages and currents play havoc with them.

I hope that helps.

wristpin
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One characteristic of the

One characteristic of the after market  Meco and  Nova Trigger units, and for that matter the OEM Briggs Magnetron units, is that they seem to require a greater cranking speed for the initial fire up. I frequently fit Mecos to Villiers F12 Slopers and it is difficult to get a spark by just flicking the flywheel when checking ones work during reassembly - easy to achieve with points and condenser in good condition and properly set up.

A year ago, for the first time ever I had a Sloper on the bench fitted with Villiers OEM ( Wipac) electronic ignition and had more or less convinced my self that it was faulty . Only when I spun it with a mains electric drill and got a steady stream of sparks, did I change my mind. After final assembly it still needed a more determined pull on the rope than a points equipped F12.

Quite what the above proves, I’m not sure, so just regard it as an observation . However, buried somewhere in a Briggs manual they do publish rpm figures for the greater rpm required to fire a Magnetron equipped engine compared with the original points and condenser design.

 

 

 

 

 

 

Will
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Thanks for the help people!

Thanks for the help people!

This has the makings of a very frustrating job.

With the new coil in I could not get any spark whatsoever. Nothing. So I swapped the old coil back in and hey presto a consistent spark as before. So I am assuming the new £85 coil is duff?

So I have a spark, timing is spot on, and compression is 60 psi which compares favourably with a midget engine I have which is a good runner. Also the plug is wet so fuel is getting through.

What does surprise me is that I can get no life out of the mower at all. Not even a cough. I can only imagine the spark is not strong enough to ignite the mixture? 
 

thanks all

 

DJD
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60 psi is not a lot, even for

60 psi is not a lot, even for a two stroke, try putting about a half thimbleful of oil into plug hole and whirling engine over without plug in, then try starting it up, the oil will seal the rings to bore better and increase the compression until the engine fires, a trick that I use quite a lot on old bikes.

wristpin
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I presume that at that price

I presume that at that price the coil came from one of the legit suppliers so may be its time to have a word. Have you put a meter across the primary and secondary ?

Will
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Thanks again.

Thanks again.

Re the compression all I can say is that the midget engine (also on meco module) runs like a trooper with similar psi.

yes - I've put a meter across the primary, and it reads 3.75 set at 20k ohms. The coil that was in the mower when I got it reads 3.25, the coil in the midget engine reads 7.something 

I bought it from Villiers services 

will

 

DJD
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Sorry to butt in but that's

Sorry to butt in but that's not right, are you saying the primary winding is reading 3.75 ohms or 3.75 thousand? I doubt you'd be able to read 4 ohms on a 20K ohms scale, unless it's a digital meter? Reading should be only a few ohms at most, with everything disconnected of course, like the points and capacitor. The primary windings are so thick (like a darning needle) that they hardly ever give any trouble, only at the connections then.

It's the secondary coils that hold the important information or readings, they can be shorted out or open circuit, meaning a break in the wire itself, expect anything from 5 thousand ohms to about seven thousand.

Digital meters are no good for working engines with all the magnetism and AC variables flying about, a good, old fashioned now, analogue instrument is so much better and works with them all. With an analogue on X1 you are reading the actual scale itself, what could be simpler?

Will
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You've found me out DJD,

You've found me out DJD, electronics is not my strong suit :)

I am indeed using a digital multimeter, I've just ordered an analogue one from Amazon.

Using the digital meter for the moment set at 200 ohms the new coil gives a primary reading of 0.6, and with the multimeter set to 20K ohms, the secondary gives a reading of 3.7K ohms.

Using the same settings the coil that came in the mower gives a primary of 1.5,  and a secondary of 3.25K ohms

on the box from VS is says 'coil sprayed in protective coating, clean terminals with wet and dry or similar to ensure good contact' Although I've cleaned them up with emery paper I'm beginning to wonder whether this might be the root of the problem

 

wristpin
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Might not just be the

Might not just be the terminals that need a clean. If there is not a a separate earth wire from the coil windings ( just the HT and LT wires) it will rely on the contact between its core and the stator pole pieces to complete the circuits . If that is the case check clean the two ends of the core with solvent ( don’t attack them with emery reducing their fit in the pole pieces) and check the continuity to earth.

 

 

 

 

Will
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Thanks Angus, I'll give it a

Thanks Angus, I'll give it a whirl tomorrow.

Will