OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Two Stroke Trimmers & Brushcutters Echo SRM-200DA no spark

I've got an old Echo that I'm restoring. It has a rather bizarre spark problem. If the 'Off' line is disconnected from earth, no spark. If it is connected to earth, still no spark. If a nail is inserted into the Off line connector and held a couple of mm from an earth point, a spark will jump between the Off line and the earth and at the same time a spark is produced at the spark plug.

When I brought this trimmer home, something hit the Off switch and broke it (I've taken it off and just left the line). It originally had a connector for the Off line and it's body earthed to the trimmer chassis. As there appears to be little wear to the electrical system (looks almost new) I'm wondering if maybe the On/Off function worked by creating a spark within the switch (which in turn causes the spark at the plug) rather than a traditional short-to-earth. Does anyone own one of these or have any idea of whats up? Any help is appreciated.

Qwerty, I understand the appeal of the explanation you've come up with, but it seems rather unlikely to me. It implies not only that your kill switch is a 15 kV switch, and the kill wire a piece of HT ignition lead, but also that the operator of the machine is supposed to be in constant danger of near-electrocution whenever it is running. I suggest that some other explanation is more likely to be the correct one.

What happens if you isolate the kill wire back at the ignition module?

Bear in mind that the kill wire is supposed to ground the base end of the coil primary, so when it is grounded, the switching system cannot ever isolate it from ground (which is what triggers the spark). That would mean it could experience the peak voltage across the ignition capacitor (often called the condenser in the old days). That peaks at 150 Volts or so. You might get a small spark from that voltage, but not a blue 5 mm arc, as you get from the secondary. If you are getting a nice blue spark, as long as the one you get from the spark plug lead, from your kill wire, then it sounds as if there is an unwanted connection between the primary and secondary of your coil. This could happen, for example, if the grounded end of your coil secondary had ceased to be grounded, and was flashing over to the sometimes-grounded end of the coil primary, which is the same point the kill wire connects to. If that has happened I think you need to replace the coil, preferably before someone gets hurt.

I'm guessing that you mean to disconnect the kill wire where it terminates (between the points and the condenser, I think) in case it's shorting somewhere. I was testing continuity on cables with a multimeter (don't worry, not testing spark with it) and found that even when they are separated, there is constant continuity between both of the spark timer points. Is that normal? I can't see it being so as it has to complete a circuit for a spark to fire. (I think this might mean that the condenser can never charge enough to produce proper spark).

Thanks for all your advice... it has been very helpful.

I'm not clear on what you mean there. I think you mean that your resistance meter shows a finite resistance across the points when they are open. It inevitably would, because of the capacitor across the points, which has to charge before it could show open circuit even if it didn't leak, which it probably does. The charge time for the capacitor might be very long indeed if you were using a digital voltmeter, which has a series impedance of 11 Megohms.
Edit: On top of that, the points are for DC purposes, connected across the coil primary, so the primary resistance of a few ohms is the highest reading you could get even if you disconnected the capacitor.

Your capacitor might well be faulty - they were usually the least reliable component in the ignition circuit - but I can't see that causing high tension voltage to be applied to the moving breaker point. That point is only connected to the capacitor, and the earthy end of the coil primary. The earthy end of the coil secondary is supposed to be earthed to the coil frame.



If the secondary has lost its ground, it may be possible that it has somehow (probably due to arcing) connected itself to the primary, which might cause approximately the symptoms you have. It would also cause gross arcing across the points, and would gut the capacitor in short order.

When I meant 'continuity' I meant checking for closed circuit. The multimeter has a diode continuity test that makes a buzz noise when the probes are connected electrically (such as touching both probes to a metal bar). I didn't check for resistance as I figured whatever figure the meter would provide wouldn't provide any insight to what the problem was (as your post explains), but you answered my question anyway (about the open circuit.).

So, do you think I should put a whole new electrical system in, or just replace the cap and see if that makes a difference first?

I think I should also mention that the spark on the kill lead does not look very potent (or enough to be HT) as it is a tiny light orange spark rather than white/blue. I get a similar spark with other trimmer motors that are working fine, when the kill switch is broken and the lead must be earthed to stop the engine).

It is normal for the kill wire in a points ignition system to have a peak voltage of hundreds (say 150-300 V) which is enough to produce a visible spark, though not a very long one - certainly not 2 mm.

So, I am back to not knowing what you are unhappy about. With the kill wire isolated (i.e. not shorting to earth, or anywhere near earth) does the magneto generate a spark from the plug-wire to ground? (Don't use a spark plug, in case it is defective.) If it doesn't, you have an ignition fault, but most likely an ordinary one. Most such faults are because the breaker points aren't correctly gapped or the capacitor is faulty. The remaining few are just about certain to be shorts to ground or defective coils.

There is no spark on the HT even if the kill wire is isolated or earthed. Ignore what I said about 2mm, redid it and it's under 1mm.

Can the cap be easily replaced? I have a couple of spare caps from other trimmer engines... buying a new coil or original cap is out of the question, as most spare parts sites want $40 for the cap and $60 for a coil!

The ignition capacitors are somewhat standardised in terms of capacitance (usually 0.1 to 0.3 mFd) but vary somewhat in packaging and mounting provisions. The penalty for using the wrong capacitance, within that range, is that one or other contact will pit while the other one develops a corresponding mountain. Usually small engines do not run enough hours for this to be an issue. Hence the use of a capacitor from another broadly similar magneto should work. (Famous last words, of course - you may turn out to have some oddball ignition system I haven't heard of.)