OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Weak spark and Strong spark, Why is it so?

Hi everyone, I have an old victa utility that switches between week spark and strong spark. When the spark is strong it lasts for quite a while until I stop the engine. The next time I try and start it, the spark is weak, but still there , just enougth to make you feel it but not enougth for a spark.

I repaced the capacitor with something close enougth to the original, cleaned what I think is called the points but I still have the same issue. Sometimes its great ! and sometimes its sad . Very frustrating.

Any ideas or suggestions ?

Thank you for all your help last year.

I see two problems.

"capacitor with something close enougth to the original"

And

"cleaned what I think is called the points"




You are guessing and not sure about what it is that you are dealing with.
Perhaps pictures would help you get the answer you want.

I would assume that its a series 70 motor.
There is no capacitor, there is a condensor.
The points need to be cleaned and set correctly to work.

The whole lot could possibly need replacing. In that case it could be easier to bin the lot and retro fit an electronic ignition module.

Bob, for the record, "condenser" is a pre-WW2 name for a capacitor. The item concerned here is a capacitor, though a special type suited to this kind of service.

Slothland, the points need to have exactly the right gap, and they need to meet parallel to each other. Rotate the crankshaft until the points are at the widest separation that they reach anywhere around the cam circumference, and measure their separation (the breaker gap) with a clean feeler gauge (there must be no trace of oil on the silver blocks that make and break contact). The gap needs to be exactly 0.020".

Variable spark intensity usually means a poor electrical contact somewhere, dirty points, or coil or capacitor is on the way out. When I have had them over the years it has always been a poor contact: bad coil or capacitor gave weak spark all the time (and sometimes no spark). In other words, if I had an intermittent spark (full strength alternating with no spark at all) it was generally a wire (and once, the capacitor had broken its bracket and wasn't grounded, so there was only spark when it touched ground). If I saw dull red spark, I cleaned and gapped the points. If that didn't work I reached for a new capacitor, and if even that didn't work, I replaced the coil. By then it was always fixed.

Here are my thoughts, is the spark weak when the engine is hot? If so I would say something is tempreature sensitive, being either the coil or the condenser.

Thank you everyone for your help. I'll add some happy snaps tonight.

Learn something new every day.
Was more getting at the last bit, suited for service but right part for this particular setup.

That is my understanding of condensers Grumpy, mostly from the interchanging of the terms in documentation I have for some of my valve radio's.

Slothland, If possible could you also make sure to get some shot's of the engine and carburetor, as well as perhaps the serial number (Located on the crank case, near the carburetor, or on the opposite side to the cylinder)

Although quite a rare occurrence, I have seen issues that present like this caused by issues with the cut out, where heat causes a weakness to swell in insulation or cut out assemblies, allowing a very slight pass through, weakening the spark, or casing (more common) intermittent sparking.

It is a very rare occurrence, as the circumstances that cause it are equivalent to balancing on a pin, however, as you will have the camera out, it's not a bad idea for us to know as much as possible about the mower.

Also, How concerned are you with originality, if you want to keep the mower in original condition (It sounds like a mower from the 70's to me) then we will need to make sure all parts are replaced with correct replacements, however, if you have no concern to originality, then it may (depending on the actual case) be easier to replace the ignition with an electronic one (as bob suggested)

Yes, capacitors used in parallel with points in ignition circuits, whether magneto or Kettering (battery/points/coil/capacitor), have a special kind of construction. They have to have a high voltage rating, be physically robust because of vibration, and be able to stand thermal cycling in the presence of moisture. The high voltage rating is because the voltage "kicks back" across the points gap while the circuit is firing. The capacitor needs a 600 Volt rating. Of course it also needs the correct capacity (measured in microFarads), or one or other of the points will erode quite quickly.