guru repairs

Ignition System Trouble Shooting.

Last time we discussed how magnetic fields cause current to flow in wires. The current flow is then harnessed to make the spark plugs work.

Now we will discuss how to trouble shoot this system.

First of all the system consists of:

-A flywheel with a magnet

-A magneto with a main coil and a switching coil

-An On/Off wire

-A spark plug and spark plug wire.

That’s it.

In the olden days you had a switching circuit called points, but I will not bore you with that. I have several old motors that have points. (If you are really interested in points I will write an article about trouble shooting those…but not today.)

So what’s the problem?

The problem is that I was riding my go kart… blew the chain… made a massive clunk…engine still ran right up until I shut it off. I replaced the chain and now it won’t start.

What do I do? Cry? Uh…No…

First off all look at the system. So the engine not running must be symptomatic of

-No Gas

-Flooded (too much gas)

-No compression

-No Spark

-Switch is off!

So yes, I checked.. there is gas. (check!)

The engine has nice resistance and compression (no thrown rods, no loose valves, everything is tight…) (check)

Yes I checked it was ON! Also I removed the off wire from the switch near the engine. Still nothing. (check)

Pulled the spark plug out and tested for spark:

No Spark:

The possible causes for no spark are:

Faulty Spark Plug (ie short circuiting because of ash contaiminents, broken insulator, too much gas on plug)

Or a faulty ignition mechanism

Well I cleaned the plug well. Used a different plug…

Note: But you know what I should have done first? I should have taken the plug wire and tried it against the engine. Well I tried that too: no spark.

Not looking good here… What do we do next?

This is where stuff starts coming apart.

Understand that the system involves the flywheel, so we need to access it and see if the flywheel is okay.

By “okay” I mean the following:

-Is there a magnet in it anymore?

-Did it get damaged? (very unlikely) Check with screwdriver: does it stick? (check, yes there is a magnet)

The next critical thing is to check the keyway. 8 times out of 10 the key gets sheared. This can occur from sudden stops of the engine. A sudden stop can occur from various reasons such as a broken chain grabbing hold of an activated clutch. An instantaneous shock load can be introduced into the system.

The other way an engine can be come jammed suddenly is if the rod blew inside, or the engine ran out of oil (seized up).

Next time…. What happened to the ignition system?