"Mungo \"two sheds\" Toadfoot" wrote in message ...
"The Natural Philosopher" wrote in message ...
Its an oldy, but apperas to have bags of compression. Simply was in use,
left up for a winter a couple of years ago, never started since.

Its a ltllet 2-0stroke japanese engine - probably about 25cc or so and I
can;t see any spark - the pllug smells of petrol and we even dribbled
some mix into teh p[lug hole, to no avail.

I whipped off the pull handle and discovered something I hadn't seen
since me dads moped curca 1960. A magneto and some contacts. I adjusted
the gap so it was at least closed some of the time and open some of the
time, but still no visible sparks. I removed the wire off the switch
that stops the thing in case this was faulty, and still no sparks.

First of all, is there some way I can identify that there really are no
sparks? I stuck a car strobe light in series with the plug, but I think
this runs off the LT side of the car not the HT...so probably proves
nothing.


You *can* hold the end of the HT lead while someone gives it a tug. It's not
particularly nice but it won't kill you unless you have a pacemaker or a
weak heart.

Its been years since I fiddled with a magneto, but ISTR that if there is
fuel and a spark these things generally kick a bit and fire if not run.
This ones doing neither.

Is it down to thimgs like stripping out the points and claening them up?


The contacts should be clean and as you say they should open and close. They
should open about 25 thou-ish. Is there a small cylinder anywhere with a
lead coming out of it? If so you might need to replace it.

Si


I still have a cheap timing light that plugged in series between the
distributor and the spark plug, basically a neon as others have
discussed. Only the fancier ones have a sensor on the LT side.

Also a cheap tool that is essentially a neon bulb. You hold one end,
and, I assume, make a leakage path for one side of the neon. Have the
plug in the engine and the lead hooked up. As someone tries to start
you approach the lead with the other end of the tool. As you do so
the neon flickers if there is a spark power in the lead. Don't have
to touch the spark lead for it to detect. These used to be dirt cheap
in auto shops, I have one in the tool box. You can find which
cylinder is missing on a car engine while it is running without having
to interfere with the system.

This tells you if there is a spark getting to the lead. However the
plug itself may not be good.

Take the plug out and attach to the HT lead. Then lay the plug so the
metal body of the plug is in contact with the metal of the engine.
then try it, and the spark should jump. the return for the spark is
through the body of the plug, and the body of the enginge. I have
also used an old wooden pair of tongs my mum used with a top loader
wasking machine to hold the plug firm against the engine.

If you get nice ble zaps you are fine on that side. The fuel quality
is a good idea, also check nothing has dropped off/come loose that is
giving you and air leak on the inlet side, resulting in too weak a
mixture.

Finally check you have no dead lemmings etc up the exhaust. I bought
a 2 stroke bike years ago that someone sold because there was
something wrong with it. Performed terribly, kept stalling, was
impossible to start etc. There was a perforated pipe up the middle of
the exhaust that was completely plugged with coked oil. I had to get
a blowtorch and chisels to get the stuff off and make it pass gas
again. Put it back on the bike and the performance was transformed.

2 strokes are very sensitive to the exhaust.

eric