On Sunday 24 October 2004 7:28 pm in rec.boats Mr Wizzard wrote:

Surely someone must have some insight to this total mystery ??
I've been working on small engines, and specifically 2-strokes
for a long-long times, so this unsolved mystery has been having
a huge inpact on my life (and my shop, my time, and everything else).

Back to basics, you need:-
a) Fuel in at the correct fuel/air mixture
Check the carb and the inlet port. Some inlets
have reed valves. Do you get equal suction on
both cylinders.
b) Initial compression in the crankcase
This is the one that people forget - 2 stroke
engines must have crankcase compression. Check
for gaskets, seals, and broken reed valves.
If in doubt replace the reed valve, they do
tend to wear out and not seal.
c) Transfer to the top - I have never seen a blocked
transfer port but some idiot may have fitted the
wrong piston or fitted the piston the wrong way.
d) Final compression
Measure this with a compression tester
e) A good spark at the right time.
Check the timing. Use a new plug, lay it against
the block and check for a good fat spark at the
electodes before fitting.

In my experience most obscure 2 stroke problems are due
to some kind of crankcase leak, but check all of the
above before tearing down the engine.

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