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a couple of odd symptoms, honda cb350 twin
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the bike's running pretty well, but there are a couple of odd things going
on. i've just recently started riding this bike again after it sat for a
few months - so the carbs may be a bit dirty, and it's probably due for a
valve adjustment.
after an evening ride, i stopped back at my garage to adjust the idle
speed ( to ~1200rpm).
first, i'd noticed a bit of smoke coming out of the bottom of the bike
while sitting at a stoplight. it turns out that this is coming out of the
vent tube that connects to the valve cover. the mist seems to be oil, not
gas - but i can't really tell. it just doesn't smell like gas, and is a
bit slippery. the "smoke" seems to come out in pulses, timed with the
pistons' rise and fall.
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It's blowby. Every internal combustion engine has some. Some more than others.
Modern bikes have it vented into the intake system so it will be reburned. Older
engines had it vented to atmosphere.
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since there are no seals on the valve guide/stem interface, perhaps this
is regular exhaust blowing by through that gap? maybe vaporizing a little
oil on its way through?
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Doesn't sound like a problem.
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second, while i was idling the bike with its headlight off in the dark, i
noticed that the spark plug wires (stock, with rubber caps over the
sparkplug end) are arcing to the cylinder head. there are actually dull
blue sparks from that rubber insulation to the cylinder head on both
sides. has anyone noticed this before?
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Had that happen on my old 360, with the oil coming out the tube. Time for
new rings oversize and piston oversize. That will fix it. Did mine.
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Replace the spark plug wires. You shouldn't get arcing anywhere but at
the plug itself, and that shouldn't be visible with most plugs.
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You need new plug wires. Also check your plug gaps. Larger gaps need higher
voltage to jump the gap, and the voltage will follow the path of least
resistance. If it's easier to jump from the wire to the head, it will do that
and bypass the plug.
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