Bob: Here's the original msg from Howard:
"Max backfires when not running ..I have a 85 vmax 42000 miles stock machine
after it sets for a week or two I turn the ing switch not intending to to
start the bike it fires on one cyl. may not be the same one every time .if
the intake valve is open on that cyl it is heard thru the intake tract or
exhaust pipe if the ex valve is open running the one or two times a week it
does not occure doesn't seem to bother anything..Do the plugs fire when the
ing switch is turned on only?? Thanks Howard.."
Some notes to the other guys who responded:
Phil wrote:
"...and when it is shut off the back fire is happening from
the heat of the residual gases exploding...."
The explosion occurs when the bike is turned ON, not OFF! There is NO heat
at all most of the time, but it has happened when the bike is still warm.
TC wrote:
".... I am simply interested in figuring out how there
can be gasoline in the cylinder/s anyhow after a couple of weeks ...
and the only thing I can think of is a plugged fuel bowl vent ... "
I've thought about this a bit more, and there may be another way for fuel to
be present...
Consider that one cylinder will occaisionally stop (when the bike is shut
off) at some point in the compression stroke with both valves closed, but
fully charged with air/fuel mix. This cylinder will probably leak down after
some time, but will still contain a whole bunch of gasoline vapor. When the
bike is switched on some time later, this cylinder fires, but without much
ooompff. That's the way mine sounds when this happens - it's not a real big
backfire and isn't very loud.
Why does that cylinder fire is the root question here, right? There must be
some charge being stored somewhere while the bike is off, or it's happening
at the instant the key is turned on. Right to the plug...
-CC
VMOA 1162
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