In article <199510241528.IAA23887@scn.org>,
bc620@scn.org (Ernest G. Janzen) wrote:
> Perhaps; however burnt exhaust valves are most often caused by setting the
> exhaust valve clearance too tight or by too lean a fuel mixture.
I check/reset the clearances once a year - they should be OK.
Regretfully, I never made a note of which way the clearances went,
however. I distinctly remember *some* of them increasing due to rocker
shaft wear.
Valve seat wear alone will of course cause a decrease in clearance
- an evil circle, obviously.
> A lean a fuel mixture may give good fuel economy but too lean a mixture
> allows a lot of supper heated Oxygen to flow past a hot exhaust valve
> burning the valve.
Yes. But my PI system is definitely on the rich side. It registers
rich when set up according to spec, and becomes even richer when
engine vacuum decreases due to wear.
Indicators like plugs and carbon deposits point toward a rich mix. Of
course there is always a chance that it might have been lean where it
matters most, at WOT. But the fuelling setting for WOT mode (no vacuum)
corresponds to the fuelling curve end stop, and *that* is definitely
not disturbed.
> Remember,
> your Triumph probably doesn't have a modern fuel system with an oxygen
> sensor and computer to automatically increase the fuel to oxygen mixture
> by sensing too much oxygen in the exhaust gas.
But it is very easy to install an oxygen sensor (lambda sond) in the
exhaust system to get a rich/lean indication brought to the dash.
Just drill a hole and weld a nut over it as high up (i.e. hot) in
the exhaust system as possible. A standard unheated g.p. Bosch sensor
may then be screwed right in. The voltage from the sensor (0 to 1V)
will then indicate the rich/lean, with approx. 0.7V corresponding
to stoichiometric.
The information I've got indicate that the sensor will be very sensitive,
and really only will be useful for indicating rich/lean.
I will be installing such a device real soon now, and can report my
experiences later...
Egil
--
Email: egilk@oslonett.no Voice: +47 22523641/92022780 Fax: +47 22525899
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