[TR] TR4 engine question

[Randall]

>   I don't see how ignition timing could affect it as 
> it is turned off. 

'Dieseling' is called that because it results from the fuel/air mixture
getting hot enough to burn without a spark.

Running with late timing at idle means the throttle is open farther (for the
same idle rpm), so more fuel/air gets sucked into the cylinder and gets
heated more from being compressed.

That's why the cars with vacuum retard (ie late timing at idle) came
equipped with the anti-runon solenoid. 

Carbon can start to build up almost instantly if the mixture is way too
rich.  Wear in the carb jets & needles can cause the mixture to be rich at
idle even when it's OK at higher rpm.

The fan problem can be solved with a diode (so power generated by the fan
motor can't feed back into the ignition circuit) or a relay (ditto).

Some electronic ignitions are sensitive to the small amount of current that
flows backwards through the ignition warning lamp.  A diode will fix that
too. (My MSD 6A came with the diode in the box and instructions on how to
install it).

Long time ago, I had a summer job driving tractor (mostly towing wagonloads
of potatoes from the field back to the shed for processing).  One of the
things I discovered was that the tractor engine would almost always do
something interesting if I shut the ignition off with the throttle open.  My
favorite was when it started running backwards.  But it was also
entertaining when the engine stopped, but the fuel/air in the exhaust
manifold would light from the heat. Big bang then a pretty blue smoke ring
drifting away.

Also discovered the drainage ditches beside the potato fields were covered
with hemp plants.  Had some little trees too, made a good place to eat my
lunch <g>

-- Randall