Gerald M Van Vlack wrote:
>I'll gladly buy the beer but my question was also how much is too much as I
>expect every engine has some build up especially if they run a bit rich.
>
How much is too much? That depends upon the driveability, and likely any
changes in compression. Every style of engine behaves somewhat
differently because of combustion chamber shape and the way it has been
machined--even how it was rebuilt if it has been rebuilt.
Lots of variables, but the primary one should be driveability. If the
performance is degraded in any way which can be measured, then that's
probably too much. For example, if the car ran fine from the get-go,
but over time, with no change in quality of the fuel used, the timing
has to be retarded to prevent pre-ignition, that's too much. If the
carburetors are set properly, and the idle speed is correct, all other
parameters within specification, but the engine runs on after the key is
shut off, then that's too much carbon accumulated.
If compression starts to vary from normal because of carbon build-up on
the valves, that can have a noticeable effect on smoothness of idle and
low-speed torque. Not too long after Toyota introduced batch-fire
L-Jetronic injection in the early `80s, they found that the number of
complaints over rough idle, in the the period of ownership of two to
three years, increased--especially in areas like southern California and
Arizona where people didn't spend a lot of time driving in the rain. The
modified L-Jetronic system that Toyota used was a sort of batch fire
arrangement where all the injectors fired at once, delivering half the
fuel required once each revolution. The principle was that on one of
those two revs, fuel would puddle up on the hot closed intake valve and
fry off, and mileage would be better because of better vaporization.
What actually happened was that the lighter volatiles fried off, but the
heavier components did not, and they stuck to the valve head, and
gradually cooked down to carbon, which then gave good purchase for more
carbon to build up. Over time, that began to affect air flow at low
speed and more gradually, encouraged carbon to build up on the intake
valve face and seat, affecting compression.
They developed a shop tool which blew walnut hulls through the ports to
clean the valves of carbon and then sucked (most) of the hulls back out
of the cylinders, which worked (sort of). By the time that tool was in
general use, most cars had fuel injection and fuel formulation (mostly
detergent levels) was changed to accommodate that, and the problem
became much less prominent.
So, the short answer--driveability problems with all other settings
correct is the determining factor in how much is too much.
But, doubtful I'll make the Summer Party. Still out of work after 2-1/2
years, and without income coming in, that kind of frivolity sort of cuts
into the food budget. :)
Cheers.
--
Michael D. Porter
Roswell, NM
Never let anyone drive you crazy when you know it's within walking distance....
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