[Diy_efi] A/F mixture, EGT and engine damage

[Adam Wade]

--- Tim Marsteiner <tmarstei at yahoo.com> wrote:

> I get some surging at lower speeds and
> some pretty high EGTs. A/F seem to be all over the
> place(~14.5:1 - ~17:1).

Chances are that you're not getting similarly
homogenous mixture from cycle to cycle, and that this
accounts for both your surging and your fluctuating
AFR.  If the fuel is not well-distributed, you'll be
down on power and get excess O2 in the exhaust, as the
burn will only be in the richer part of the intake
charge.  V-twins, especially at lower engine speeds,
are notorious for having poor repeatability in terms
of intake "tumble"; I suspect that this is what you're
getting.  And then there's the issue of reduced intake
pressure and cylinder filling as the throttle is
closed in increasing amounts.

Unfortunately, the only real way to attack that kind
of a problem, AFAIK, would be changing the design of
the intake tract and/or the piston crown.  There may
be some relief from moving the injector, or switching
to an injector that has a better spray pattern or
finer misting of the fuel.  Using fuel with a lower
pressure of vaporization should also help in that
regard (i.e., avoid "winter" fuel formulations, avoid
ethanol, etc.).  You might want to call Russ Collins
over at RC Engineering and have a chat with him,
sending him a set of injectors for his evaluation. 
I'll bet he could help you operate in that AFR range
with far fewer drivability issues.

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