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Ben, Ben, Ben....

You can't look at this FI system so simply.    The reason the surge happens is
because unburned fuel in the exhaust causes the 02 sensor to deliver a high
value to the FI computer.   When it gets this high value it runs a default
lean fuel curve essentially ignoring the value of the TPS.  The flipping from
the rich curve to the default lean curve makes the bike surge.   If you ride
it purposely in that "surge zone" you can almost sense this happening.  It's
not just a matter of the bike running lean and needing more fuel poured in.

The trick is to get the TPS set to a value just lean enough to avoid tripping
the O2 sensor.   That's essentially what the 0=0 procedure does for you if
it's done properly.

The reason the 83i Powerbox works is because you unplug the 02 sensor, then
place a jumper in the Cat Code Plug box that makes the bike run this default
lean curve all the time.   You then manually add the amount of fuel necessary
for good running by adjusting the box which delays shutoff of the injection
nozzles by minute amounts.

If you want to put a resistor somewhere, a better place would be in the wire
between the 02 sensor and the computer.   I'm not sure about the voltage value
of the 02 sensor or what value resistor would be effective here, but it's the
02 sensor that causes all the trouble.  There is variability between 02
sensors and sometimes the difference between a "good running" oilhead and a
"bad running oilhead is just the electrical value being put out by the sensor.

BMW solved this with the extra spark plug.  It burns all the fuel in the
cylinders at these low speeds. The San Jose twin spark mod does the same.  The
high 02 sensor value isn't reached anymore.  Result is no surge and better

- -TB

Subject: Re: Add a resistor to TPS circuit?

On Fri, 28 Jan 2005 11:33:21 -0500, you wrote:

>I'm a newbie, but...
>The surging seems to be associated with small throttle openings (but not
>idle... I'm not sure what "idle surging" would feel like) and closed-loop
>operation with the O2 sensor contributing its 2 cents worth.
>One fix is to twist the TPS, thereby fooling the ECU into thinking the
>butterfly is more open than it really is (and thus fooling the ECU into
>spritzing more gas into the mix). But that's a pretty blunt instrument and
>enrichens the mix all through the range.
>Folks at ease the basic math and a soldering iron, might suggest that adding
>a resistor in the circuit with the TPS potentiometer could influence the
>small-opening voltage but have rather less effect on the larger openings.
>Anybody tried that? Anybody know the resistance value of the TPS pot?