Mixture question

[brett at netacc.net (Brett Van Sprewenburg)]

Yes, but...that's pretty much exactly what I just said in my first  
sentence. :-)


Here's another interesting tidbit from back in the day, quotes are  
from original:

 >"Competitors in the now defunct SCCA Rabbit/Bilstein Cup racing
 >series (for near-stock, Volkswagen Rabbit sedans equipped with
 >K-basic) used to carefully adjust the idle mixture to a very rich
 >setting-the rules prohibited any real modifications. The result was
 >that the large enrichment in fuel mixture at idle brought with it a
 >smaller but meaningful enrichment at high rpm, where it would give a
 >little more power."

==Brett





On May 23, 2006, at 12:11 PM, Dan Bubb wrote:

> Yes, but......
> As an example, lets say the lift of the control plunger is 1mm at  
> idle and 10mm at WOT.
> You adjust the mixture screw to move the plunger up .1mm. The idle  
> AFR is changed by 10%. The WOT AFR is changed by 1%.
> I have no idea the actual amount that the control plunger is open  
> or moves from idle to WOT, but I imagine the numbers aren't too far  
> off.
> So, considering that the idle adjustment is constrained to be in  
> the range where the engine will actually idle, the amount you can  
> change the WOT high RPM AFR is pretty minimal.
> Dan
>
>
> From: "Brett Van Sprewenburg" <brett@netacc.net>
> Sent: Tuesday, May 23, 2006 11:59 AM
> Subject: Re: Mixture question
>
>
>>
>> On May 23, 2006, at 11:05 AM, Drew Mac wrote:
>>
>>> On 5/23/06, Dan Bubb <jdbubb@verizon.net> wrote:
>>>>
>>>> It's long been my understanding that adjusting the mixture on CIS
>>>> mostly affects idle and has less and less of an effect as the fuel
>>>> metering plate moves higher.
>>>
>>>
>>
>> Yes, this is the case (idle mixture affected more so then high rpm
>> running).  Here's an excerpt from an email I wrote back in December
>> of 2000:
>>
>> From the Bosch Fuel Injection book chapter 5, section 2.1 "Mixture
>> (CO)":
>>
>> "To ensure that the basic air-fuel mixture is in the best range for
>> emission
>> control, all continuous systems have a provision for mixture  
>> adjustment.
>> Although this adjustment is made at idle, it affects the basic  
>> sensor-
>> plate
>> and control-plunger relationship over the entire range of operating
>> conditions.
>> For a given lift of the sensor plate, the lift of the control  
>> plunger is
>> adjusted to change the amount of injected fuel, and therefore the  
>> air-
>> fuel
>> mixture."
>>
>>
>> Remember this is a mechanical bias adjustment that changes the
>> relationship
>> of the air flow plate to the fuel metering plunger for the entire
>> operating range of
>> the mechanical plate.  For a given volume of air moving through the
>> air box,
>> the plate will "float" to the same height.  Alter the relative
>> relationship to
>> the fuel metering plunger via mechanical means and you've got a
>> change in fuel
>> delivery for a given volume of air at every value of the air flow  
>> plate.
>>
>> So, yes, it alters the AFR throughout the operating range of the air
>> flow metering
>> plate and therefore engine operation.
>>
>> ==Brett
>>
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>