bigchill, well said!

I guess I'll just have to do the usual........adjust, drive, adjust, drive, etc.

Kirk,

Start closing the bypass, the idle will slow, then lean it out accordingly. Do this when the engine is warm. Do it in slow small steps to get you idle down. Remember how much you turn the screw. Reducing the bypass requires that you "lean" it out by turning the idle mixture screw CCW. Race the engine between settings and see where it settles.


Final "field" idle setting...when you've gotten your idle down to 1000RPM, lightly push up on the air plate (or lever). if it stumbles you are new too rich. If it races, you are closer to lean.

Adjsut accordingly.

Souk,

Thanks, I'll give that a shot.

I must be missing something here. The bypass that sets the idle speed just bypasses the throttle, not the metering unit, right? If the mixture was correct, then it shouldn't need to be adjusted. Reducing the bypass does not affect the mixture, does it?

Maybe I see the reason. An overlean mixture can be sustained with a higher airflow rate. As the mixture is brought into spec,(richer) the idle speed will race, and the throttle bypass will need to be closed some more. Of course, this is sortr of the opposite of Souk's scenario.

Jerry Kroeger

soux,
you described this particular field setting method to me a couple months ago. i tried the method out and based upon my subjective determination of what was happening at the stage of lifting the plate, i decided to lean the mixture. after about 6 weeks i checked my plugs and determined from their more whitish appearance that i appeared to be running lean. my thoughts are that i either over-adjusted the mixture (quarter turn) or i just didn't interpret the test correctly (maybe it was fine and i was 'looking' to make an adjustment). my point is i think this method is probably accurate only to more experienced tuners. i rarely have had need to adjust mixture in a couple of different p-cars, so i'm hardly one who has developed a strong feel for it..i'm quite sure i can get a car running decently and in the ballpark..just not to the degree that you can without benefit of a gas analyzer (in other words, props to you). i'm still suggesting that if kirk's level of 'tuning' is more comparable to mine than yours, he would be better off having a shop do it unless he can get supervision from someone else more experienced than he while he learns your field method. does that make sense? while your description of the method sounds fairly straightforward, i still think it requires a certain degree of experience to interpret what will be subjective results.
ryan

I'll start a new thread....

Here:

http://forums.pelicanparts.com/porsche-911-technical-forum/232089-cis-idle-speed-mixture-setting-without-analyzer.html