FIP upper speed range adjustment screw

[jcochran@cox.net]

Hi,
 I am having an issue with my recently restored February 1967 250SL in that my air/fuel sensor shows a lean condition at 80 MPH+ but adjusting the  throttle rods or barometric compensator shims makes the mixture too rich at lower speed ranges. Does any one have experience adjusting the upper speed range screw on the FIP? I don't like the idea of going into the FIP but I see no other way to get it to more properly match the intake air at high speeds without making the mixture overly rich at lower speeds. Also does anyone know what the RPM range is on the FIP idle adjustment screw? Is it only when the pump rod is on the stop or is it RPM related? I really appreciate your comments on this.

Thanks,
Jim Cochran

[stickandrudderman]

If you're using a wide band O2 sensor then you should be able to adjust the full/partial load screws on the pump.
There's a reference to it here on this site somewhere.
You should be very methodical by 1st establishing the current position of the screws by counting the clicks to the stop so you have a datum.
It's then just a matter of driving/adjusting/driving/adjusting until you get the required result but it takes time and lots of it.
I leave the back of the pump off and accept the loss of oil and the mess it makes.

[jcochran@cox.net]

Do you know which direction to turn the screws to richen the mixture  at high speed? Is the "Upper Speed Range" screw the one I should try adjusting first or should I adjust the upper/partial in unison. The engine goes to a mixture of 18 or higher on extreme acceleration and settles in at roughly 17.5 at 80 MPH. Does two clicks clockwise on both screws sound about right or do you recomend something else. It would be nice to have some idea of a place to start and please know how much I appreciate your help with this. If it had't been for you I never would have known about these adjustments which are obviously going to have to be made.

Thanks again,
Jim Cochran

[stickandrudderman]

Other have done it long before me.

Read and digest this:

http://www.sl113.org/wiki/Fuel/Injection

It should tell you all you need to know.