Answering my own question, I just got an email from Genie Customer
Service with the following helpful information:

"To adjust the contact reversing system on your older clutch model Genie.

"Close the door, hold screw slot in rail with a large blade
screwdriver. Use a 3/4" wrench or adjustable wrench to turn the clutch
nut on the motor shaft protruding from the rear of your Genie powerhead.

"Turning the clutch nut clockwise will tighten the clutch and increase
the amount of force the motor will put on the door and visa versa.

"The clutch should be just tight enough to let the door operate both up
and down under it's own power while still being able to reverse itself
from a 2 X 4 placed flat on the floor in the middle of the door.

"If your unit will not adjust properly, you might need to disassemble
the clutch system, clean, and reassemble."

Thanks, Genie!

--ben


On 2009-12-07 06:56:59 -0700, Ben Jammin said:

I recently replaced the springs on my garage door.

Now I need to adjust the closing force on my Genie GXL9900-2 1/2 hp
Screw Drive Garage Door Opener. Although the door opens and closes
freely and clearly by hand, it closes nearly all the way but then
reverses and goes back up when using "Genie". Yes, the safety light
beam is clear and properly adjusted.

On the GXL9900-2 you apparently adjust the opening and closing force by
turning either a nylon nut with a wrench or a metal screw rod with a
screwdriver slot on the back of the unit, unlike the electronic opening
and closing adjusters inside the white plastic "light lens" on newer
units.

I need to know if the nylon nut or the metal screw rod adjust the
closing force and which direction I turn the adjuster, clockwise or
couterclockwise, to increase the force.

I've tried to make the adjustment but it's just too difficult given two
adjustors and two different directions, plus climbing up and down a
ladder to hit the door control button. Got to be a better way!

The PDF manual on the Genie website is for the newer, all electronic
screw drive opener, not the older mechanical opener.

Any help would be most appreciated.

--ben