Hey i have recently bought a walbro HDC carb. its off of a homelite XL1 chainsaw (thats what i was told) and want to run it on my ryobi. The carb i had on the ryobi will work better on my stihl engine. The cast in number says HDC 44. I noticed that right near the pulse hole, there is a hole with a screen in it. It looks like it is perpendicular to the throttle shaft. Does anyone know what this is, and does it need crank pressure? I will try and get a pic of it, but my camera is dead

check out http://wem.walbro.com/walbro/family2.asp , and find out all about your carb.
The inner screen filter is the carbs last defense to hamfisted users. It should be clean. If any dirt ever is found there, the tank setup is to blame.
Common errors:
t-line in carb suction line
no filter in carb suction line

The way to do it:
three line tank. One line for filling up, plugged when not in use.
one clunk line with felt filter clunk or sinered element, going directly to the carb.
One vent line, always open

here is the pic:
PS
thanks for that link! Unfortuntely i didnt see the screen that is on the bottom of the carb (i havent torn it apart) I am wondering/worried that it needs pulse pressure. I would take it apart, but the guy at the shop just rebuilt it. The saw that it was on ran good. they were trying to sell it. I would have bought the whole unit, but i dont need an engine laying around that i wont use. right now i have 3 engines, and i will be getting one more shortly.

very exciting! :-)
from the walbro site:

Part Name HDC-44-1
Venturi (mm) 11.13
* Kit - Repair K10-HDC
** Kit - Gasket/Diaphragm D10-HDC
1 * Ring - Screen Retainer 16-42
2 Ring - Shaft Retainer
3 Lever - Throttle
4 Cover - Fuel Pump 21-147
5 Cover - Metering Diaphragm 21-112
6 Shaft Assembly - Throttle 30-634
7 Valve - Throttle 34-48
8 Shaft Assembly - Choke 40-644
9 Valve - Choke 62-40
10 Stop - Throttle 68-13
11 * Valve - Inlet Needle 82-75
12 Seat Assembly - Check Valve 86-520

Hellow PE....It is good to see you still are placing good data on here. I am on vacation in Florida.....but got to get back home in Hesperia Mich to get back to engine conversions...ect. Take Care Capt,n

Well i havent got a reply on whether that screen (to the left of the pulse hole in the pic above) needs pressure or not. I dont have the old manifold, so i cant tell.

That screen looks like a capillary screen that will not flow fuel or air until certain conditions are met and the wet seal breaks. A device like that normally is used either as non-return valve in themain jet, or to provide extra fuel to prevent the saw from speeding up too much.
Hard to tell exactly what it is for without the carb in my hands. I would suggest to block off that screen with a gasket, and see if it works ok.