Repairs Craftsman B&S 19.5HP Surging Problem

[JDViper]

I have a 98 craftsman that is having some running issues. It seems to surge up and down at all throttle speeds. What I have already checked:
New plugs
New fuel filter
Checked for good fuel flow
Replaced old gas with new high octane non ethenol gas
Bypassed existing fuel system to double check it was not a fuel supply issue
Cleaned the carberator twice (cleaned good too)
All carb passages verified for clearance
Installed new carb rebuild kit
Checked for vacuum
Rebuilt fuel pump
It still has the same surging since i started working on it. It starts fine, then revs up then down til it just about starves, then back up. It will run fine with the choke and about half. Any ideas or input will be very helpful.
Thanks!
Model # 42E707
Type # 2631 E1
Code # 9810145B

 

[mechanic mark]

Object moved click anyway, replace diaphram at carburetor. Replace air filter & adjust valves per manual. https://www.youtube.com/watch?v=1-XlET33VHM

Post craftsman model number from under seat.


Information:Object moved

 

[JDViper]

Object moved click anyway, replace diaphram at carburetor.

I did a total carb rebuild including the fuel pump. Could it be a coil issue? That is one of the last things to replace...

 

[ILENGINE]

The fact that is smooths out with partial choke, almost without a doubt comfirms a partially clogged idle circuit in the carb. does the engine smooth out if put under load, like engaging the deck.

 

[JDViper]

Yes it still runs rough.
I did notice that when I cover the small inlet under the fuel pump it clears up. It looks like this is an "Idle mixing valve". After doing some digging, it looks like some carbs came with a screw here and others didnt (later models).
5212.5 questions, electric and carb - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
Im thinking I should just get a used carb and start from scratch.

 

[EngineMan]

Parts manual is showing that the carbs are fitted with Jet-pilot, for the 4-screw fuel pump mount carb part number is 693508, and for the 3-screw fuel pump mount carb part number is 691431.
If you believe that it shouldn't have one, then the hole should be fitted with a welch plug.