Small Engines (Lawn Mowers, etc.): Surging B&S 8 HP, speed jet, surgin

Question
I have an older 8HP B&S engine on a snowblower. This is not the original engine. I can not find a model # on it anywhere. I looked evenywhere on it. even stripped and repainted it thinking someone painted over the #, but none on the shroud, block or anything.
It uses an updraft type carb and from the investigating I have done I think it is a type "8N Carb"
And from what I read the lower needle screw is common to tear out the threads when you remove the entire assemble from the bowl for cleaning, so I am hesitant to attempt this. (It happened on the first carb I had)
The engine runs well, idles perfectly, but under load it surges badly. I was going to clean the carb but am faced with the above problem. I setup the governor linkage according to a document I found.
My second thought is a weak governor spring. Am on on the right track here?
As far as the needle valves. Can you give me a simple description on what the two control, and the "Initial Setup" setting. e.g. set screw "A" to 1 1/2 turns out....

Answer
The initial setup is correct...1 1/4 to 1 1/2 turns out from a GENTLY seated position.

It sounds like the high speed circuit is not suppling enough fuel under load.  The main source of fuel under load comes from the high speed circuit, the needle on the bottom side of the carb.

Have you tried removeing the needle and blowing compressed air through the jet?

I haven't ever tore all the threads out from the carb, but I have had to drill out the high speed jet and reclean the internal carb threads.  Not that difficult but you have to have some special Briggs taps to clean the carb threads...I think they are 32 threads per inch...not your common tap.

You can slightly seperate the carb halves with the jet in place to drain the carb but you have to be careful not to bend the jet.

I doubt the problem is the governor spring and without the model, type and code number the exact spring can be difficult to locate.  Too weak or too strong of a spring can affect the surging.  My be is most of the problem is in the carb.

How bad did the threads strip out on the old carb?
Let me know.