I have a chainsaw conversion engine that surges on wide open throttle. Starts fine, idles great. Not sure of make or size exactly. Only markings are made in usa. Walbro carb. Ive cleaned it already. Thanks

Could be a carb , or coil/spark issue.
You stated that you cleaned it so I assume that you opened the carb and inspected for dirt in the screen. Did you rebuild it ?
What color pump diaphragm is in it , blue,black, tan? Should pull the welch plug and clean as dirt can get in there too.
If the carb is good then look at the coil,spark plug,wire.

I did take the carb down all the way and sprayed with carb cleaner. Dont remember the dia color. The spark looked strong. Ill go inside and look again. Thanks

Also check the carb mount and make sure there are no air leaks.

Geez, I hate to admit how long it took me to find it, but I had my fuel pick up tube crack inside the fuel tank making it nearly impossible to tune the engine. Surging was just a partial list of what I was chasing....

You need to run it with the cowl off to see if the servo isn't at the root of your evil as well.

What and where is the welch plug?

http://outdoorpowerinfo.com/repairs/...wt631_carb.asp

Thats a great link. Thanks!