It is a Briggs engines. Your problems one of two things. Bad fuel or dirty carb or both. You're going to have to take the carb apart again and give it a good cleaning. Get a can of carb cleaner and make sure you clean every hole and jet. Remove the mixture screw on the side of the carb and get that jet really good. That is your idle fuel mixing screw. When you put it back in lightly seat it and back it out 1 & 1/4 turns. This is a good starting point. Also check the float level. Turn the carb upside down. The float should be level. Reassemble and try again. You may have to adjust the idle mixing screw to get it to run steady at low speeds. Old gas or water in the gas will give you the same problems. One question. Does the bolt on the bottom of the carb have a hole in it? If it does this must also be cleaned really well.
I have done all of those things you described above last fall. I completely disassembled the carb and gave it a Chem Tool dip and put a carb kit in it. The carb did have a lot of varnish in it from old gas that had been left in there for a couple of years. (I had given the mower to my mom, as I moved to a bigger yard and no longer needed the Recycler. It didn't get winterized at her house. I am trying to fix the mower so my son can mow lawns with it this summer) After putting everything back together, I could never get the surging to stop regardless of how much tweaking I did to the carb. I finally gave up in frustration and thought the problem must be governor related, and decided to wait until now to tackle it. But before I start splitting the case to replace the governor, I decided it would be prudent to absolutely eliminate carbureation(sp) issues first. Based on things I am reading in this forum and just random google searches, the surging is a carburetor problem. I will go take the carb apart again and check the the holes in the bottom screw/jet. I don't think I replaced the Welsh plug last fall. Does that make any difference?
As an additional clue, the mower runs at slow idle (turtle setting) forever. It is only at fast speed (rabbit) that the surging starts. And, it is intermittent. This is what is driving me nuts. Sometimes the mower will run for several minutes without surging. What is constant is that every time I try to engage the blade, the engine dies. (Which makes it look like a governor problem to me) But if I hold the throttle plate open while I engage the blade, it will run just fine for a while, before it starts surging at some point again.
Thanks for the input to the model number. I found a pretty good engine manual on the Toro website, which includes theory of operation information, which I like. Out of curiosity, I would like to see a clear picture of the governor, so I could understand that thing a little better. According to Toro's website, this is a 5.5 horse engine. I found the engine on the B/S website as well.
Thanks,
Mark