After rebuilding the deck over the last two months, now my Yard Machine 600 series tractor will not run properly. The engine will rev and die repeatedly when you try to cut with it. The carb was rebuilt last year and it has new fuel lines and filter. Is this an adjustment problem or is the carb gummed up a little bit since it sat for a few months? This only happens a wide open throttle, but once it does it, it won't stop until you pull the throttle all the way back down. Any help is appreciated. Below is a pic of an exact model as mine.

Was a fuel stabilizer used? Then yes it could have some gummy gas in it, gas starts to go bad after a month. Sounds as though the main jet is clogged a little...

I poured some SeaFoam in it and let it run a few minutes to stabilize and protect the gas and carb... Can I clean the main jet easily? Or does it need disassembling? I have never worked on a carb before... thanks again!

Just take the carb off and clean every little hole with a few shots of carb cleaner... one shot, let it set a second or two, then another... and another... etc. If you ran seafoam, then it can still be either trash or water maybe.

Maybe a carb gasket sucking air

Well, the curious side of me got me into a little trouble. I was looking at the carb after cleaning it and starting slowly taking things apart. I got to the side where the gas line goes in and took that apart. It has a couple of springs and a thin membrane with a larger spring pressing against it. It looks pretty simple. I cleaned it real good and re-assembled it. Now the mower will not even crank. The carb is not getting gas. How cheap are the rebuild kits?. and can you tell me what kind of carb I have (B&S 16.5 Twin I/C) I'll let a real mechanic fix it this time. Thanks for the help again.

The gasket I am talking about in the top right of the picture...

The rebuild kits are cheap, and easy if you remember how you took it apart... lol
One true way to check for leaks is spray carb cleaner, brake cleaner. Etc around the seals, any change will tell you.

It certainly is a carb problem, either some gummy gas/trash or it just needs a new diapragm... the top right is not a gasket, diapragm.

Told you I had never worked on a carb before... I've been watching "How It Works" on Discovery too much... when I first put the diaphram back together, it leaked like crazy... then I re-did it and it stopped leaking... I figured I was looking at a rebuild anyway, so I couldn't really harm it anymore than it already was... do you know what kind of kit I need to get? What kind of carb is on the mower? Thanks again!

This is a pic of my engine...

Diapragm carb, feeds both cylinders... forget the brand though... (actually have about the same engine coming to me to replace one of my engines in a couple days) 18hp apposed. Btw, if you have your model, type, and code... and go to a small engine shop... that's all they need to get the right kit.