I have a B&S V twin 16 hp engine in my Sears Suburban its a great engine but it had sat for a some time before I got it the carb was varnished I cleaned it and thought it was good mowed with the tractor for a couple of years then the engine would not idle right put on a little choke and it was good go out and mow at full R,s choke off but as some as I'd go to idle it surged I tried cleaning the carb several times by just removing the top because you have to half dissemble the engie to remove the carb every time it would run great for 4-5 hours and then back to the same thing. So after have really good experience with China aftermarket carbs for Kohlers and some Tecumseh's I bought an aftermarket carb for the V twin B&S when I took it out of the box I was a bit worried it had no adjustable jets NONE no the OEM has a fixed main jet but and adjustable idle jet, anyway yesterday I installed it engie started but was surging some at idle but after it warmed up seemed to clear up sso ran the tractorside and drove around at full throttle it would slowly lose and gain RPM's it surged some at idle but then seemed ok. This morning thought I'd try it again the engine started instantly run ok at idle but driving around at full throttle was the same. So really cleaned the old carb now that it was off and reinstalled it this AM started the engine and it ran perfect run it out side ran perfect so I'm hoping I got what every was causing the problem out. Lucky for me I went to Amazon to return the carb and its free return just have to drop it off at a UPS store no packing or labeling.