My Briggs 18 hp opposed twin has been running a bit rough, hesitated, and doesn't seem to have the power it did. I swapped out spark plugs, fuel/air filter and no improvement. Warm compression on both cylinders was between 110-120 on both cylinders IIRC. I figured the carb was the next option, and since I'm trying to learn small engine mechanics by doing, I ordered a rebuild kit. I'm a rank novice here. Got the carb all tore down and cleaned up. Ran into two issues 1) I could not get the fuel inlet needle seat out. Evidently you need a self tapping screw, which I didn't have on Sunday AM. 2) The kit did not include the main jet (?) or whatever the name is for the brass jet that sits behind the bolt on the side of the carb. Figured I'd leave the old seat and jet in and replace it later if needed. Fired the engine back up and adjusted the idle screw. The engine purrs a lot nicer now. There is no more hesitation at acceleration - with one exception. When I quickly go from a dead idle to full throttle there is about a one second delay before it catches. But if I slowly run the throttle up, it speeds up like I would expect. So, is the first scenario where it hesitates where I quickly accellerate from idle something to be concerned about? Or is this typical on Briggs twins? I noticed I get a puff of air out the air intake on the carb when it happens. Thanks for the help!