The first thing I would check is the float. Is it stuck from varnish? If you know how to remove the carb and clean it, I think the only part you'll need is carb cleaner.

I couldn't say for certain what the cost would be. You will have to poll some machine shops in your area to get a feel for the prevailing rate. Automotive machine specialist type shops will be the best to check with as they have the equipment and expertise to handle a job like this. To them, it's actually an everyday event to cut a cylinder head for oversize valves in the quest for more power. Doing the same to an engine block (in your case) to correct for damage is not all that different, for them.

Ok , I have I believe to be a 2011 Craftsman riding mower with a 48 inch cutting deck and a 24hp Intek V-twin Briggs & Stratton engine that was given to me 3/25/18 of this year. Engine model #446677 0463 E1. Previous owner said engine started backfiring while mowing then died. Since I had done auto mechanic work for several years and the mower still looked almost new I accepted it. Got it home and charged up the battery and give it a whirl. The engine completed about 4 or 5 revolution’s and it backfired. So did a little research on this issue. Found out it could be several things. So I removed the flywheel and checked for a bent flywheel keyway. It was fine. Next I pulled the valve covers and what do you know. Sitting on the mower on the left side it had dropped the pushrod out of the lower exhaust tapper and sucked it into the engine. The valve guide and spring looked fine and were not stuck as I could compress the spring and valve without any hard spots. On the intake valve it had about .0012 clearance and the pushrod was barely hanging on. The right side of the engine was almost as bad finding both pushrods barely hanging on and not dropping out of the tappers. I have tried to use a telescoping magnet and run it inside the engine just to the right of where the pushrod sets on the lobe. I’m not sure if the pushrod is steel or aluminum? Anyway no luck from that point of entry. Next I removed the oil filler tube and went from that angle but the magnet only grabbed the crankshaft and wouldn’t allow me to move the magnet all around in the crankcase to retrieve the stray pushrod. It got dark on me so I had to stop for the night. Tomorrow I’m going to drain the oil and remove the drain valve and give it a try that way and after the oil is drained I had thought about jacking up the opposite side of the mower so that the pushrod might be loose in the crankcase and slide or roll to the side of the crankcase where the filler tube and oil drain valve are and maybe get lucky and be able to retrieve it. What I would like to know is the exhaust pushrod steel or aluminum and do you have any suggestions that wouldn’t require the engine to have to be torn down ! I sure could use a engine repair manual showing how to separate the engine case if needed to extract the rougue pushrod. Anything you can suggest or can me to download would be awesome. Thanks Tim F.

The "letter" in the above model #'s denotes basic design series. They may be extremely similar, or they might be as different as cast iron bore vs aluminum. 777 1st Vertical 2nd Plain bearing 3rd electric start. The TYPE number identifies the engines mechanical parts, color of paint, decals, governed speed, and Original Equipment Manufacturer. This could also include the alternator capacity/output wiring, among other things.