Jet replacement Wear should gasket go

the jet action of the unit is dependent on good quality blades on the impeller
Sand , muddy water , plastic, weeds all affect the impeller and wear down the blades
what you describe indicates an impeller to housing clearance wear problem from one or all of the above

When you installed the new jet, did you install a new gasket on the wall fitting or use 100% RTF type silicone?
In order to seal a wall fitting that is cracked an leaking, the replacement must have either the gasket or silicone to seal the wall fitting against the wall of the tub or it will leak when filled with water.
Rod
U S Parts Center

Instructions

1. • 1 Remove the seat by unscrewing the bolts found on the four corners of the seat. Remove the clamps from the top of the air box using a pair of pliers to access and remove the air filter. The air filter is removed by unscrewing the wing nut and sliding the filter out of the box. Loosen the hose clamp that connects the carburetor to the intake manifold, using a screwdriver.
     
   • 2 Loosen the fuel delivery hose clamp with a screwdriver and pull the carburetor out of the Blaster. Before troubleshooting the carburetor, it's important to note whether you've made a significant change in altitude or a change in your exhaust/intake setup. If you've made an altitude change, installed an aftermarket exhaust pipe or modified your air box, the jets will need to be changed. Refer to your manual for specific re-jetting instructions based on your altitude. Your exhaust kit will provide a recommended jetting setup. Do-it-yourself modifications like removing an air box will require you to experiment with the jet setup until you find the right one.
     
   • 3 Disassemble the carburetor by unscrewing the bowl screws from the bottom of the carburetor. With the bowl removed, the float, pilot jet and main jet will be exposed. To remove the pilot and main jet, unscrew them from their respective holes. The main jet will sit in the exact center of the bowl, while the smaller pilot jet will be set just below the main jet.
     Use a blunt object like a stick or rod to push the bottom of the needle receiver assembly out of the carburetor. The needle receiver (which houses the needle jet) will slide out of the top of the carburetor along with the slide, spring, carburetor cap and gasket. The carburetor is now completely disassembled and ready to be inspected.
     
   • 4 Inspect the pilot jet for blockage, slide a thin wire through the pilot jet's hole, spray it with carburetor spray and blow the center hole with compressed air. Repeat this process with the main jet. If there is any blockage or wear, replace the jets. If you have made altitude changes or exhaust/intake modifications, insert jets that correspond to your changes as recommended in your manual. Note that this may take some experimentation with different jets to get the correct jet setup, as there are many jet sizes for different scenarios.
     
   • 5 Inspect the bowl, floats and ports for any signs of debris or gunk. If debris or gunk is found, remove it using a spray carburetor cleaner, soft wire brush, or thin wire (to insert into small orifices). If no gunk or debris is found, you've ruled this out as a possible cause for the starting issues, and can focus on the replacement of carburetor components.
     
   • 6 Look for abnormal wearing on the jets, float valve, gaskets, O-rings and springs. If you have not changed altitude or modified your bike in any way, then it is best to inspect these components. Any one of these components, or a combination, may be contributing to your starting issues. You may choose to replace individual parts such as a new float valve, though replacing all the interior components with a carburetor "rebuild kit" is advised. Rebuild kits can be ordered online or through your dealer, and will ensure your carburetor is fully repaired.
     
   • 7 Slide the gasket, spring, spring holder and needle jet assembly back onto the carburetor cap and insert the assembly into the top of the carburetor. Screw the main jet into the bottom of the needle jet assembly by accessing it through the bowl area. Screw the pilot jet back into its hole below the main jet. Clip the float valve onto its hinge within the bowl a insert the bowl gasket. Screw the bowl to the bottom of the carburetor to complete the re-assembly process.
     
   • 8 Re-attach the carburetor to the intake manifold using the hose clamp and screwdriver. Slide the fuel feeder line onto the brass receiver port on the side of the carburetor and slide the air box boot over the carburetor's intake port, which should be facing toward the back of the bike. Re-install the air filter with its wing nut, slide the clips over the air box top to secure it to the box and slide the seat into place. Re-install the seat screws to complete the re-assembly process.
     
   • 9 Prime the carburetor by twisting the throttle once and start the Blaster.
     

Normally gasket has not to be replaced after battery change.But all depends of the use.For example if you wear the watch in salt or pool water and never flash it with fresh, clean water after,it may be a cause of gasket wear.Remove the back cover.Replace all 4 batteries(be sure first that you can do this with extreme caution as all parts are tiny).Remove gasket.Check gasket condition(cracks,gasket too dry and hard).If gasket OK, apply a small amount of special silicon compound for watch gaskets,all around and to all sides of the gasket,put it back in place,carefully.Be sure that gasket is set correctly all around.Put the back cover in place and screw with much caution (not too tight-a little resistance).Your watch now normally is water resistant.But if you want to be 100% sure,take the watch to a serious repair center where it will be tested under pressure ( 3 Atm average).Then they will tell you if your watch is 100% water resistant.

If they replaced the jets, did they replace them with the correct size? First off, the metering jets do not wear. Ethanol does not wear jets. If they replaced them, they replaced them to change the mixture. I would have them replace the jets with the original jets. Now, if something is going to wear, it the "needle jet" which isn't really a metering jet. It's the jet that the needle slides in when the slide in the carb goes up and down. It will wear due to the rubbing of the needle against the inside of the jet towards the engine side of the jet. Again, someone it telling you a story. Ethanol will not wear a brass jet. They changed the jet to change the fuel air mixture and now it's not right.

To find out which way it's wrong, try taking the air filter out of the air box and ride the bike at the speeds you have the problem. If the problem gets worse, you are jetted too lean. If he problem gets less severe, you're jetted too rich. By removing the air filter, you're allowing more air to get into the carb leaning the mixture. Now, since at this speed you are not a Wide Open Throttle, you're still running on the needle in the mid-range of the RPM range. You can lean the mixture by lowering the needle and richen the mixture by raising the needle.

What you need to do is take the bike to someone with an Exhaust Gas Analyzer and a Dyno. They should be able to put the load on the bike exactly like it's on the road and check your fuel air mixture at any given RPM. This will tell them if you're too rich or too lean and the RPM range will tell them which jet to change or the needle position to change.

Ethanol does not wear brass jets. The shop screwed up the mixture on your bike, that plain and simple.

Good Luck
Steve

Fuel Starvation - Float Bowl Carburetor
1) remove air filter assembly
*be cautious of tearing the mounting gasket. If it does tear, you HAVE to replace it. It is part of the priming system
2) remove the float bowl fastener. This is the main jet
3) carefully remove the float bowl, the rubber o-ring/gasket will not be able to be used if it is removed, you WILL have to replace it
4) using a spray 'carb cleaner'
spray up thru the center of the carburetor
spray and clean the main jet with cleaner and 'tag' wire
(tag wire is very thin, and can be used to clean the hole in the center of the main jet)
5) clean any debris from inside the bowl or carb body
6) re-install bowl and center bolt, air filter assembly

*if you need gaskets, your Briggs dealer can supply. The kit is cheaper than individual gaskets, and all the parts needed to finish the above repair are in the kit.

I’m happy to assist further over the phone at https://www.6ya.com/expert/rolandw_c013176d62ee17ae

Fuel Starvation - Float Bowl Carburetor
1) remove air filter assembly
*be cautious of tearing the mounting gasket. If it does tear, you HAVE to replace it. It is part of the priming system
2) remove the float bowl fastener. This is the main jet
3) carefully remove the float bowl, the rubber o-ring/gasket will not be able to be used if it is removed, you WILL have to replace it
4) using a spray 'carb cleaner'
spray up thru the center of the carburetor
spray and clean the main jet with cleaner and 'tag' wire
(tag wire is very thin, and can be used to clean the hole in the center of the main jet)
5) clean any debris from inside the bowl or carb body
6) re-install bowl and center bolt, air filter assembly

*if you need gaskets, your Briggs dealer can supply. The kit is cheaper than individual gaskets, and all the parts needed to finish the above repair are in the kit.

I’m happy to assist further over the phone at https://www.6ya.com/expert/rolandw_c013176d62ee17ae

If you are not running an open or free flowing exhaust go back to the stock size jets but use the DynoJet parts instead of the stock.
DJ jets tend to run bigger than oem jets