Gas leak out or the carburetor

turn off fuel valve if still leaks its between valve and the tank should be two lines from tank to valve or tank itself or even valve --if stops then leak from valve to carb ---either way need to remove valve knob and side flaring to access area

Clean the carburetor, line, and fuel tank with Gunk engine cleaner. Check for broken or damaged tank or fuel line, loose hose clamp, loose carburetor, or carburetor sediment bowl. You may need a new carburetor gasket.
Hope that this is helpful

Gas leaks? You didn't provide many details. If you mean leaks from the tank then it's probably a faulty gas line or tank, which wouldn't be to hard to fix. If you mean leaks from the engine then you have a bigger problem. Either way you are looking at a fire / injury waiting to happen. Before taking it to a repair shop, check the fuel line, tank, air and fuel filter, and most importantly the carburetor. When they malfunction the engine gets the wrong air/fuel mixture which can cause stalling - sputtering - flooding etc. If you're not sure, take it to a shop to be fixed, a few dollars isn't worth the risk to you or your house. Grimm

Without know the specific engine I would say the carburetor float float valve seat is leaking. Usually a carburetor cleaning and rebuild usually fix this it leaking out the carburetor.

Now with some engines the gas tanks are two piece plastic that glue together that leaking over time and need replacing.

Either way you first must determine where the leak is.

There could be a couple problems. 1 the fuel tank may have a leak.
2. The connection(usually a hose) between the fuel tank and the carburetor could be cracked or faulty
3. There could also be a bad seal in the carburetor that is letting the gas leak out.
check those out first. I would put some gas in it and then see where it comes from.

Nat, the gas is likely leaking from the carburetor, primer system or broken fuel line. I recommend contacting your local authorized service center for assistance.

You may contact the manufacturer, download manuals, check fuel/oil ratios, order parts, find your local service center, and view other resources using these links:

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User manuals
What is the correct fuel mixture for McCulloch products Chainsaw Trimmer...
McCulloch Service
McCULLOCH PARTS ACCESSORIES

I trust this information has proven beneficial.

Is the gas leaking out of the tank? Is the gas leaking from the carburetor? Where is the gas going? There have been issues related to the brass seat in some of the carburetors. The fuel leaks internaly in the carb. and "spills" over into the crankcase. This is noticeable by gas in the oil when you remove the dipstick. If this is what is happening, you would need to have the needle and seat replaced in the carburetor or replace the carburetor itself whichever is easiest. Hope this helps in some way.

fuel leak best to start at the tank check around the tank seems for gas residue check you fuel petcock for leaks fuel line leak,carburetor for leaks.
if there is nothing you find externally you may have a stuck float or bad needle seat allowing fuel to seep into the engine cylinders and into the exhaust pipe.

There's a fuel block under the tank that splits the single output from the petcock to four lines to the carburetors; a cracked or broken line or a damaged block could be the source of the leak. There's also a fuel level sensor on the underside of the tank that can leak and cause the same problem. A cheap diagnostic tool might show you the source of the leak:
mix powdered clothes detergent with water until it's a thin paste, add red (or any other bright color) food coloring to the paste, paint paste all over areas that may cause the leak (in this case, you'd paint all the fuel lines to the carburetors, and the entire underside of the tank). Drive until leaking gas is noted, check for missing colored paste.