Plug is Probably OK, but I would check it anyway..
It does not hurt to replace it every year.. As parts go, it is cheap.
The gap could be off and it could be carboned up..
So pull it and check it..
As they sit, fuel that is left in the carburetor can turn to gum and varnish and cause this and other problems.
Also, any gasoline that was left in a gas can for a period of more than 30 days must be discarded because it also has begun to turn to varnish.
More than 70% of all of our repairs in our lawn mower business are due to this same issue. You most likely have dirt, gum, varnish...etc in your carburetor plugging up the small passageways and jets in the carb. It Must be removed from the engine, cleaned very well, any tiny hole, crevice and jet must be probed with a tine stiff metal wire, blown out with compressed air and reassembled using a NEW carburetor rebuild kit. ALWAYS clean the fuel tank and replace the fuel line when doing this repair or you may have to do it all over again. The inside of the fuel line disintegrates over time and these small pieces of rubber will plug up the carb too. Dirt and water from a dirty fuel tank will also plug up the carb. Find the Model, type and serial or code numbers off of the engine and take them to your local dealer to get the carb kit.
First make sure that you have the correct complete carburetor repair kit.
Now take special care when you take the carburetor apart..to make sure that you watch and remember exactly how the gaskets come off.
Remove the float pin ...it just pushes out...and remove the float..carefully.. so you can see how the float needle is attached...(Some of them have a small wire spring holding it to the float....you will have to reinstall this spring when you reassemble the carburetor.
Next...remove the float valve seat. most of these have a screwdriver slot to allow removal. Look around the carburetor and see if it has a small idle adjustment needle...remove this needle if it has one. You are now done disassembling the carb. DO not take anything else out of the carb.
Get a good carburetor cleaner....preferably with a small hose you can attach to the nozzle of the can. Spray the carb cleaner all over the outside of the carburetor. this will loosen the dirt on the outside while you clean the inside. Now spray the cleaner through every hole, and nook and cranny you can fine on the inside of the carb.
When you are finished with the spray,blow all of the passageway clean with compressed air from an air compressor. Also blow all of the dirt from the outside of the carburetor.
Next. Take the entire carburetor to the kitchen sink......Ok maybe it would be better to get a big bowl...so you don't make your wife mad....and wash the entire carburetor with HOT SOAPY dishwater. This is to make sure that all of the carburetor cleaner is completely washed from the carb...(If it is not, you will deform the new gaskets and such that you install...even if it is dry.) Now rinse in clear watter and then blow the carb dry with the compressed air again.
Reassemble the carb using the identical parts out of the carb kit as you took out. install the float seat, then install the float needle and the float in the same position that you took them out. Check the float level after it is installed. Making sure that when the carb is upside down with the float in the up position, the float should be nearly level with the body of the carburetor. Now reinstall the bowl gaskets the same as you took them off. Then install the bowl nut with the small gasket under it. Reinstall the small idle needle if it had one.
There you are done.
Install the carburetor on the engine and you should be ready to go.