SPARK PLUG BEING FLOODED WITH GAS. STOPS RUNNING AFTER 15 MIN USE. BLOWS BLACK SMOKE OUT EXHAUST. REPLACED AIR FILTER DID NOT HELP.

Hi garydriskell...

Sounds like you have dirt/debris in your fuel inlet valve and possibly have some in your carburetor jets,fuel passages or a diaphgram that is becoming non-flexible.
NOTE: Before you dissemble the carburetor:
Make sure you mark each piece with a awl, or some kind of instrument that will make an alignment scratch before you dissemble the carburetor into separate pieces.
That way you will know which way it goes back together when you reassemble it.

Be sure to check your fuel tank for water and dirt/debris, if there is water/debris then you need to clean your tank.
Also check you fuel line condition after a while they will degrade and need replacment.
Make sure you are getting spark at the spark plug, to do this:
A semi-faulty plug will also cause you problems ,so I suggest that you do the following:
Remove your spark plug and check to be sure you are getting fire at the spark plug.
You do this by grounding the plug on the head of the engine and pulling the crank rope, if you are getting spark then:
Check/Clean/Replace your fuel filter if you have one.
When you remove your fuel line/s from the carburetor be sure to make a drawing to how the line/s are connected to the carburetor.
Also make sure you are using fresh fuel...and oil mix if your using a two cycle mower or weedeater with the oil to the right mixture and not too much oil as it can cause hard starting.
If the mower/weedeater is over a couple of years old, then I recommend that you buy and install a new carburetor repair kit,because the diaphragm will get hard and that will cause it to be hard to crank.
I recommend that you use a laquer thinner type cleaner to clean and dissolve the laquer build-up in the float and needle jet passages.
Be sure to remove all plastic and rubber parts before using the laquer thinner because it can dissolve the plastic parts and render them unuseable.
Be sure to use compressed air to blow out all the fuel and air passages.
Be careful when blowing out the passages, because there are sometimes small rubber type seats in the bottom of some of the passages.
Sometimes you can get by with priming the carburetor or using starting fluid and letting it run a few times like that and it will flush the gunk out of the jets,but most of the time you will need to rebuild the carburetor.
Keep in mind that the float (if you have one) for the carburetor must be level when you go to reassemble the carburetor or follow the instructions you get with the carburetor kit.
When you clean your carburetor and remove the jet screws, you will first need to lightly seat the jet screws.
But before you lightly seat the jet screws count the number of turns it takes to seat the jet screws from their original position.
Be sure to mark the turns down on a piece of paper.
That way when you put the jets back in, you know to lightly seat them first and then turn them back out to their original position before you started.
Once you have your carburetor rebuilt that should solve your problem.
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