change the inline fuel filter. It doesn't look like there's grit in there, but I bet there is. cheap.
Next put new fuel in tank after draining old fuel.
Now if the plugs are wet, you might want to check the spark. Are there any lose or broken wires on the coil?
Pull the dist cap and see if there are any frayed or marginal wires in there.
Put it all back together.
Have someone crank the engine with a screwdriver stuck in the ignition wire end and ground it to the engine or spark plug. Look for a spark.
Or you can get an inexpensive inline light that will show spark strength. BTW, USE A INSULATED SCREWDRIVER WHEN YOU DO THIS AN DO NOT TOUCH ANY METAL. (if you do, you won't do it a second time.)
Do this with each plug also.
Make sure your ignition wires are tight on the dist cap and coil and plugs.
get a manual.