Pressure Washer shoots black smoke from exhaust and then will not start
I think the fuel to air ratio is to high (rich)... the engine needs more air. Look to see if you have a choke on the engine and after letting it warm up for a minute, make sure to switch it to run. If the choke is not the issue, then you (probably) need to change the air filter. 

If that doesn't do it, then you may have a problem with the carburator. Don't leave gas in the engine over winter... it causes various problems, including corroding plastic parts- which might lead to gunk in the carburator or worse.