It means it was tested under regular conditions for 50 hours with passing emissions.
Is your exhaust pipe the catalyst exhaust?
Compliance and Certification are two different words,mind you.
You can get an engine to be compliant.
Certification takes a lot of money. A LOT of money.
And a certified engine that is certified for a year before it is sold needs to be re-certified for every unsold engine you have every year so if you're not selling over a thousand engines a year it's a waste of money.
Compliance can be said with a sticker.
And the reality is that anyone can generate a sticker.
Certification I'm hearing needs an actual engine stamp not unlike a VIN stamp on a car.
This is with some research I've gathered. Sorry. I lost some of the links. I'll find it all again.
Here's a little something from the EPA website. And this talks about non road engines like garden trimmers and such. I can't seem to find that link as to actual cost it's so frustrating. Then there seems to be no link from that site that explains any bike engine kits. I'm sure I'm missing it.
http://www.epa.gov/EPA-AIR/1998/January/Day-27/a941.htm