my 1999 carbed hp500's are running rich. I changed out the plugs and still no difference. Tried to play with the carb adjustment screws a little but I dont really know what I'm doing there. how should I troubleshoot this?

Running rich when????? All the time??? at idle????

Could be a powervalve or float adjustment.

What fuel do you run. Run 87 octane. It will burn the cleanest and most completely.

Buddy of mine has the same engine. He has over 400 hours on it, and has had to rebuild the carb twice. You should look into that! How many hours on yours?

Running rich at idle, I changed out the plugs and they're still running rich. At speed they're sounding good.

you have to jet for wide open, so they usually run a little rich at idle. You do have to rebuild them every once in awhile though. I had laz at mesa balancing do mine. when i got them back, i put it on the dyno and the a/f ratios were perfect.

If its only rich at idle then its probably one of a 3 things.

Adjust air bleed screws--the 4 little ones
Bad powervalve---only has 1 inside the front fuel bowl
The float level needs adjusted.

Totally agree, but would like to add one thing.

Air bleeds may need a good cleaning out. These should be cleaned out with carb cleaner atleast a few times a year. Only takes a minute or two.