Trying to set the carburator and can't get it to run smooth. Had it tuning great then next time I went to use mower it was exactly the same as before I had it running great. First pull and it starts but goes off right away. Then have to hit prime to keep it running. Cleaned carb , lines, and tank then it ran great again for 15-20 minutes then idol up and down up and down then off and won't run again.