I have a Briggs & Stratton 18.5hp motor that will start and run wide open but not very smooth. It will not idle unless I hold the choke about half way out. I have taken the carb apart several times and cleaned it to make sure it's not stopped up or dirty. It runs very jumpy. My next thought might be that the valves maybe out of chack but I don't know.

Any help?

Hi,
Engine numbers help greatly, as does the brand of equipment it is mounted to. Giving too many numbers might be superfluous, but does always help.
Peace,
Clarke