It won't idle or idles high.
Hello. It sounds like you are experiencing either an ignition timing problem or an issue with the carburetor. Most of the time if the engine runs fine at higher speeds, this is caused by a carburetor issue. The throttle plates may be worn or the jet may be failing. I would typically run through a process called propane enrichment which helps me to determine if the problem is within the carburetor. If you were looking to have this fixed, I would recommend having a certified mechanic inspect your high idling issue to verify what needs to be repaired.