Are you using a 72mhz system? You need to answer some of these questions or no one can help. If you are using a 72mhz system is there metal to metal contact at the carburator?

For example is the throttle arm itself made of metal combined with a metal clevis. This was a very common reason for for this behavior on 72mhz systems and people forget that metal to metal at this point is a big no/no.

John