fixed main jet size?

[CowboyPhD]

Is there a visual difference between the adjustable and non-adjustable fixed main jets? I think the adjusting needle was added, but the fixed main jet port was not changed. Is there a way to tell them apart? She idles fine and I can run her up to 1800 RPMs, but after a few seconds she slowly revs up to 3,000RPMs+ and I have to throttle her back down. Would this be consistant with a wrong sized fixed main jet? (Overhauled/rebuilt the carb last week- maybe where jet got switched out with a spare.)

[Don Moyer]

Main jets have small index numbers stamped on them. The standard late model fixed main jet has an index number of 21 and the fixed jet of an adjustable assembly has an index number of 23.

Don