Determining age of Webers

[Quickstep192]

I just read an interesting post by Paul Abbott where he described differences in how o-rings were used on the idle jets in 1969 and on webers, but that they shouldn't be used in earlier webers. Since I have a problem similar to the one described in that post (popping in transition circuit) I'm eager to determine te age of my webers so I can determine if they should or shouldn't use the o-rings. Can anyone help?

[1976 TN Porsche]

Talk to Paul in person he is a Great guy. Look up his website Performance Oriented or 530-899-8371

[1QuickS]

Check out my Technical web page on my site; there is a picture of o-ring idle jet holders and the earlier versions.

The later versions woth o-rings will be IDTP or if IDA they will have date codes vs. serial numbers. The date codes for IDA carbs will be something like "5D" where earlier IDAs will have numeric serial numbers. IDTP carbs and all subsequent carbs with o-rings will be IDTP with numeric serial numbers or IDA with date codes.

Also, the port where the idle jet is inserted will have a a counterbore ID of about 8mm (.315 or 5/16") to receive the o-ring where the earlier versions have a M6 x 1.0mm thread as the interface; again look to my Technical web page for a photo to identify the differences between idle jet holders. It is fine to use the earlier idle jet holder in a later throttle body but not the opposite as the later jet holder will prevent seating the idle jet when used in the earlier body.