From MopedWiki

Preface

In some cases where one is not able to, or does not desire to, replace their Gurtner AR series carburettor, the following is a procedure which will allow one to use common Dellorto 5mm jets in a Gurtner carburettor. This procedure is offered as a proposed repair and has not yet been tested for road worthiness, so procede at your own risk.

Tools Required

1. flat blade screw driver.
2. vice
3. drill, preferably, drill press.
4. 11/64 drill bit
5. 23/64 drill bit
6. 1/8 NTP (#27) Tap
7. 5mm Tap
8. hack saw
9. file or sand paper
10. pliers

Procedure

1. Remove main jet

2. Drill main jet to 11/64 about 3/8" deep

3. Tap jet to 5mm

4. Cut the threaded portion off of the jet

5. Smooth rough edges with file or sand paper

6. Insert Dellorto jet in to threaded portion of the Gurtner jet.

7. Wrap tape around your 23/64 drill 5/8 from the point.

8. Drill main jet cavity until tape is flush with cavity opening.

9. Tap carb body to 1/8npt. Cut about 1/4" of threads.

10. Clean all parts of metal shavings!

11a. Install the new jet.

11b. If you so choose, you can damage the OUTER threads of the Gurtner jet (now an adapter) so that it will stay in the carb body once installed, this will make changing jets easier. Here is the adapter "locked" in to the body.

12. Install a 1/8npt pipe plug available at any hardware store, thread sealer may be necessary.