Technical Articles

Setting the idle on the 912E

By Tony Bray

OK, here it is straight from the manual... Before you start, be sure dwell, timing, and valves are set properly. Also, check for vacuum leaks as they will affect the overal idle quality. Don’t forget the vacuum line connected to the fuel pressure regulator under the air box. At idle when vacuum is highest, it lowers the fuel pressure to as low as 25psi which will affect idle and air/fuel ratios.

  1. Run engine to operating temperature (50°-70°C/122°-158°F)
  2. Connect CO tester according to instructions of manufacturer. Use sepreate tachometers from tester or similar. (OK, who has a CO tester at home? Just make sure to use a good tachometer like those on home engine analyzers. Do NOT rely on the car’s tach as they are notoriously off!)
  3. Disconnect activated charcoal filter hose at air cleaner. (The only hose that attaches directly to the air box)
  4. Take air injection hose off of check valve and insert an appropriate plug in the check valve opening to give a tight seal. (The check valve referred to is below the air filter for the smog pump. If you have removed it, skip this step. If you have it installed, remove the bottom hose and plug the opening at the valve itself. You can use vise grips to pinch off the hose while connected if you hose is still pliable.)
  5. Let engine run at idle and adjust the idle speed on the control screw or bypass screw on the throttle housing to specifications: 925 +/- 50 rpm.
  6. Measure CO adjusting if necessary by taking the plug out of the intake air sensor and changing the CO with the adjusting screw. Turning clockwise enriches the mixture; counterclockwise leans mixture. CO specifications 0.5 to 1.2%. (If you had a CO tester in step 2, do it. Otherwise, you probably shouldn’t touch this screw)
  7. Recheck idle speed and correct if necessary.
  8. Install plug after adjustments.

Caution: Make adjustments as quickly as possible to prevent excessive heat in intake lines.

- Tony
67 912 2.0 Type 4 “Gumby”

DISCLAIMER: These procedures are presented as guidelines ONLY. They reflect particular jobs that were performed by 912E enthusiasts and are offered here as a guide to others who might need to do the same procedure. No representations as to the accuracy of the information contained here is made. The procedures were written to help other 912E owners. These guidelines should always be used in conjunction with a good set of repair manuals, such as those listed above.