Need help with adjusting the Air Idle Screw

While doing a long overdue tune up on my '67 bug, I started performing John Muir's suggestion on adjusting the idle air screw. As I back the screw out the idle increases and then eventually decreases. So I work the screw back and forth until I get the fastest idle. The problem I have is that when the idle is fastest I can hear what sounds like an air leak hiss. Is this right or should I get the idle the fastest without hearing this leak. The second issue is that the idle is quick enough that backing off the idle screw all the way does no good. The idle still seams a little fast. Any suggestions would be greatly appreciated.

Reply to
The Highlander
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I sounds like you have a later carb with two idle adjusting screws on the left side. The original carb for the '67 (30PICT1) had 1 adjusting screw (Volume control) on the left and one on the throttle lever. Which carb do you have?

If you have the later carb, this is the procedure to tune it. Later in this message is the procedure for the older carb.

Run the engine for several minutes to permit it to warm up. Then turn it off. Unscrew the throttle lever positioning screw (the one in the back) until the throttle closes fully and the screw just touches the fast idle cam (at the lowest "normal operation" scale), then screw in for 1/4 -1/2 of the turn. This screw is not for adjusting the idle in later carbs.

Then, there are two adjusting screws on the left of the carb. The larger one is the Bypass screw and the smaller is the Volume Control screw. There might be protective plugs over them that you have to remove first. Turn both screws fully in, without tightening them, or you will damage the carb. Then Unscrew the large screw 3 turns and the small screw several turns (about 4). This is to ensure that the engine will idle when you start it.

Now start the engine. Adjust the idle speed to arround 850rpm, using the large (Bypass) screw. Then adjust the mixture with the smaller screw: Turn it in until the engine begins to run erratically or lose rpms. Then turn it back out, until the engine just starts to run smooth and at full idle speed, then continue to turn it out 1 + 1/4 turns more. Repeat the adjustment to the Bypass screw once more to obtain 850 rpm, and then readjust the mixture screw as before, and you should be ready.

If your carb is of the older type and doesn't have the large Bypass screw, adjust only the Volume Control screw as described above, and the idle speed from the throttle lever possitioning screw. If you follow this procedure and you cannot get the carb to idle very low (about 800rpm), then probably the throttle shaft is worn, permitting air to come through and increase the idle speed.

Bill, '67 bug.

Reply to
Bill Spiliotopoulos

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