Idle Rpm High in Park, Low in Drive
Learn to use a piston stop. I still have the one I built in the mid 70's
Remove no1 plug, bump engine to get the piston "down some". Get a socket on the dampener bolt, and disconnect battery ground for safety. You can remove all plugs and make it easier
Rotate engine CW until engine stops against the device. Make an accurate temporary mark below the TDC mark onto the balancer. Clean, tape, marker, etc
Do same thing, rotate engine CCW and make a second mark same as before.
You will now have two marks some distance apart. True TDC is halfway in between. With care this can be as accurate as it needs to be
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If you have breaker points igntion, SET DWELL FIRST before adjusting timing. Wide points gap/ low dwell numbers ADVANCE the timing, while the opposite for worn, "narrow" gapped points.
Make sure to get vacuum "off of" manifold vacuum. Determine where timing should be do NOT necessarily use factory "smogger" specs. Retarded timing aggravates this problem. For a "stocker" I'd run at least 8BTC idle/ initial timing, with no vacuum If you have a hotter cam, look into recurving the distributor advance, and go more, at least 12, in some cases 15-20 WITH A recurved distributor.
A lean carb mixture can aggravate this problem. Look for vacuum leaks, cracked or missing hoses, etc. See if carb mixture screws have affect
Warm engine up to normal temperature, and set idle speed. Adjust mixture screws in/ out to fond a "rough" peak starting point. You want them (to start) a bit CCW or "rich." Best to use vacuum gauge or tach
Adjust each screw, and go back/ forth a couple times. Screw them in "slow" and find closer "peak." After doing that, screw both in until idle "just quite" does NOT drop from the peak RPM/ vacuum. In other words you want the "lean side" of "peak."
Now if it does not 'act" right, and after jigging idle speed in drive, some cars "like" to be final adjusted in drive. I would say this is "fairly rare." BE CAREFUL. Chain rear hitch to a tree, use blocks on all 4 wheels, and or a helper. With trans in drive, "jig" idle speed and mixture for best "in drive" RPM and idle quality
Learn to use a piston stop. I still have the one I built in the mid 70's
Remove no1 plug, bump engine to get the piston "down some". Get a socket on the dampener bolt, and disconnect battery ground for safety. You can remove all plugs and make it easier
Rotate engine CW until engine stops against the device. Make an accurate temporary mark below the TDC mark onto the balancer. Clean, tape, marker, etc
Do same thing, rotate engine CCW and make a second mark same as before.
You will now have two marks some distance apart. True TDC is halfway in between. With care this can be as accurate as it needs to be
==============================================
If you have breaker points igntion, SET DWELL FIRST before adjusting timing. Wide points gap/ low dwell numbers ADVANCE the timing, while the opposite for worn, "narrow" gapped points.
Make sure to get vacuum "off of" manifold vacuum. Determine where timing should be do NOT necessarily use factory "smogger" specs. Retarded timing aggravates this problem. For a "stocker" I'd run at least 8BTC idle/ initial timing, with no vacuum If you have a hotter cam, look into recurving the distributor advance, and go more, at least 12, in some cases 15-20 WITH A recurved distributor.
A lean carb mixture can aggravate this problem. Look for vacuum leaks, cracked or missing hoses, etc. See if carb mixture screws have affect
Warm engine up to normal temperature, and set idle speed. Adjust mixture screws in/ out to fond a "rough" peak starting point. You want them (to start) a bit CCW or "rich." Best to use vacuum gauge or tach
Adjust each screw, and go back/ forth a couple times. Screw them in "slow" and find closer "peak." After doing that, screw both in until idle "just quite" does NOT drop from the peak RPM/ vacuum. In other words you want the "lean side" of "peak."
Now if it does not 'act" right, and after jigging idle speed in drive, some cars "like" to be final adjusted in drive. I would say this is "fairly rare." BE CAREFUL. Chain rear hitch to a tree, use blocks on all 4 wheels, and or a helper. With trans in drive, "jig" idle speed and mixture for best "in drive" RPM and idle quality