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1200 RPM in park, 600 RPM in drive.
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Author:  textoad [ Mon Mar 28, 2005 7:40 am ]
Post subject:  1200 RPM in park, 600 RPM in drive.
Ok now that I have a 1000 miles on the newly rebuilt Scamp I figure the rebuilt tranny and engine are broken in. So my son says he has to have the rpm's at 1200 in park to maintain 600 RPM in drive or the car dies. I have checked everywhere for vacuum leaks and I think there aren't any. Whats normal for RPMs with regards to park and drive? Seems like too big of a drop to me. I suspect carburetion but I am also wondering if line pressure in the tranny could be pulling it down.

Specs: 1974 225 .040 over, ported and polished head stock valves, 264 Isky cam, Holley 5200, Lokar kickdown cable, 904 tranny, Hughes torque converter supposedly stock stall speed. 3.21/1 8 1/4 SG rear. Stock electronic distributer with 10 deg BTDC.

Any suggestions would be appreciated.
Author:  SlantSixDan [ Mon Mar 28, 2005 8:03 am ]
Post subject: 
That is a very large drop. Normally with a streetable camshaft you'll see a difference between Neutral/Park and Drive/Reverse RPM of about 100 to 200. So, for instance, 800 in Neutral, 650 in Drive.

This will be an interesting one to figure out. About the only thing I can think of at the moment that might tend to cause this behaviour is vacuum advance. With the car in Park, try disconnecting the vacuum advance hose and plugging it. What happens to RPMs?
Author:  Doctor Dodge [ Mon Mar 28, 2005 8:07 am ]
Post subject: 
Check to see if the vacuum or mechanical advance is "pulling in" when in neutral, that would jump the idle speed way up. The setting may allow the advance to come in and fall-off when the rpms change between neutral and drive.
It may not be the carb, the distributor's advance settings could be causing this.
DD
Author:  argentina-slantsixer [ Mon Mar 28, 2005 9:39 am ]
Post subject: 
could be broken/softened distributor mech advance spring/s, allowing the car to go on the advance side when you're in N or P. Does it feels "nervous" at idling in P or N? like wanting to "gallop" a li'l bit? that would be symptoms of too much advance
Author:  Slant6Ram [ Mon Mar 28, 2005 9:56 am ]
Post subject:  How about...
I was thinking more like a lean idle mixure? I don't disagree with the distributor comments, but it wasn't my first impulse.

Does the problem only happen when the motor is cold or hot, or is it all the time?
Author:  textoad [ Mon Mar 28, 2005 10:28 am ]
Post subject: 
I know it happens warm, haven't checked the cold behavior. Now that you mention it I replaced the distributer vac advance during the rebuilt and I believe the adjuster inside was all the way clockwise meaning the spring was all the way relaxed if I remember right. Whats a good starting point for that adjuster screw in terms of number of turns? Better yet how do you adjust that spring, with the car running or not? I'm pretty sure the vac advance is not coming on because when I set the timing I pinched off the vac line and saw no change with the timing mark using a timing light. However if the mechanical is coming on I wouldn't know it would I. Hmmm :?

Thanks.
Author:  textoad [ Mon Mar 28, 2005 6:11 pm ]
Post subject: 
Ok I checked the timing and it appears I'm getting mechanical advance of about 5 degrees kicking in around 800 to 850. I removed and plugged the vacuum advance to the carb. In park I had my son turn the idle from 600 to 1000 and watched the timing change as it went up. also the vac spring adjust is all the way clockwise so I backed off the screw until I could feel the spring inside getting tighter. Just wanted to make sure the advance was fully off.

When should mechanical advance start kicking in? This is a 30 year old distributer and may need new or different springs. Also which springs are recommended? I believe I read here there are different colors.

Thanks.
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