Carbs kicking my !@#$%

[John M.]

67 Tri-power 427/400 powerglide, My RPM in park and in drive at a stop sign is ~750 RPM how come when the car is in neutral the RPM's are over 1K. My main problem is when I put the car in REV. it hits very hard, I thought it might be vacuum until I notice the high RPM at different ranges. I still may indeed have a vacuum leak someplace which could cause the tranny to act the same way. However I think its high RPM when shifting into rev. But it does shift into drive normally, I plan on checking the Mod valve this weekend when I have time to put her on Jacks. Any thoughts? Thanks

[Edward J.]

Re: Carbs kicking my !@#$%

John,It sounds like your normal curb idle in park is a bit high, generally idling in park should it not be around 700/750 and then when dropped into drives around 650, unless your car will not idle at that RPM .Then maybe you do have a problem such as a vaccum leak or lean idle mixture.

Note: The difference in the RPM'S from park to drive is normal, it should drop about 200 rpm when the transmisson puts a load on the engine from the transmisson torque convertor.

[Duke W.]

Re: Carbs kicking my !@#$%

Corvette engine idle speeds are specified in neutral for manual transmissions and DRIVE FOR AUTOMATIC TRANSMISSIONS.

If you look at the AMA specs you will see that the '67 L-68 should idle at 550 in Drive, and the idle speed/mixture adjustment procedure should be conducted in Drive. (Be sure to firmly set the parking brake and chock at least one wheel for safety!)

Idle problems with autos when the OE camshaft is replaced with an aftermarket camshaft with more overlap are common such as poor idle quality and a heavy shock when shifting from Park or Neutral to Drive or Reverse. OE Automatic transmissions with typical 1800-2000 RPM stall converters DO NOT WORK WELL with high overlap camshafts.

You can give us an clue whether you have the OE camshaft by measuring the idle vacuum idling in Drive at several different speeds and remember that idle vacuum without the corresponding idle speed is meaningless because idle vacuum will increase with idle speed, whether it's a manual measured in Neutral or an auto measured in Drive. So always specify the pair, transmission type and whether the vacuum is measured in Neutral for manuals or Drive for autos.

Duke

[John M.]

Re: Carbs kicking my !@#$%

Thanks, I'll be under the hood all weekend trying to figure this out. I'm not sure if the cam was change or not, the car had been in a 35 year restoration. The owner passed away I have most of his receipts however the ink has disappeared on most of them. The car is running strong I just need to get a handle on this tranny before I break something.