help me troubleshoot....

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Jul 29, 2012 | 08:08 AM

79 vette head

Thread Starter

Burning Brakes

Joined: Sep 2005

Posts: 1,198

Likes: 0

From: staten island new york

St. Jude Donor '10

help me troubleshoot....

i'll try and keep it short and sweet.
engine: rebuilt L-48 headers and a mild cam.
i had a holley 750 on the motor and was always adjusting and i had a hot re-start issue. (which i think was my battery) new battery installed.plus if i had the idle set a little high i would get pre ignition on shutdown. i was told to try an edelbrock so i went and got a 600cfm. car ran ok for awhile then started to act up. the car slams into gear and the rpms drop very low and wants to stall. my mechanic told me the carb was no good "send it back". i did. put the new one on. same thing.... timing was checked carb was adjusted and it still not running good. vac. advance was disconnected and is running a little better...

why is the car slamming into reverse and drive??? drive is not as bad as reverse.

why is the rpm dropping so low when put into gear???
i need some help.....

Jul 29, 2012 | 08:23 AM

wombvette

Le Mans Master

Joined: Jan 2000

Posts: 8,918

Likes: 27

From: New Hill NC

Too much cam for a low stall torque converter. Or vacuum advance wrong for the set up, causing it to fall out when rpm falls as it goes into gear.

Jul 29, 2012 | 11:38 AM

hdpete98

Pro

Joined: Feb 2002

Posts: 709

Likes: 10

From: Carlsbad CA

95% of carb problems are electrical (I just made the percentage up but you get my point). Hot start problems are usually the timing to far advanced. Make sure distributer is tightened down. They can move causing the timing to advance over time. This would explain car initially being fine and then problem arising over time.

Jul 29, 2012 | 09:31 PM

thiatt

Instructor

Joined: Oct 2008

Posts: 176

Likes: 1

The vac line to tranny is disconneted or leaking is my guess. Causes hard shift vac leaks cause stalls.

Jul 29, 2012 | 10:34 PM

bobs77vet

Race Director

Joined: Sep 2004

Posts: 11,874

Likes: 263

From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod

consider this......your vacuum cannister is not pulling in full vacuum because of the cam change. so your idle is incorrectly set high and then when you put it in gear the rpm drops down and the vacuum advance cutrs out dropping the rpm even lower.

lets test this....take a vacuum pump with a gauge and hook it up to the distributor and see when the vacuum advance pulls in....
then use a vacuum gauge and see what vacuum you are pulling at idle. your vacuum advance should pull in fully before you hit about 3/4 of your idle reading. Lars papers explain this and will give you the right cannister nunmbers so you can fix this.

Last edited by bobs77vet; Jul 29, 2012 at 10:39 PM.