Carb help needed (please)

[Redmanf1]

I am a newbie here and I have a 72 GS 455 that I cannot get to idle correctly. I know it has a small cam but I do not have the info on it. The rest of the engine is stock except for the point replacement electronic ignition. The idle has to be set high enough that the ported vacuum has vacuum at idle. I had an extra 800 carb and drilled holes in the front butterfly’s to get to close enough for the port vacuum to work. I started with a 1/16 and ended up to ¼ to get the idle closed enough for the ported vacuum to close.
I am sure this is not the best way but I had to try something.
A recurring problem is when you put the car in drive @ even 950 rpm it wants to die after a couple of seconds.
I checked the timing and have set the mixture screws to peak vacuum.
I would really appreciate any and all help.

Thank you
Nelson

[77cruiser]

How much initial timing do you have? Sounds like you need more or you have a vacuum leak.

[Redmanf1]

It is set at 8 BTDC and I do not have a vacuum leak.

Thanks

[Marx3]

Sounds to me like a vuccumleak also, but if you say you dont have one... :-)

If the timing gets ported vacuum, try giving it manifold vacuum, that should stabilize the idle.

[Redmanf1]

The timing is set at 8 BTDC with a total at 32. The idle has to be set high enough to where the ported vacuum has vacuum. I did change some things which help stable the idle. The port that had the EGR valve vacuum hose attached to it has vacuum at idle. When I pulled the hose off the EGR valve closed, I plugged the carb port and the idle was much better. I also moved the dist adv vacuum hose to a full vacuum port. The car will now idle in gear with a drop in RPM of about 350. I did not have any other vacuum leak other than the EGR valve being open at idle when it was hooked up.
I know this is not correct way to get an idle but I could use some ideas for a better fix.

I did see a Q-jet carb with a custom mixture screw in the middle of the original ones (dead center), was this drilled for air adjustment? It was for a 454.

Thanks for all and any help

Nelson

[77cruiser]

The EGR can't be open @ idle or it will give you the symptoms you described. You might need some more initial with a cam.

[Cliff Ruggles]

The EGR was a BIG vacuum leak at idle.

If the ported vacuum is still being activated at idle speed, the carburetor needs more idle bypass air, and more idle fuel for the application.  Some fuel will be supplied by the main system if the throttle plates are open far enough to engage the ported vacuum slot in the baseplate......Cliff