Carburetor settings

[Gio_84]

Hi guys, I would need a little help from you.

 

I have rebuilt my carburetor with Cliff's kit and now I placed it on service.

The car is a Trans Am with a pretty stock L78 400 Pontiac.

I connected the  ignition advance with manifold vacuum, 22° at idle (750 rpm) and it has a little more than 15 inch of vacuum. The vacuum gauge needle is not very steady, it moves a little. It's not fluctuating, but it gos slowly a little up and down about a half inch.  what could be?

 

Then I setted the APT screw with the tip in procedure, at 2000 I choked the carburetor and the rpm reached 2250, I screwed down 1 turn and it reached 2500/2550 so I screwed it back about 1 and a half turn and it reached 2150/2170. is this correct?

 

Thanks a lot

[old cars]

Hi guys, I would need a little help from you.

 

I have rebuilt my carburetor with Cliff's kit and now I placed it on service.

The car is a Trans Am with a pretty stock L78 400 Pontiac.

I connected the  ignition advance with manifold vacuum, 22° at idle (750 rpm) and it has a little more than 15 inch of vacuum. The vacuum gauge needle is not very steady, it moves a little. It's not fluctuating, but it gos slowly a little up and down about a half inch.  what could be?

 What is half inch?

Then I setted the APT screw with the tip in procedure, at 2000 I choked the carburetor and the rpm reached 2250, I screwed down 1 turn and it reached 2500/2550 so I screwed it back about 1 and a half turn and it reached 2150/2170. is this correct?

 How many turns up from bottomed.What was it originally?
 Stock cam? Motor rebuild?

Thanks a lot

[Gio_84]

excuse me but it's not easy to explain.. what I mean is that the needle moves slowly in the range of an inch, from 15 to 14 and back

 

the screw is 3 and a half turns from the bottom, this is the second rebuild and unfortunately I don't know what it was originally.

 

the motor has been rebuild from a past owner but i don't know wich components he used.

I think the cam is stock

[Kenth]

I recommend to pull the idle tubes and drill .002" larger than present.
Also enlarge idle downchannel restrictions .002" to .005".
This will give better control of idle mixture needles for a strong stable idle in Drive (A/T).
Note: with A/T idle mixture needles has to be adjusted for best vacuum/rpm´s in Drive.

[Gio_84]

the idle tubes are already larger than the original, .029 to .035, Cliff sent them in the kit specifically for my application.

He also told me that .047of down channel restriction are enough.

 

you're right, I forget to set the idle screws in Drive!