ben442

Is there a specific number of turns out for these screws on this carb Number7041253 RE?

I started the car and hooked up a vacuum gage but got no reading from the port that I connected to. There are 2 lines on the front of the carb, both on the front right. I connected to the line that was not blocked off.
Carb is on a 455 with manual transmission

ben442

Here is an image of the two lines, The top gave me no reading on the gage.

oldcutlass

You connected the gauge to the ported vacuum port. It needs to be on the manifold vacuum port. The bottom port with the screw in the hose should work. If its an automatic, look for the line that goes to the trans, you can use that one. Adjust the left and right screws the same amount of turns to reach the highest vacuum on the gauge and then turn them in a 1/4.

RetroRanger

I think the start point is 6 turns out

MDchanic

Technically, there is no starting point for idle mixture screws in 1971, because they were set at the factory and capped.

However, in 1970 the recommendation is, in fact, for 6 turns, so that looks like the best place to start.

- Eric

oldcutlass

I don't remember them being blocked off in 71, I remember that starting in the mid to late 70's.

MDchanic

I know, I didn't either, but that's what the CSM says, right where it usually tells you how many turns to start at.

- Eric

joe_padavano

I believe the early 70s carbs had plastic limiter caps on the screws that only allowed a quarter turn or so adjustment. It wasn't until later that the lead plugs were used.

The screws with the tapered heads are designed to allow the plastic caps to snap over them.

Olds64

I thought the recommendation was 2.5 turns?

joe_padavano

That's what I thought as well. 2.5-3 turns out from fully seated as the starting point on a rebuild, then obviously adjusted as required with a vacuum gauge.

oldcutlass

Personally the starting point in turns is irrelevant, its the ending point that matters. The 2 idle a/f mixture screws should be equal in the same amount of turns when done.

joe_padavano

True, but it's easier to get to the end point if the engine starts more quickly.

oldcutlass

The biggest problem I've seen in peoples posts are the idle rpm is too high when they start and the a/f mixture screws do nothing when adjusted. The engine is pretty forgiving in starting whether very rich or lean. Anything from 2 to many turns out will get it to start. Its more important that the engine is warmed up, with the choke off and running with the idle rpm as close to what the book calls for when you adjust it. The carb needs to be adjusted last after dwell/timing is set.

joe_padavano

You mean as instructed in the CSM?

MDchanic

Which is exactly what I thought when I first read this question, and what I've always done, but I try hard no to give people inaccurate information, so I went to a couple of CSMs to double-check, and darned if it didn't say 6 turns.

Who knew?

- Eric

joe_padavano

Now you're going to make me check all my CSMs...

MDchanic

I only checked 1971 (the year of his carburetor), which said they were plugged, and then back one year to 1970, which has a table within the QuadraJet adjustment section, which gives the number of turns for each engine code.

I wonder about the other years, too.

- Eric

Octania

So, if adjusting the idle mixture screws makes no difference at all...?

joe_padavano

Vacuum leak or the throttle blades are open too far.

ben442

after sitting for a few days it's turns over a fair bit before firing up. It's not shooting any gas into the carb when I manually pump the throttle at the carb.
The bowls are empty I guess, Why? Do I need a rebuild?

Thanks
Ben