Hey guys, I have a 1974 dart 225 /6 it has a stumble when accelerating from a standstill, it will fall off and die sometimes when you try to accelerate to quickly. It does this mostly when cold. Also I got emmissions reciepts from the last owner, all the emissions are great but nox has climed a little over the past couple of years.

Anyhow I have checked through the vacuum of this car, I found a valve on the body of the air filter case. It is called an OSAC valve (Orfice Spark Advance control). The manual I have shows it connected in between the carb and the vacuum advance on the distributer. I am assuming this needs to be hooked back up. It is unhooked right now (the vacuum advance goes straight to the carb). The valve also says nox valve. It states in the manual that this helps control nox. I am wondering if this is only a california emmisions device or if it should be hooked up. Also could this unhooked valve be creating the stumble?

Thanks any help appreciated

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87 Chrysler Fifth Avenue 318
82 Dodge diplomat 318
74 Dodge dart swinger 225 /6
55 Chrysler windsor poly 301

I would do some checks, first make sure the vacuum advance pod is good. (holds vacuum)

Next, use a timing light and watch to see how the timing mark reacts to throttle opening. the mark should "jump" as the engine pulls-in the vacuum advance right off idle. (right when you crack the throttle)

Also use a vacuum gauge to see if the ported vacuum signel is strong off the carb's ported vacuum source. Sometimes if the carb is worn or the throttle blade is open too far, the ported vacuum is already pulled-in at idle, then retards as the throttle is opened, this make for a big stumble.

Let us know what you find-out.
DD

Isn't the OSAC valve just a delay device for vacuum advance?

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'66 Cuda 225/4spd
'66 Dart GT convertible 225/auto
'64 Dart GT 340/4spd

How about a bad accellerator pump?

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

The Ossac valve delays the vacuum signal coming from the carb. This means that when the throttle is opened, the vacuum signal take a pre-determined amount of time for the spark advance to build up at the distributor. It makes for a very lethargic feeling engine. It's purpose was to limit NOX, and it woked, but at great expnse in performnce and MPGs.

I have some sort of valve between the vacuum advance pod on distro and carb, it sits bolted to the edge of the head and has two wires coming out of it. On the side going towards the distro, there is a T on the output of said contraption. One side of the T goes to the distro, the other side is just open. Is this some later form of the OSAC valve? Can I remove it and just run the advance straight to ported vacuum source?