65 170 vacuum advance or not?

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wh23g3g

wh23g3g

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So I noticed something on my 73 Charger 400-4bbl when the mechanic came to my house to adjust timing and carb. He disconnected the vacuum advance and left it disconnected. It made a world of difference in how the car drives and performs. There was no hesitation and you could floor it without it stalling. He tuned the carb and adjusted the timing on my 65 170 but didn't leave the vacuum advance unhooked like on my Charger. Would it make any difference to disconnect it on my 170? It doesn't have power brakes or anything else. What does it do to change the way the engine performs? He checked my carb on the 65 170 and he said there's nothing wrong with it. He did say it would need some valve stem seals possibly because of the smoking. I think it may need a cylinder head rebuild. Because there's no telling how many years it sat before I got it.
 
If you disconnect the vacuum advance and driveability and performance improve, something is wrong and needs fixing. Without the vacuum advance working properly, you're throwing away money (reduced fuel economy), performance, and driveability. Leaving the vacuum advance disconnected is not a nifty advanced super-knowledgeable ninja mechanic technique, it's a hack—a word that applies both to the disconnection and the guy who did it. I would strongly suspect everything else this guy said and did.

That's if he actually disconnected the vacuum valve. Let's look a little deeper and figure out if that's what he really did. Your '73 (being a '73) was originally equipped with a device called an OSAC valve in the vacuum line between the carburetor and the distributor. It was a crude, primitive NOx emission control device that helped squeak the new '73s past their emissions type-approval tests so they could legally be offered for first sale. The OSAC valve delays vacuum to the distributor vacuum advance. It is notorious for causing poor driveability: mushy acceleration, hesitation, etc. When the OSAC valve is bypassed (vacuum hose re-routed directly from carburetor to distributor) then driveability improves considerably. So does fuel economy. If the OSAC valve is actually what this guy disconnected, then he did know what he was doing and he did you a favour, but there's no such valve on your '65.

So: What exactly did this guy disconnect and leave disconnected on your '73?
 
He's from a pretty well known racing family in the area so he's pretty good. He told me about that OSAC valve system and that's why he unhooked it. He said they never worked very well even when the cars were new. I had the osac and the vacuum bypass valve hooked up just like the factory service manual. Mine's a 400-4bbl so there is no egr plus I don't even have the factory intake on. It's a Weiand Action Plus with an Edelbrock 600. He set the timing and adjusted the carb. It made a world of difference and with that hose unplugged to the vacuum advance it actually would smoke the tires from a standstill. Before it would stall out. I just don't know if this Charger could be repaired enough to make driveable any time I want. But this Valiant is pretty simple and I feel even with the unknown miles on the Valiant that it seems already more reliable running than this Charger which has had everything gone through.
 
I'm not sure if you realize this or not, but the vacuum advance falls off when you stand on the go pedal, less vacuum the more throttle you give it.

First, take the hose off your carb that leads to the advance pod, and suck on it like a straw. Is there air coming through? If so, time for a new one! Be sure to check the multiplier on the arm and find one with the same or similar stamp on them. That number, multiplied by two, is the amount of advance it can administer. So make sure the math works out.

Vacuum Advance benefits are real.

Here is a primer:


http://www.camaros.net/forums/showthread.php?t=150344

After you've made sure your vacuum advance isn't a vacuum leak; My advice is to unplug the vacuum advance; make sure your base and total timing numbers are good.


Then plug the vacuum advance in and let it give you 8-16 degrees more timing, 48-52 TOTAL at 2500rpm or so for traditional heads like yours, CHECK ON THIS NUMBER for YOUR heads!

Adjustment is with a small allen head in the hole you plug the vacuum tube onto, 3/32" I believe. Righty is more, lefty is less.

Like DanTheMan said: There is NO loss of performance with a properly working vacuum advance, anyone who tells you otherwise doesn't know what the hell they are talking about.
 
Yeah I'm not 100% sure what all adjustments he did except, he did unplug the hose going to the vacuum advance, adjusted the timing, and mixture. It ran better than it did when I took it to a supposed Mopar specialist shop who spent two days with it. In fact it ran better than it ever has since I've had it. I'd ultimately like to get so reliable enough that I can get in take off and run to the store and come back home without stalling or overheating. After he did all that this past summer we took it our and drove it around for a good hour in the 85 degree weather and it had no problems. Right now it's been too cold to fool with the car even in the garage so I just try to start it, shift through the gears, and let it run for awhile until I can get it out and drive it. Over the winter I've added the suggested carb insulator gasket Edelbrock told me to get, re-routed the fuel line the best I could to get it away from the heat, and I changed out the fuel pump. Mine was putting out 7psi which Edelbrock tech told me was too high for their carbs. When I changed the fuel pump it did go down to 5.5-6psi on the gauge. Maybe it will be better now.
 
All he did was advance the initial timing. The 400 can easily stand around 20* initial because it has very low compression. Leaving the vacuum advance disconnected is a very dumb thing to do, especially on a street driven car.

It will drastically reduce part throttle response and the fuel mileage will suffer. The operation of the vacuum advance is to pull the timing up at cruise speed to help burn some of the extra fuel out of the cylinders and aid in pert throttle response.

He masked it being disconnected by pulling the extra timing in. Thing is, you can do both, as long as the vacuum advance can is plugged into a ported vacuum outlet.

You should check the initial timing where it is now. Then plug the vacuum can back into a ported vacuum source. It will run fine.

The fact that it is running better since he disconnected it is not because he disconnected it. It is because he pulled in a lot of extra initial timing.
 
I had all the vacuum lines hooked up according to the factory service manual eventhough I'm using a Edelbrock 600. Should I just run the vacuum hose from the vacuum advance to the carburetor and plug up the vacuum bypass valve in the water pump housing and the OSAC valve?
 
wh23g3g said:
I had all the vacuum lines hooked up according to the factory service manual eventhough I'm using a Edelbrock 600. Should I just run the vacuum hose from the vacuum advance to the carburetor and plug up the vacuum bypass valve in the water pump housing and the OSAC valve?
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Yes, I would eliminate the OSAC valve, per Dan's instruction. I cannot remember which port on the Edelbrock is ported. I THINK it is the one on the passenger's side in the front. That's where the distributor should be plugged in.
 
44932d1051772333-vacuum-line-timing-edelbrock-temp3.jpg
 
How would you tie in the vacuum bypass valve that sits in the water pump housing? Or would you plug it up too? I replaced it with a new one when I put the motor in the car. It ties in with the OSAC valve too. I read the description and operation of it in the factory service manual and it seems to make sense on paper. But is it really going to help anything or just plug it? It says it increases the idle if the temp gets too hot or something along those lines. I can't remember the exact description.
 
wh23g3g said:
He's from a pretty well known racing family in the area so he's pretty good. He told me about that OSAC valve system and that's why he unhooked it.
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OK, so he unhooked the OSAC valve. That's good.

with that hose unplugged to the vacuum advance it actually would smoke the tires from a standstill. Before it would stall out.
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Then something's wrong and needs fixing. The vacuum advance could have a blown diaphragm (vacuum leak), or it could be badly misadjusted.

But this Valiant is pretty simple and I feel even with the unknown miles on the Valiant that it seems already more reliable running than this Charger which has had everything gone through.
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Well, yeah, the Slant-6 Valiant's job is to get you there and back every single time. The 440 Charger's job is to turn tires into smoke and give you something to do every weekend.
 
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