Somewhere I read or heard about an adjustment on a standard 65 /6 carb in which you went for the maximum vacuum reading. I recall actually doing it once a long time ago, but can neither recall the details nor find reference to the procedure anywhere. It seems almost like it was idle mixture, but there should be no or low vacuum at idle, right?

Anybody know what I'm talking about?

Thanks

Actually you should have 17-21" of vacuum at idle. You can adjust initial advance and air idle adjustment with a vacuum gauge.

sb

Sure, if you had no other option you could 'ballpark' using a vacuum gauge but it shouldn't replace using a good timing light and tach meter. A vacuum gauge is a diagnostic tool to either comfirm proper engine vacuum or troubleshoot problems. Once you start tweaking both the timing and mixture using only a vac gauge, you could get even further off mark if you don't know what your doing.

At idle is when you have the most vacuum. You just have to find the right port to use. One that draws from below the throttle blades. Depending on rpms your vacuum will vary a pound or two.

Example: When mine is idling at 650 rpm with a one barrel I see 18" of vacuum. In gear it drops down to 16.5" at 550 rpms.

On timing you can advance it to the highest vacuum reading and then back it off a little. That is what you may have heard or remembered. But it really helps to have a timing light. My 74 was designed to run at zero degrees initial advance. Not fun nor very good mileage. After the rebuild and taking off most of the pollution control, I really like to run it a 16 degrees. 10 0r 12 degrees initial is real steady. 20 degrees when I feel crazy.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I vaguely recall helping a guy long ago time an Austin-Healy (I think--or some other very English roadster) that had NO timing marks at all. The drill was to advance the timing by vacuum, and then road test it. The manual actually specified to advance the timing until you pinged under heavy load, and then back off slightly until the ping disappeared. I never thought about it until now, but that is probably "perfect" timing for a given engine.

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Slanted D150

Yes, with a given curve of the distributor and vacuum can.

With a MOPAR you can adjust the vacuum pod and run a little more initial advance and still not have it ping, (by adjusting the pod with a 3/32 allen). Also by recurving the distributor, changing the springs you can eliminate ping.

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Aggressive Ted

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74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Thanks everybody. Turns out I had the right general idea.

No, I've never even heard of setting ignition timing on vacuum. I've always used a timing light for that.

The thing I had forgot was where to get the vacuum. Obviously the line to the distributor is useless, and the only port I have in the bottom of the carb is for the PCV line. What I forgot is that I had jury rigged a connection between that and the vacuum guage.

So between that, the vacuum guage and the tach I got it set up as I wanted it. Now I'll redo the valve settings and see if I can get a decent mileage out of this beast again.

Thanks again

"T" off the choke pull-off, that is where my gage is hooked up to.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG