Vacuum from ported at idle
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Mountain Pass
Joined: Dec 2020
Posts: 100
Likes: 6
From: Winston-Salem, NC
Last night I put initial at 12*, which is as far as I will go for idle. It increased rpm, so i could go to about 600rpm without ported vacuum. What still puzzles me is that when the initial at 6*, I got pinging.
Lead Driver
Joined: Oct 2018
Posts: 7,887
Likes: 2,369
If 22 isn't a correct reading that would be the most logical answer. but if it is then it's time to try something else and that would be setting it where it belongs. if it pings worse then you know something is wrong for sure.
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Mountain Pass
Joined: Dec 2020
Posts: 100
Likes: 6
From: Winston-Salem, NC
Just finished test driving it. Good news! Even though I increased the timing by 6*, it pings less. I think allowing the ported vacuum to remain dormant at idle, even if it comes in with just a hair of throttle, made it come in at the right time. Now that I know that it doesnt ping any worse, I will probably increase the initial by 2* more. As for the timing coming in late or not enough, I honestly could care less. Im not going to race it or anything, just something cool to drive in high school.
Thank you guys so much! Even if you didn’t directly help, you guys gave me ideas and much more knowledge!
Thank you guys so much! Even if you didn’t directly help, you guys gave me ideas and much more knowledge!
Tuned
Joined: Jan 2019
Posts: 364
Likes: 91
You might try manifold vacuum instead of ported. With the advance unhooked,set the initial,hook it back up and adjust idle speed. Test drive. If no ping,advance timing till it does and back it off till it quits. Reset idle..Lots of other factors involved but don't overthink it. Worth a shot...
Tuned
Joined: Jan 2019
Posts: 364
Likes: 91
Not so. Under load at the,lets say,the 1500,3000 rpm range,vacuum is greatly reduced so timing is retarded accordingly,eliminating detonation....IF (like I mentioned) all the other factors involved are in the correct ball park. Cruise advance works as usual with manifold vacuum. I'm not necessarily a big fan of manifold vacuum.but sometimes when you have a bunch of stuff thrown together,it will really help clean things up.
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Lead Driver
Joined: Oct 2018
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Manifold vacuum does drop as the throttle plates open that's correct, so does ported. Once the throttle plate moves past the timed port they're essentially the same.
until the mechanical is fixed the vacuum setting is a crap shoot at best.
until the mechanical is fixed the vacuum setting is a crap shoot at best.
Thread Starter
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Mountain Pass
Joined: Dec 2020
Posts: 100
Likes: 6
From: Winston-Salem, NC
A slight problem I have discovered. It all still drives well and pings less, but sudden acceleration is now a problem. At normal cruise its fine but with a slight press if the gas to get up and go, around halfway down the pedal, it boggs down. However, if you push it farther to the floor, its fine.
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Mountain Pass
Joined: Dec 2020
Posts: 100
Likes: 6
From: Winston-Salem, NC
Just something I discovered. One of the mixture screws is way off than the other one. The way my pa showed me to adjust carbs is to start at the same, and adjust one independently to highest vacuum and go to the second screw, and go back in forth once or twice. The left mixture screw is more or less “normal” but the right side one is basically all the way lean, so much so that its difficult to turn the screw. Even if I back the right one off, and turn the left one in, vacuum goes to hell and the engine stumbles. Essentially highest vacuum is when the screws are drastically apart. Any idea what is going on and how to fix it? Could this be the golden key to the ported vacuum issue?
Thanks, Sam
Thanks, Sam
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