Vacuum Guage Readings
Thread Starter
Instructor
Joined: Feb 2023
Posts: 159
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From: Benicia, CA
Vacuum Guage Readings
I'm delving deeper into whatever engine someone put into my 73 base model. The block number says its a 350 from a 1978-79 C-20 pickup and has an older Edelbrock Carb and intake that were designed for economy and low-end torque and what are probably the original heads for the C-20 (I haven't pulled the valve covers yet to get the head numbers). It idles kind of rough, so maybe someone put a mild cam in it? Also trying to see what condition it's in.
I hooked up a vacuum gauge the other day to see what I get. See attached video. From videos I saw youtube I'm not sure if the needle is fluctuating too much or not. The first 5 seconds was at a little leaner setting on the carb and the last 5 seconds I added about 1/4 of turn richer. Both are with RPMs set about 750.
Also, the RPMs vary from 730 to 770 over the course of every 5-10 seconds. I monitored this using a dial-back timing light I bought from Amazon, it's not a cheapo one, but not a name-brand either. Should the RPMs vary that much?
I hooked up a vacuum gauge the other day to see what I get. See attached video. From videos I saw youtube I'm not sure if the needle is fluctuating too much or not. The first 5 seconds was at a little leaner setting on the carb and the last 5 seconds I added about 1/4 of turn richer. Both are with RPMs set about 750.
Also, the RPMs vary from 730 to 770 over the course of every 5-10 seconds. I monitored this using a dial-back timing light I bought from Amazon, it's not a cheapo one, but not a name-brand either. Should the RPMs vary that much?
Thread Starter
Instructor
Joined: Feb 2023
Posts: 159
Likes: 31
From: Benicia, CA
In case no one can view the video, the vacuum reads about 16.5 in/hg, which I believe is an acceptable reading, but it twitches about 0.75 to 1 in/hg constantly. That along with the RPM varying 40-50 revs every 5-10 seconds, has me wondering if something is amiss. Thoughts?
1967 Pedal Car Champion
Joined: Mar 2020
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From: US-PNW
Uploaded the vid to my YouTube channel for all to see. C3 73, if you'd rather I didn't do that, just let me know and I'll delete it.
(edit: For some reason, it's not playing within this thread window, but if you click on the YouTube logo in the bottom right of the video it'll open in a separate window.)
(edit: For some reason, it's not playing within this thread window, but if you click on the YouTube logo in the bottom right of the video it'll open in a separate window.)
Thread Starter
Instructor
Joined: Feb 2023
Posts: 159
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From: Benicia, CA
Uploaded the vid to my YouTube channel for all to see. C3 73, if you'd rather I didn't do that, just let me know and I'll delete it.
https://www.youtube.com/watch?v=OC4CSHkxJ8U
(edit: For some reason, it's not playing within this thread window, but if you click on the YouTube logo in the bottom right of the video it'll open in a separate window.)
https://www.youtube.com/watch?v=OC4CSHkxJ8U
(edit: For some reason, it's not playing within this thread window, but if you click on the YouTube logo in the bottom right of the video it'll open in a separate window.)
No problems on my end, it started playing when I clicked play.
Thread Starter
Instructor
Joined: Feb 2023
Posts: 159
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From: Benicia, CA
I found a diagram (similar to the one posted above) that made me wonder if it was was valve issue, too. Like I said I'm too new at all this to narrow it down.
Does the RPM issue seem like it could caused by a stretched timing chain?
Thread Starter
Instructor
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From: Benicia, CA
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From: Southern Cal Ca
St. Jude Donor '22
Calwildlife, did u get the video to work? Or are you basing your thoughts on my description?
I found a diagram (similar to the one posted above) that made me wonder if it was was valve issue, too. Like I said I'm too new at all this to narrow it down.
Does the RPM issue seem like it could caused by a stretched timing chain?
I found a diagram (similar to the one posted above) that made me wonder if it was was valve issue, too. Like I said I'm too new at all this to narrow it down.
Does the RPM issue seem like it could caused by a stretched timing chain?
when you richened you gained vacuum and started to flux less, vid was short.
could be some misfiring going on.
sorry, short vid and I can't state whats up.
something you wrote triggered my loose chain comment.
could be a base timing and carb adjustment problem.
what does vacuum do at 2k?
Thread Starter
Instructor
Joined: Feb 2023
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From: Benicia, CA
I watched.
when you richened you gained vacuum and started to flux less, vid was short.
could be some misfiring going on.
sorry, short vid and I can't state whats up.
something you wrote triggered my loose chain comment.
could be a base timing and carb adjustment problem.
what does vacuum do at 2k?
when you richened you gained vacuum and started to flux less, vid was short.
could be some misfiring going on.
sorry, short vid and I can't state whats up.
something you wrote triggered my loose chain comment.
could be a base timing and carb adjustment problem.
what does vacuum do at 2k?
I've wondered if there's a mis-fire happening too. Like I said I'm trying to figure this engine out.
There is a clanking noise coming from the front of the engine that I'm trying to pinpoint. I thought it could be the alternator, but could it be coming from the timing chain maybe?
Pro
Joined: Jun 2005
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From: USA
Sorry it was a short video, vithought I was limited to the 20mb limit until 67:72 posted it to YouTube for me. If it helps I could post a longer video to YouTube.
I've wondered if there's a mis-fire happening too. Like I said I'm trying to figure this engine out.
There is a clanking noise coming from the front of the engine that I'm trying to pinpoint. I thought it could be the alternator, but could it be coming from the timing chain maybe?
I've wondered if there's a mis-fire happening too. Like I said I'm trying to figure this engine out.
There is a clanking noise coming from the front of the engine that I'm trying to pinpoint. I thought it could be the alternator, but could it be coming from the timing chain maybe?
Team Owner
Joined: Jan 2007
Posts: 53,648
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From: Southern Cal Ca
St. Jude Donor '22
a new symptom, noise in front?
I guess I would start with time chain.
pull dist cap.
turn crank clock wise, note/mark rotor pos.
turn crank counter clock and make sure rotor moves instantly.
pulling plugs will help and a good look at them may show something.
vacuum, I am hazy on what your needle bounce may show.
cam sounds lopy, what does needle show at a higher rpm?
I guess I would start with time chain.
pull dist cap.
turn crank clock wise, note/mark rotor pos.
turn crank counter clock and make sure rotor moves instantly.
pulling plugs will help and a good look at them may show something.
vacuum, I am hazy on what your needle bounce may show.
cam sounds lopy, what does needle show at a higher rpm?