Dancing Vacuum Needle
Thread Starter
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Moderator
Joined: Dec 2007
Posts: 7,987
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From: Boise, Idaho
Dancing Vacuum Needle
Hi all,
My engine hasn't had the greatest engine vacuum since I put the new head, valves, rocker arms, etc. in. It's always had an odd oscillating sound to the engine too.
After I finally fixed the lifter tick this weekend with some new lifters, I noticed the vacuum was really acting up. I'm not quite sure how to diagnose this, but I'm thinking a stuck valve of some sort.
Here's some videos:
Idling at 1000 RPMs. You can see how it "unsticks" itself, and then sticks from time to time. I also do a few revs at the end.
YouTube - MOV03E
Idling at 700 RPMs.
YouTube - MOV040
The tailpipe.
YouTube - MOV03C
Thoughts?
-
My engine hasn't had the greatest engine vacuum since I put the new head, valves, rocker arms, etc. in. It's always had an odd oscillating sound to the engine too.
After I finally fixed the lifter tick this weekend with some new lifters, I noticed the vacuum was really acting up. I'm not quite sure how to diagnose this, but I'm thinking a stuck valve of some sort.
Here's some videos:
Idling at 1000 RPMs. You can see how it "unsticks" itself, and then sticks from time to time. I also do a few revs at the end.
YouTube - MOV03E
Idling at 700 RPMs.
YouTube - MOV040
The tailpipe.
YouTube - MOV03C
Thoughts?
-
Thread Starter
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Moderator
Joined: Dec 2007
Posts: 7,987
Likes: 104
From: Boise, Idaho
Hey guys, thanks for the replies.
No, I haven't replaced the gasket yet. It's oddly on back order, so it's taking its time. I just thought this was too weird of behavior to be associated with just that.
No, I haven't replaced the gasket yet. It's oddly on back order, so it's taking its time. I just thought this was too weird of behavior to be associated with just that.
Post Fiend
Joined: Dec 2007
Posts: 8,521
Likes: 16
From: Lost
The MrG 260. like all "header" gaskets, start out fairly soft to conform to the surfaces, but after getting heated up, they start to harden. Once they have hardened from even 1 heat cycle, they can be nearly impossible to get a good seal on.
Just one of the many reasons I don't agree with the recommendation of using this gasket. Exhaust leaks aren't that big of a deal. Intake leaks are.
Just one of the many reasons I don't agree with the recommendation of using this gasket. Exhaust leaks aren't that big of a deal. Intake leaks are.
Thread Starter
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Moderator
Joined: Dec 2007
Posts: 7,987
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From: Boise, Idaho
I didn't know that about the MG 260. I like how well it seals, but it's a bummer it's a one time deal. A lot better than the Clifford though. I had to use a chisel and wire wheel to get that thing off.
I'll try a different PCV valve, and see how it responds once the gasket shows up.
I'd just never seen an intake leak do this before (and I've had my fair share of them!) so I wanted to be sure it wasn't something more drastic.
I'll try a different PCV valve, and see how it responds once the gasket shows up.
I'd just never seen an intake leak do this before (and I've had my fair share of them!) so I wanted to be sure it wasn't something more drastic.
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Elder User
Joined: Oct 2008
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The way the vacuum seems to self correct and how the exhaust just gives a random pop now and then seems more ignition to me. I would look at dirty cap/rotor terminals, dirty advance weights, maybe even a small partial bind of the distributor shaft. Maybe try new wires even, I suppose it's possible the old ignition is too tired to keep up with the air charge of the new head.
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Thread Starter
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Moderator
Joined: Dec 2007
Posts: 7,987
Likes: 104
From: Boise, Idaho
That makes sense, I'll have to see if something in the ignition is messed up. However, almost the entire ignition is less than a year old.
Come to think of it...though.... I did have the cap of the distributor the other day when I got hit with rain.
Come to think of it...though.... I did have the cap of the distributor the other day when I got hit with rain.
Elder User
Joined: Dec 2003
Posts: 660
Likes: 3
From: Northern California
Hey AB,
I had the bouncing needle syndrome and got it figured out.
My situation was:
I'm running a MSD Blaster Ignition, coil, and wires.
I set my plug gap to .055 as recommended as the "perfect" setting.
I hooked up my vacuum guage and the needle was bouncing/vibrating like in your video.
I re-gapped my plugs to .060 and the vacuum needle smoothed right out.
My random "pop" also disappeared.
Long story short, I'd be looking at your ignition system.
Hope this helps.
Bob
I had the bouncing needle syndrome and got it figured out.
My situation was:
I'm running a MSD Blaster Ignition, coil, and wires.
I set my plug gap to .055 as recommended as the "perfect" setting.
I hooked up my vacuum guage and the needle was bouncing/vibrating like in your video.
I re-gapped my plugs to .060 and the vacuum needle smoothed right out.
My random "pop" also disappeared.
Long story short, I'd be looking at your ignition system.
Hope this helps.
Bob
