Vacuum gauge question

[Joe Flanagan]

I just attached a vacuum gauge to the wiper port on the intake manifold of my engine. It flutters rapidly between 12 and 19. I am using the gauge off my hand pump vacuum tester because I haven't been able to find one that will thread directly into the port. I've got it connected to the port via a series of vacuum lines and adaptors that came with my vacuum pump, a bit jerry rigged but it appears that everything is tight and there are no leaks. I've tried carb spray and propane to see if there are any leaks around the carburetor and where the intake manifold bolts to the block but it doesn't look like there are any. I have a timing light but I don't know if it will work on a 6 volt system. I hooked it up just for the heck of it and while the strobe works, I can't see it on the pulley. I don't know if this is because I don't have the fenders on and there's too much light in the engine compartment or if it's because of voltage.

So: Any ideas on what's causing the fluttering needle and is this timing light OK to use?

Also, I forgot to mention that I played with the idle mixture screw to try and steady the needle and it has no effect.

[1942cowdodge]

Sounds to me that you should buy a real gage that shows if your timming is on or what? I have a couple of old ones and they work great! But they have printed on them at certain degrees what is going on inside the engine. I use it on my 87 Dodge and it works great.

[claybill]

joe....on the instruction sheet of the hand pump there is explanation for various needle responses....fluttering is one of them..check it out. or i will look this evening on mine. if i can find it.

bill

[greg g]

http://www.secondchancegarage.com/public/186.cfm

Scroll down and check scenarios 9 11 and 15

[Merle Coggins]

Pull your modern vehicle up to your car so that you can hook to it's 12v battery. Or use a jumper pack to power your timing light. The strobe is dim because it doesn't have enough voltage.

If your engine is like mine, the wiper port is at the back, near #5&6. You are probably seeing the pulses from those two cylinders rather than a smoother source at the carb. You'll probably need some kind of orifice in the hose to add some damping to your gauge. Orifices are commonly used on vaccum gauges used to sync multiple motorcycle carbs to reduce gauge pulse.

Merle

[38plymouth]

I use one of those to check vaccuum too. I found that with mine if I don't hold it tight in my hand the needle jumps around. It doesn't do it as much as yours so maybe thats not the problem but I thought I'd mention it. When I first tried it and had it laying on the cowl it jumped like crazy.

[Joe Flanagan]

First, on scenarios 9, 11, and 15 from the link Greg posted. They suggest weak valve springs, improperly adjusted idle mixture, and retarded ignition timing. My valve springs are new. Adjusting the idle mixture screw has no effect on the reading. And the condition for retarded ignition timing describes a slowly floating needle in a steady range. Mine is jumping like crazy between 12 and 19. Scenarios 5 and 6 sound more like it: burned or sticking valves. I sure hope that's not the case.

My vacuum wiper port is at the back of the block, near cylinders 5 and 6, so I'm hoping Merle is right and I'm just picking up pulsation from those two. The manual that came with my vacuum gauge by the way indicates sticking valves. Where have you guys gotten your gauges because I'm not entirely sure this jerry rigged system I've got going is giving me an accurate reading. Could I also attach it to the port for the vacuum line on the carburetor?

[Don Coatney]

A while back on a road trip I connected Greg G's vacuum gauge to my engine and it fluttered. My vacuum gauge shows a rock stedy reading. As has been mentioned by others in this thread, there must be some type of anti flutter device in my gauge.

I have said this many times on this forum but nobody has ever challanged me. I wish somebody would challange me on this. Connect your timing light to the coil wire as opposed to the #1 plug wire. By doing this the light will fire everytime the coil fires. Also when doing this you will get 2 hits everytime #1 fires as well as six hits per engine revoloution and all these hits brighten up the area so you can see the timing marks much better in the dimely lit area surrounding the harmonic balancer. If you dont believe me try it.

[greg g]

Joe I hate to say this but a sticky valve, Ie one that is not closing therefor not sealing, will allow vacuum to collapse on that cylinder, like wise a valve that is mis adjusted, will also not close and cause the same symptom. You did mention they you did a recent adjustment. Perhaps a revisit might be necessary.

[Jim Yergin]

Joe,

Maybe its time to take a trip to Harbor Freight in Woodbridge.

http://www.harborfreight.com/catalogsearch/result/?category=&q=vacuum+gauge

Jim Yergin

[Joe Flanagan]

Don,

Actually, I took up your challenge today. I read an old thread where you suggested doing this. I did it, and I got more light and faster light but still not enough to be able to see it on my damper. But I was fooling around with a 12 volt timing light.

Greg,

Unfortunately you may be right. First I'm going to see if my method of attaching the gauge is whacked. Probably going to get a proper gauge at Harbor Freight tomorrow (thanks, Jim, you read my mind). I will recheck the clearances on my valves. But as I recall, my feeler gauge slipped between them all. The only time you should be able to get the gauge in there is when the valve is closed, correct?

[DutchEdwin]

Joe, not all hopes lost. When I did my first check on the engine vacuum I used a normal vacuum meter from a hardware store. Had exactly the same as you, fast jumping needle and sometimes when I did hold the gauge in my hand the needle was a little more steady. A colleague gave me an old vacuum meter like Don showed. The needle was rock steady on this one. What's the difference? The gauge I used was hooked up with a "hard" rubber tube, the other one with a soft rubber tube. Giving it a better seal. So it turned out I had a leak at tube of the gauge. So before you take the engine apart, use a second gauge to test. Could be a simple thing like this.

Good luck

[Joe Flanagan]

That's what I'll do, Edwin. Check the simple things first. I would hate to tear into this thing. I'm almost at the point where I can put the hood and fenders on permanently. I'm keeping them off right now until I can sort all this stuff out.

[Merle Coggins]

I have said this many times on this forum but nobody has ever challanged me. I wish somebody would challange me on this. Connect your timing light to the coil wire as opposed to the #1 plug wire. By doing this the light will fire everytime the coil fires. Also when doing this you will get 2 hits everytime #1 fires as well as six hits per engine revoloution and all these hits brighten up the area so you can see the timing marks much better in the dimely lit area surrounding the harmonic balancer. If you dont believe me try it.

I have tried it. I found the mark would read a couple degrees difference between putting the clamp on #1 and on the coil wire. I also found that if I use the advance dial on my timing light while connected to the coil wire it wouldn't advance the mark like it does when connected to the plug wire. Not sure why it would matter but it does. I double checked everything and tried it again and got the same results. So I only clamp to #1 plug wire now.

Merle

[Don Coatney]

Don,

Actually, I took up your challenge today. I read an old thread where you suggested doing this. I did it, and I got more light and faster light but still not enough to be able to see it on my damper. But I was fooling around with a 12 volt timing light.

I have tried it. I found the mark would read a couple degrees difference between putting the clamp on #1 and on the coil wire. I also found that if I use the advance dial on my timing light while connected to the coil wire it wouldn't advance the mark like it does when connected to the plug wire. Not sure why it would matter but it does. I double checked everything and tried it again and got the same results. So I only clamp to #1 plug wire now.

Merle

Joe and Merle;

Thanks for trying! Intersting results Merle using the advance dial. Tell me more about how the advance dial works??? I do not have one on my device.

[Merle Coggins]

Advance dial... When checking your timing advance devices there aren't enough marks on the pulley to show when you're at 25 degrees, or there abouts. Turn the advance dial and it advances the pulse of the strobe so that it appears that the timing isn't as advanced. In other words you can read your "0" mark at the pointer even though your timing is much more advanced than it shows. The dial on the timing light shows esactly how much advance you have dialed in.

Merle

[Joe Flanagan]

Very interesting, Shel. You know, I even rolled the thing back into the garage where there were shadows in the hopes I could see something. At the moment I'm in a horizontal position and about to shut my eyes, so I won't be running out there to check the timing. I'm not that dedicated. We'll see what happens tomorrow with the right kind of vacuum gauge. Hopefully my sleep won't be haunted by images of trying to unstick a valve, or worse, having to remove a burnt one.

[Don Coatney]

Advance dial... When checking your timing advance devices there aren't enough marks on the pulley to show when you're at 25 degrees, or there abouts. Turn the advance dial and it advances the pulse of the strobe so that it appears that the timing isn't as advanced. In other words you can read your "0" mark at the pointer even though your timing is much more advanced than it shows. The dial on the timing light shows esactly how much advance you have dialed in.

Merle

Understood, thanks.

[Cpt.Fred]

joe, i have the same indication on my gauge: week springs, burnt stuff, sticky broken blah.

i didn't really want to read it all...

my needle wasn't jumping, though.

i'll try checking again since i adjusted the valves a third time yesterday morning and i think i'm good to go now.

hooking up a 12V sure helps, did the same here. that's how i found out my vac advance wasn't working.

i'm feeling with you, sure hope you get it all set up!

best wishes from over here!

greg: thanks for the link, good read!

[Joe Flanagan]

So it appears I just needed the right type of gauge. I went out and got one like Don pictured and my reading is a steady 18. Just a hair into the region that says, "Late ignition timing." I assume adjusting the distributor will correct this?

[DutchEdwin]

Joe, glad you solved it. Here it is impossible to find a new vacuum gauge you bought in a shop like napa. Just to few people mess around with the old engines, or the tools lasts to long.....

[Joe Flanagan]

So today I moved the distributor just a tiny bit toward the front of the car and I got the vacuum into the normal range, about 19 inches. When I accelerate though, it goes down to 15 and the engine stumbles. This happens at around 1500 rpms. From everything I've read, I should now check the small wire inside the distributor and make sure any step-up devices on the carb are working, is that correct?

When I rebuilt the distributor, I replaced that wire with a thicker one and I've always wondered if it was too stiff to allow the plate to move. I was able to move it pretty easily with my finger but whether the vacuum from the engine can do it is unknown. I know that the diameter of the original wire is very small.

Going to follow Shel's advice and check my timing once it gets dark. Should be a balmy 95 degrees by then.

[Jim Yergin]

Joe,

What I want to know is what else you bought when you were at Harbor Freight?

I always feel like a kid in a candy store when I am there. I never realize how many additional tools I "need" until I am in the store.

Jim Yergin

[Joe Flanagan]

Jim,

I wound up not going to Harbor Freight. I found a store near me that had one. I was not looking forward to driving down to Woodbridge, believe me.

[Jerry Roberts]

joe, i have the same indication on my gauge: week springs, burnt stuff, sticky broken blah.

i didn't really want to read it all...

my needle wasn't jumping, though.

i'll try checking again since i adjusted the valves a third time yesterday morning and i think i'm good to go now.

hooking up a 12V sure helps, did the same here. that's how i found out my vac advance wasn't working.

i'm feeling with you, sure hope you get it all set up!

best wishes from over here!

greg: thanks for the link, good read!

Capt Fred , If your vacuum advance isn't working , that means that the diaphram probably is torn , and that means that you probably have a vacuum leak through the diaphram .