Timing adjustment--vacuum gauge

[Joe Flanagan]

I have a slight stumble in my engine on acceleration. I have a vacuum gauge hooked up to the wiper port on the intake manifold and the needle is in the "normal" range (according to the gauge) but a little on the late side. I have about 19 inches of vacuum at idle. The needle moves a little up and down at idle and you can hear it in the engine. The diagnostic guide for the vacuum gauge that was posted here some time ago says this indicates late timing as well.

So tomorrow I'm going to adjust the timing using the vacuum gauge alone, trying for the highest reading I can get at idle as suggested on this site. My question is, is it possible to get it too far advanced this way? Should I cross check against my timing marks?

If you say yes to this it means I have to stop being such a cheap baxtard and stop borrowing my neighbor's timing light and go get one of my own.

[Martin53Cranbrook]

well i know with my car i can't trust the marking on the pulley and with as much as it wobbles i can't get a decent reading with a timing light anyway so if this vac-timing works out i am curious to try that instead.

[james49ply]

very easy, timming to far advanced, missfire at idle and at high rpm, more so on the high rpm, retarted timming, exhaust 'thumps' at the tailpipe, set the timming where the idle is smoothist and quiet at the pipe, it's called 'timming by ear'

[Don Coatney]

Years ago I read on this forum that one should set the timing for the highest vacuum reading. I did this and developed spark knock while ascending hills indicating way too much advance. Reverted back to the timing light and will stick with it.

Blueskies also was running with too much advance and this caused failure of a wrist pin bushing in his engine. I am now running between 0 and 2 degrees advance. I have no spark knock, a good slow idle, and plenty of power on the hills. If I advance my timing I may have more power on the hills but I dont need it and I dont want to run the risk of wrist pin failure. I am in this for the long haul now.

[greg g]

Last time I did mine with the vacuum gauge, I to had some under load spark knock. I backed it off (retarded) till the knock disappeared. When I rechecked with the gauge, I was at 19 inches (a bit low but expected with dual intake) my timing light shows about 4 degrees BTDC at idle. My idle is about 700 Rpm. Starts well, climbs and accelerates with enthusiam, and gives good fuel economy.

[Don Coatney]

Last time I did mine with the vacuum gauge, I to had some under load spark knock. I backed it off (retarded) till the knock disappeared. When I rechecked with the gauge, I was at 19 inches (a bit low but expected with dual intake) my timing light shows about 4 degrees BTDC at idle. My idle is about 700 Rpm. Starts well, climbs and accelerates with enthusiam, and gives good fuel economy.

Goes to show that not all engines are the same. I dont think there is a correct answer for all engines. Each one must be done to what makes it run the best or makes the owner happy.

[Joe Flanagan]

What Don mentions is the reason I fear getting too far advanced with my timing. I will be checking it with the timing light, then. I wish now that when I refurbished my pulley that I'd painted more than the TDC mark. I left all the others unpainted and can't see them when the timing light flashes. In the absence of the other hash marks, is there any way to estimate how many degrees off TDC you are?

[Joe Flanagan]

I just checked with the timing light and it looks like I am quite far advanced. The only mark I can see on my pulley is TDC and right now that's about an inch or so to the left of the pointer when the strobe flashes. The odd thing is, my vacuum gauge has me at about 19 inches of vacuum, on the border between "normal" and "late."

My instinct is to go with the timing light and see how things run. When I'm at 1 or 2 degrees before TDC, the mark should be just a hair to the left of the pointer, correct? Like about a sixteenth of an inch or so?

[martybose]

Two thoughts for you:

First, the initial timing is meant to be set with the vacuum line disconnected and plugged. Depending on a few other things, having the vacuum connected could make it advanced up to 10 degrees from the initial timing.

Second, the easiest ways to time it is to invest in a modern timing light that allows you to always use the TDC mark by dialling in the initial timing. The one I have is an Innova 3568 that I bought on eBay that allows me to set the advance at 4 degrees (or whatever) and use the TDC mark.

Marty

[Joe Flanagan]

Seems I've read here that the vacuum line should remain connected. If I were to disconnect it, would it be from the carb side and plug that end?

[Niel Hoback]

No need to disconnect the vaccuum line as there is no signal until the throttle is opened.

[Don Coatney]

First, the initial timing is meant to be set with the vacuum line disconnected and plugged. Marty

Marty;

That is true on your setup as you are using manifold vacuum to drive your vacuum advance. On a ported advance system there will be no vacuum unless the throttle is opened.

[Joe Flanagan]

Reset the timing today to what looks like about 1 or 2 degrees before TDC. Starts much better than it ever did. Also, the hesitation seems to be gone. It runs much smoother, too. The weird thing is as soon as I reset the timing, the engine developed a slow knocking sound at idle. I pulled each spark plug and there was no change in the sound. Opened the valve covers and it looks like that's where the noise is coming from. I inserted a feeler gauge in each of them and at several, the noise seemed to decrease. How the valve settings could change along with a timing adjustment, I don't know.

Anyway, I found a few that seemed too wide and closed them down some. A neighbor who was watching said the sound was much less. I buttoned everything up and ran the engine and it didn't sound any different. Shut the engine off. Started it up ten minutes later. The sound was gone. I have no doubt it will be back tomorrow.

[Tom Skinner]

Joe,

It sound like your Timed at "Static Timing" right now - which is fine if that what you want. But as the Bar Tender in The Movie "The Shining" once said to Jack Nicholson "If f I may be so bold as to suggest Sir, you might want to solve your problem " - you might try a Timing Light and reach Dynamic Timing.

That is to say get to the most economical setting, and then tweak the carburetor settings with a Vacumn Gauge afterwards. "In this way Sir you will have solved your problem".

Tom

[Joe Flanagan]

Well that's the first time I have ever heard anyone ANYWHERE quote the bartender from "The Shining." You're a good man, Tom.

I did set the timing with a timing light. It shows me to be a touch before TDC. The engine runs very nicely, accelerates smoothly, and since my last post, isn't making any noise. I will adjust idle speed and mixture tomorrow. Wish I had a tachometer for this car.

[Joe Flanagan]

very easy, timming to far advanced, missfire at idle and at high rpm, more so on the high rpm, retarted timming, exhaust 'thumps' at the tailpipe, set the timming where the idle is smoothist and quiet at the pipe, it's called 'timming by ear'

This diagnosis actually turned out to be correct. My timing was too far advanced and these symptoms describe exactly what was happening.