The Stovebolt Site Forums The Shop Area Engine Shop 2nd vacuum advance unit fail in 16K miles,,,,

Not counting the original.
Noticed the engine was getting alittle harder to start, it lacked low speed pep and wasn't powering up inclines like it used to. Almost like I got ahold of bad gas.
Decided to check the timing out before shutdown and noticed the dist wasn't moving when goosing the throttle. Verified I had vacuum to the dist and my Mighty Vac verified the vacuum advance wasn't working. Like the title says this is the 2nd aftermarket replacement failure in 16K miles.
Just like the 6v heater blower switch I only seem to get a couple years use before they fail.
Dang things ain't cheap either, especially when you factor in shipping......
I'd almost just go on ahead and swap the engine out now but dang, I ain't ready to take it off line yet.

I know that I have run 60 year old vacuum advances in a couple of my old trucks without issue. Beyond me why the new ones go so quickly.
Hit the junkyards and like-minded buddies for a used one.

I can buy complete distributors with working vacuum advance units on Ebay at times, for less than the advance alone from some of the resto-ripoff places.
Jerry

Timely thread. I have reason to suspect my vac advance is faulty. I was just the other day looking at prices of the replacement units and they were 2x what I "guessed" they might be.

As I look for used or NOS replacements...did the vac advance EVER change during the 216/235 era? Some parts listings span 1937-1962. Others I see seem to be a more defined range of years.

I don't think it changed as far as basic size and application goes but the way the pivot arm connects to the diaphragm linkage does. You may have to drill out the pin and reuse it on the new replacement. Its an easy mod if needed.

I get the advance is bad and tested bad.........but...........the vacuum advance is really not a factor in cranking, at cranking speed and starting. It's vacuum supply is ported vacuum ........no ported vacuum with the throttle closed.

Too bad they can't be rebuilt. Not that complicated, just a rubber diaphragm in there right? Probably like thin bicycle inner tube now but shoe leather thick in the old days.

Good point. When cold I have to set the throttle open quite a bit to the point it runs alittle over 1k rpm once it starts. I do have the choke fully closed but move it to wide open choke once the engine starts.

With the bad vacuum advance I have to play with the choke some to keep it from dieing instead of my normal procedure of letting idle at wide open choke once it starts. In either case I let a cold engine fast idle (around 800-900 rpm for a minute or so before I drive it as it cuts down on stumbling.

I notice the performance suffering moreso than starting. Especially under load going up an incline or pulling out of a corner.

Look at how an automatic choke works- - - -it doesn't go wide open as soon as the engine starts. Keeping the choke closed partway for a minute or so will help the engine warm up better, and most carburetors have built-in fast idle linkage connected to the choke.
Jerry

Sometimes gas can get back into the vacuum chamber ruining the diaphragm. Put an upward loop in the tube where it comes out of the carb so gas can drain back.

I suspect your engine performance problem may be more likely due to the vacuum leak coming from hole in the advance diaphragm, rather than from the advance mechanism failing to do what it is designed to do.
Carl

At idle you shouldn't have vacuum pulling on the advance. Sounds like the timing is slightly slow to start with.

If the engine is backfiring that might be one reason the vacuum advances are dying so quickly.

But on start up and at idle there shouldn't be a vacuum advance. So double check the timing.

A lot of these engines didn't even run a vacuum advance in the heavier trucks. Just depended on the mechanical advance in the distributor.

Jerry, yeah I notice that but thought it was more to keep the mixture richer inorder to keep the engine from hesitating/stumbling until it warmed up.

Wrench, you may be right. My 72 ACVW's vacuum advance line has a trap in it to keep fuel from inadvertently making it's way to the dist. I may reproduce it on the 216.

Carl, Either that or the linkage has separated from the diaphram, hummmm....

Roy, that's right no vacuum at idle but there's vacuum at 1k rpm where I let it fast idle to warm up.

These units run anywhere from $35 to $75+ for an NOS.

Until the carb and intake heats up a little, only a fraction of the gas coming through the carb actually vaporizes before it gets to the cylinders, so keeping it a little rich for a minute or two is a good idea. Until the tree huggers started having a freakout over a few extra hydrocarbons, it was a lot simpler to make an engine run smooth during warmup. Just before everybody went to fuel injection, there was actually a federal law we had to comply with about how long an automatic choke could stay applied! I think it was 1 minute above 70 degrees F., and 2 minutes below that temp. That took a BUNCH of fancy adjusting, vacuum pull-offs, and electrically-heated choke coils!
Jerry