Disconnect vacuum distributor engine dies

[Bob & Sue 110]

Yesterday I was going to time the engine disconnected the vacuum from the distributor plugged the vacuum port engine would just die had to set fast idle to 2000 rpm to keep it running. Hooked vacuum back up ran fine at idle with the cam I have idle is 1000-1100 rpm. Took it for a short ride ran like crap when I opened the secondaries it popped and sputtered. 

It was running a little rich is why I went through things again secondary float was to high, checked total timing at 3000 rpm 45 degrees don't know how that happened reduced total timing to 34 degrees. It still won't run if vacuum is disconnected from distributor.

Using Pertronix ignition all I can think of is the vacuum advance can might be bad. Waiting on some new gaskets for the carb I tore the float setting gasket now leaking fuel new ones won't be here till Sunday.

I'm lost any ideas?

[Max Power 74]

Are you using a ported source or a manifold source? Factory used ported sources, so if you pull the vacuum advance at idle and it dies, that means the vacuum leak you created is doing it, or your engine is requiring a level of advance at idle of the vacuum advance to stay running. The latter should be the case, at idle you should have no vacuum advance, so the timing shouldn't be killing it, and it is hard to imagine the small vacuum leak created any problems.

Will it stay running if you immediately plug the vacuum leak? Are you plugged into a port or manifold source of vacuum for advance? What is your base mechanical timing set at?

[Bob & Sue 110]

I'm using a ported vacuum source.

I disconnected the ported vacuum and put a cap on it, tried to start it it wouldn't stay running under 2000 rpm.

Hooked vacuum back up to distributor and it started and idled at 1000 rpm.

Base is set at 10*

[barnett468 418]

you have vacuum at your ported vacuum source . i can tell you how to fix this later if no one else does, but for now you can disconnect and plug the vacuum then set your timing to 12 degrees.

set the idle as low as possible then advance the distributor slightly (around 3 degrees) while it is idling . if the idle goes up noticeably and it still idles smoothly, leave it there and drive it.

if it still turns over easily when you immediately restart it then this is an acceptable setting for idle but it may still want a little more . if it turns over more slowly with the higher setting then you need a start timing retard system.

 

set your float level so it is just below the screw hole or near the bottom of the sight glass immediately after you turn the engine off.

 

 

 

[DocWok 30]

3 hours ago, barnett468 said:

if it still turns over easily when you immediately restart it then this is an acceptable setting for idle but it may still want a little more . if it turns over more slowly with the higher setting then you need a start timing retard system.

Ummm...no real need for the added cost / complexity of a start retard system.

If your engine combination requires the extra timing at idle to idle acceptably  a properly set up vacuum advance connected to direct manifold vacuum will do the same thing for free i.e. no extra added advance whilst cranking only adding advance once the engine has started.

If you have the original type ford vacuum advance canister with the screw off vacuum inlet they are easily adjustable via the spring (different rate springs will alter the opening rate), spacer (can make your own spacer to limit total vacuum advance) and also shims for fine tuning the spring rate and limiting total vacuum advance as well.

If it is the later model vacuum canister with the non removable inlet they can also be adjusted via a small allen key inserted through the vacuum inlet tube, also a couple of aftermarket manufactures offer adjustable vacuum canisters and mechanical advance springs kits.

It takes a bit of effort to do but there's lots of information out there on the internet on how to correctly set up a vacuum advance system for a street driven performance engine if your engine requires the extra timing to idle acceptably and you find that adding extra initial advance causes hard starting / cranking issues.

[mwye0627 44]

Very confusing that your base timing would be at 10° yet with advance all in it would be 45°

unless someone had done quite a bit of work to the advance mechanism...

I did have a case about 10 years ago working on a friends 1969 Mustang with a 351W.

He couldn't get it to start and run after his dad helped him "Tune" it.  

I went over there and advanced the timing by ear and got it running pretty well...

Then I put a timing light on it and it showed 60° advance @ 3000 RPM!!!

WHAT???

Then I remembered working on a 1968 Camaro a few years earlier with similar symptoms...

The Rubber isolator between the harmonic dampener hub and outer ring had dry rotted

and the outer ring had rotated several degrees out of position!!!

That's exactly what had happened to this particular Mustang.  If the timing was REALLY

that high, it likely wouldn't have started, it would have just bucked back against the starter..

P.S. That's why the NHRA and other Racing sanctioning bodies have required aftermarket

Harmonic Dampeners (SFI Spec 18.1) made to prevent the outer ring from blowing apart at

high rpms...

In any case it's pretty easy to check if your harmonic dampener is showing 0 degrees in the

correct position...

Make a piston stop from an old spark plug. Break the ceramic isolator out and place a 1/4" bolt through

and snug a nut up against the bottom of the spark plug thread with about 3/4" of the bolt protruding.

Screw this test plug in the #1 cylinder spark plug hole and slowly turn the engine over BY HAND

until the piston stops against test plug and mark the harmonic dampener at the 0° mark on the timing

pointer.   Then rotate the engine in the OPPOSITE direction by hand until the piston stops against

the test plug again.   Mark the dampener at the 0° mark on the pointer again.

Now mark the harmonic dampener exactly in they middle of the first two marks.   That will be the TRUE

0° position...   If it's not at the original 0° position as etched on the dampener,, then you have found your problem.

It is best to replace the harmonic dampener with a NEW one at this point.

Wishing you the best of luck in finding your problem!!!

[barnett468 418]

2 hours ago, DocWok said:

Ummm...no real need for the added cost / complexity of a start retard system.

If your engine combination requires the extra timing at idle to idle acceptably  a properly set up vacuum advance connected to direct manifold vacuum will do the same thing for free i.e. no extra added advance whilst cranking only adding advance once the engine has started.

If you have the original type ford vacuum advance canister with the screw off vacuum inlet they are easily adjustable via the spring (different rate springs will alter the opening rate), spacer (can make your own spacer to limit total vacuum advance) and also shims for fine tuning the spring rate and limiting total vacuum advance as well.

If it is the later model vacuum canister with the non removable inlet they can also be adjusted via a small allen key inserted through the vacuum inlet tube, also a couple of aftermarket manufactures offer adjustable vacuum canisters and mechanical advance springs kits.

It takes a bit of effort to do but there's lots of information out there on the internet on how to correctly set up a vacuum advance system for a street driven performance engine if your engine requires the extra timing to idle acceptably and you find that adding extra initial advance causes hard starting / cranking issues.

ummm...and i have explained to some people how to do this if they insisted, however, if the throttle is opened even moderately quickly like it often is under normal driving, there is a transitional period upon initial throttle tip in where the timing can actually retard for a moment if vacuum is used to advance the timing at idle, therefore, for this reason as well as a couple others, the proper way to do it is to use a timing retard device . any other method is less than optimal and less than ideal.

 

 

 

 

 

 

[DocWok 30]

3 hours ago, barnett468 said:

ummm...and i have explained to some people how to do this if they insisted, however, if the throttle is opened even moderately quickly like it often is under normal driving, there is a transitional period upon initial throttle tip in where the timing can actually retard for a moment if vacuum is used to advance the timing at idle, therefore, for this reason as well as a couple others, the proper way to do it is to use a timing retard device . any other method is less than optimal and less than ideal.

Ummm....isn't that exactly the proper way vacuum advance is supposed to operate?

Extra timing in addition to the initial or mechanical advance. As soon as you open the throttle "even moderately quickly" the vacuum drops away and the extra timing from the vacuum advance drops away......just like it's supposed to.

No need for an additional timing retard device, the vacuum advance canister serves the same purpose for free.

[barnett468 418]

24 minutes ago, DocWok said:

Ummm....isn't that exactly the proper way vacuum advance is supposed to operate?

Extra timing in addition to the initial or mechanical advance. As soon as you open the throttle "even moderately quickly" the vacuum drops away and the extra timing from the vacuum advance drops away......just like it's supposed to.

No need for an additional timing retard device, the vacuum advance canister serves the same purpose for free.

ummm...no, that is not how it is "supposed" to operate when the engine is idling which is one reason why the mfg's do not use that method.

If one is looking for a cheap option, they can simply put a toggle switch in the ignition wire then simply flip it on after the starter is turning the engine over.

 

 

 

[DocWok 30]

2 hours ago, barnett468 said:

ummm...no, that is not how it is "supposed" to operate when the engine is idling which is one reason why the mfg's do not use that method.

Nope, your wrong Barnett, that exactly how it meant to and does operate.

[barnett468 418]

1 hour ago, DocWok said:

Nope, your wrong Barnett, that exactly how it meant to and does operate.

lol, you obviously have no idea what you are talking about and you can post that vacuum advance paper that was purportedly written by an "engineer" which i and countless others have debunked several points on if you want and it still will not change the fact that for at least the last 50 years, the mfg's didn't use vacuum to advance ignition timing at idle.

Here's another fact for you . The zero timing mark on the damper on a 1969 Z28 is NOT at zero . It is in fact advanced several degrees so it appears that the timing is less than it actually is so it could idle but still have the timing appear to be set within government guidelines.

 

 

 

 

 

[Bob & Sue 110]

Thanks for all the replies,

After installing the new secondary float adjusting kit (remember to loosen screw before turning nut unless you want to rip a gasket and leak fuel) the secondary float was set way to high after raising the float till it was just below the sight glass I was able to get it to idle at 850 rpm with a Mac auto tach my Sunn tach turns out to be a couple hundred rpm at idle.

Set the base timing to 12* with vacuum disconnected no problems this time.

I must have set the secondary float high by mistake when it was idling rough with vacuum disconnected I could see raw fuel in the carb must be why it wouldn't idle under 2000 rpm.

Took it out for an hour test ride runs and starts great again.

I have it on manifold vacuum now instead of the ported carb port I'm going to leave it alone.  

[barnett468 418]

47 minutes ago, Bob & Sue said:

Thanks for all the replies,

After installing the new secondary float adjusting kit (remember to loosen screw before turning nut unless you want to rip a gasket and leak fuel) the secondary float was set way to high after raising the float till it was just below the sight glass I was able to get it to idle at 850 rpm with a Mac auto tach my Sunn tach turns out to be a couple hundred rpm at idle.

Set the base timing to 12* with vacuum disconnected no problems this time.

I must have set the secondary float high by mistake when it was idling rough with vacuum disconnected I could see raw fuel in the carb must be why it wouldn't idle under 2000 rpm.

Took it out for an hour test ride runs and starts great again.

I have it on manifold vacuum now instead of the ported carb port I'm going to leave it alone.  

 

xlnt! I'm glad my suggestion to check the float level helped you.

 

Those gaskets have a tendency to stick so its possible that even if you did loosen the screw first, the nut may have had to be pried upward to loosen it which still may have torn the gasket . i spray WD-40 on them after I remove them which prevents them from sticking in the future.

 

As far as using manifold vacuum for the distributor goes, that really is a last resort and it can in fact cause it to have too much advance at idle which is one reason it should only be used as a last resort . Some canisters are adjustable but this still does not mean that one should use manifold vac for the distributor even if the canister is adjusted to limit the amount of advance they provide to an acceptable level . Also, if it idles fine without it, there is no real point in using manifold vac. 

Just a little more info in case you need it, you should always check the ported vacuum port at idle to see if it has vacuum as they sometimes do . If it does have very much vacuum, you can typically get it to have anywhere from less to virtually none at all if you advance the timing at idle, however, it is possible to have too much timing at idle, but if you use the method I described you will not . If there is still vacuum at the ported vacuum port after setting the initial timing to the optimum level, and the fuel mix screws have been properly adjusted and the idle is set as low as possible, you can reduce the amount of vacuum at that port by drilling a small hole in both front throttle plates . I have had to do this on many cars that had a large cam and it has often reduced the vacuum enough to make that port useable, however, I have also had some instances where there was still too much vacuum at that port to to use it and in these cases i used a different approach.

The vacuum canister has absolutely nothing to do with increasing horsepower, and your engine will feel like it runs exactly the same if you disconnect it, therefore, it is basically unnecessary and many engines did not even have one . One of the most well known of these engines is the 271 hi po which used a fully mechanical advance distributor, which means that it did not even have a vacuum cannister.

Here's a hi po distributor.

 

.

 

 

 

 

 

[DocWok 30]

Hey Bob and Sue,

Glad to hear you solved your problem and in this case connecting to manifold vacuum worked out for you !

[barnett468 418]

1 hour ago, DocWok said:

Hey Bob and Sue,

Glad to hear you solved your problem and in this case connecting to manifold vacuum worked out for you !

Actually that is not not what they said, however, they did say that lowering the float level fixed their problem.

 

 

 

 

[Bob & Sue 110]

Just to clear things up after I installed the new Holley 34-7 Needle and Seat Hardware Kit with gaskets.

1) disconnected coil wire, pumped secondaries by hand several times

2) turned float adjustment counterclockwise as far as it would go gently (raising float)

 3) turned engine over several times

3) turned float adjustment clockwise (lowering float)

4) shock side of car no fuel showing

5) repeated till there was fuel showing on lower part of sight glass

6) plugged coil wire in 

7) car started right up and ran smooth

8) checked timing & adjusted rpm 

9) adjusted low idle with vacuum gauge

10) rechecked rpm's 

11) plugged vacuum into manifold port

12) took it for a long drive stopped several times to see how it started, ran and started right up just like it should.

 

In the future I may go back to ported carb vacuum to see if there's any difference but not now.

Just started it didn't crank more than 2 seconds and fired up.

Again thanks for the replies.

[barnett468 418]

you should check the timing at idle with the vacuum disconnected and again with it connected . also, listen for an increase in rpms and a possible slightly erratic idle with it connected to ported vacuum then post all the results and i can tell you what is going on.

the vacuum can will not typically advance the timing while it is being cranked as there is rarely enough vacuum at this low of an rpm to operate the vac can.

 

 

[Max Power 74]

On 4/21/2017 at 9:52 PM, DocWok said:

Ummm....isn't that exactly the proper way vacuum advance is supposed to operate?

Extra timing in addition to the initial or mechanical advance. As soon as you open the throttle "even moderately quickly" the vacuum drops away and the extra timing from the vacuum advance drops away......just like it's supposed to.

No need for an additional timing retard device, the vacuum advance canister serves the same purpose for free.

When you open the throttle the manifold vacuum drops away, but if you are using a ported source, that's the first advance the dizzy sees. Ported should have zero vacuum at idle, so cracking the throttle suddenly provides some.

Running manifold vacuum to your dizzy is not really a good idea, and even worse if your dizzy is not curved for it. Even if you modified the curve to accommodate manifold vacuum, there are some issues with it. When tipping the throttle, with manifold you lose vacuum, and lose part throttle or tip in response. On an automatic car, when dropped into gear, you see a sudden decrease in RPM, therefore retarding the timing, often causing a stumble or a stall. This is especially prominent on cars with a fair amount of cam. Honestly, if you are running manifold vacuum to idle, you might just as well disconnect it entirely and re-curve to run nothing but mechanical.

The improved idle by connecting to manifold rather than port builds a false confidence. Yes, the idle improves (often masking other issues) but your tip in, part throttle and idle to throttle transitions get worse. Often much worse. And many people switching to manifold from a system designed for port fail to do any re-curving, making things worse.

[danno 128]

Ummm...  interesting discussions.  I learn a bit more when I read these discussions and try to make sense of it.  I need to verify my advance as well, but that is a different story for a different day.

[SWPruett 83]

It is interesting to note that MSD specifies ported vacuum on all of their vacuum advance distributors.  A really snotty cam will virtually demand ported vacuum in order to idle properly as there is no vacuum fluctuation jacking the timing all around as manifold vacuum would dictate in such an application.  Food for (further) thought.

[Max Power 74]

14 hours ago, SWPruett said:

It is interesting to note that MSD specifies ported vacuum on all of their vacuum advance distributors.  A really snotty cam will virtually demand ported vacuum in order to idle properly as there is no vacuum fluctuation jacking the timing all around as manifold vacuum would dictate in such an application.  Food for (further) thought.

Ironically many turn up the idle for said cams, exposing the transfer slots, suddenly providing vacuum to the ported source. Proper way to do it is through the secondary side.

[SWPruett 83]

39 minutes ago, Max Power said:

Ironically many turn up the idle for said cams, exposing the transfer slots, suddenly providing vacuum to the ported source. Proper way to do it is through the secondary side.

Yep!  I've seen it a thousand times!  Cracking the secondaries a bit at idle on a "cammy" engine can do wonders for returning idle control to the primary side AND cleaning up the ported vac signal.  Can't count how many times.......

[Max Power 74]

You see so many carbs at swap meets with holes drilled in the secondary butterflies, even on carbs that have the provision to crack the secondaries. Kinda crazy. I will say though, it would be nice if Holly made that screw easier to adjust. Having to remove the carb and guess at a setting for every time you make an adjustment is pretty brutal.

[SWPruett 83]

6 hours ago, Max Power said:

You see so many carbs at swap meets with holes drilled in the secondary butterflies, even on carbs that have the provision to crack the secondaries. Kinda crazy. I will say though, it would be nice if Holly made that screw easier to adjust. Having to remove the carb and guess at a setting for every time you make an adjustment is pretty brutal.

I have always pulled the Holley screw on the secondaries and replaced it with an Allen set screw with the socket end to the top.  Then all I do is manually open the secondaries and adjust without taking the carb off.  Never understood the bottom adjustment.

[Max Power 74]

On 4/25/2017 at 6:24 PM, SWPruett said:

I have always pulled the Holley screw on the secondaries and replaced it with an Allen set screw with the socket end to the top.  Then all I do is manually open the secondaries and adjust without taking the carb off.  Never understood the bottom adjustment.

Can you show me a picture of that?