Pertronix Ignition and Timing

[Beemon]

I've been battling timing issues for a while. Since I started this project, I've been checking vacuum in line with the pump, which is wrong. I've since hooked up a gauge to the manifold, and I'm reading at 15 inches of vacuum of 5* BTDC. The idle is smooth, but the vacuum gauge keeps telling me I have late ignition and sometimes off the line I have a bit of hesitation. I had to advance the distributor almost 15* for 18 inches of vacuum and the car idle hunts now. There is definitely an increase in power and driveability at this new timing, but would prefer a steady RPM at idle. I was naive at the time I had a shop rebuild the distributor for me, so I didn't ask about springs and weights (admittedly this is the first car I've ever worked on this extensively and everything I touch is new to me), so I don't know if the curve is the same or not. Has anyone else had timing issues with the Pertronix module? I'm starting to think that this is also a possible problem.

 

Also, curious, but what grade of gas do most people use?

Edited January 18, 2016 by Beemon (see edit history)

[old-tank]

Stock specs of your distributor attached.

The way I set timing:  with engine barely ticking over (300 rpm) and vacuum advance disconnected, set or observe timing.  Increase rpm to 2000 rpm and you should see the timing advance increase.  Connect the vacuum advance and bring the rpm up and you should see additional increase.  Using my "calibrated eyeball" it should be similar to the specs.

I have never seen modified springs or curve in a stock 56 distributor.  The Pertronix will have no effect on the timing.

Check back with you findings.

Willie

[Smartin]

If timing is too far advanced at idle, it will sound "lopey" and run rough.  How much timing do you have at idle now?

[NTX5467]

From my own "lookings around" years ago, I discovered that the vacuum gauge is a diagnostic TOOL, not an absolute situation.  Look more at how the needle acts than what the descriptions by the vacuum levels claim to indicate.  PLUS, manifold vacuum will decrease with increased altitude above sea level.  AND camshaft timing events can affect it too!!

 

As you advance the base timing, at idle, it can also lean the mixture from what it was initially, effectively, so what you're seeing could be lean misfire if you don't readjust the idle mixture screws.

 

I suspect that all the shop you had do the distributor work did was to disassembly, clean, lubricate, and then put it all back together.  Same advance weight springs, same advance weights, etc.  Unless it was a "hot rod shop" AND you requested some advance curve modifications (which would have been an extra charge!), then things probably happened as I suspect.

 

Remember,too, back when almost every mechanic had a vacuum gauge, they didn't usually have any other test equipment that was more sophisticated.  Things like "dwell tachs" and "timing lights" were things the "big shops" had.  Otherwise, you used the "spark rattle on acceleration" method of setting timing.  But by the middle 1960s, almost every service station mechanic had a reasonably-decent timing light and dwell tach for doing tune-ups.  AND . . . If you were a regular customer and they had some slack time, they might check some of those things "for free".

 

For what you're doing, set things "to specs" and optimize the idle mixture and speed for the highest vacuum level.  Then maybe about 1/8th turn lean from that, for good measure and maybe a little less tailpipe emissions.  Make sure it goes into gear smoooothly with no lurching and then drives off smoooothly from there.  If you might want a "little something extra" and possibly compensate for some normal timing chain wear, you might try going to 7.5 degrees initial base timing from the factory 5 degrees, with the same idle speed.

 

SOME engines will increase their base idle speeds with more base timing, at idle.  Some will NOT make that much difference.  Has to do with combustion chamber design.  NO universal rule on that!

 

As Old-Tank asked . . . "Let us know"

 

NTX5467

Edited January 19, 2016 by NTX5467 (see edit history)

[Beemon]

I'm sorry I often forget this myself, but my uncle had the heads shaved in the 80s. I don't know by how much but if I recall correctly, this would increase the compression ratio? I think I remembered reading that high performance vehicles with higher compression ratios have lower vacuum at idle. Is that correct as well?

[Airy Cat]

I run premium 91 octane gasoline in all of my Buicks.  87 octane is crap.

[NTX5467]

In the case of doing a valve job, many machine shops will "surface" the cylinder head's head gasket surface.  Not a "hot rod trick" per se, but just insurance the surface is flat.  Unless some measurements are made, depending upon the type of "surfacer", how much is "cut" can be open to discussion.  Not enough increase in compression ratio to matter, typically.  But it does conjur-up ideas of greater power, though, provided THAT the same thickness of head gasket is used as what the engine originally had.  I suspect that low-speed intake manifold vacuum is more influenced by camshaft specs than compression ratio.  Did he put a "racin' type" camshaft in there?

 

BTW, when I was trying to tune with a vacuum gauge, I NEVER did get anything past about 17" of vacuum on the gauge I had.  No matter what.  At idle.  Yet all of the publications said that idle should be at least 18" Hg.  I either had a bad gauge, compared to others, or there was something else goin on.  Once you learn what things normally sound like, you can tell when the engine is running well.  It'll make "happy sounds"!

 

NTX5467

[Beemon]

Cam is stock, everything on the engine is original except for a 401 spring retainer. My engine only had 15 when I got it

I'll reset timing tomorrow after I get out of school and report back. The only other thing I can think of is a choked muffler, but the vacuum gauge days otherwise.

[MrEarl]

Quite some words of wisdom here so far! Clicking the follow button now. Once all is worked out would love to see a video and hear the "happy sounds" of which Willis speaks ;-)

[Ben Bruce aka First Born]

Quite some words of wisdom here so far! Clicking the follow button now. Once all is worked out would love to see a video and hear the "happy sounds" of which Willis speaks ;-)

 

 

  Where is this follow button??

 

  Ben

[MrEarl]

upper right hand corner just below the big ad banner

[Ben Bruce aka First Born]

upper right hand corner just below the big ad banner

 

 You are so smart!!    Thanks

[Beemon]

I have yet to advance the timing but I was curious. Old tank why do you generally set your timing to about 7 degrees? I read in another thread while I was doing research that you set all of your Buicks to 7 degrees and I was wondering what type of benefits you gain from doing this.

[Beemon]

Checking back in. Timing at 5*, at 16 inches of vacuum. On all 3 of my gauges, +/-.5*.

[old-tank]

I have yet to advance the timing but I was curious. Old tank why do you generally set your timing to about 7 degrees? I read in another thread while I was doing research that you set all of your Buicks to 7 degrees and I was wondering what type of benefits you gain from doing this.

After many miles, I found that setting gives the best combination of driveability , power and economy.  On my cars it is advanced to the point that it almost pings.

After checking my notes 16-17 in Hg is my vacuum at 7* btdc...you have plenty of vacuum for it to function.

When the 56 Buicks were new there were customer complaints of rough idle due to the aggressive cam profile (which is needed to compensate for the small valves with reduced flow)  When I was rebuilding one of my 322's a friend who builds performance engines (ford and chevy) came by and picked up the old cam.  He asked what race engine that came out of...it was the long duration that was obvious to him.

If your engine is original, you should be OK, but if someone have been in there before then all bets are off.

Willie

[avgwarhawk]

The 322 did have the hottest cam in the industry at this time.

[smithbrother]

My dad would take a 40's Buick out for test drive, he would stop often to set timing so that going up a slight hill, in high gear if and when he gave it light to moderate throttle, it would begin to ping, he felt it was right. 

 

Dale in Indy 

[NTX5467]

In general, the "hotness" of a camshaft can be relative to the size of the engine.  When I was considering a camshaft upgrade for my '77 305 Camaro, from the 2bbl carb and camshaft it came with, I devised a formula to consider engine cubic inches, cam duration at .050" lift, and valve sizes.  For this to really work well, there would have to be several "givens" (i.e., same manufacturer, same engine family, same general port flow in a stock engine).  The resulting "figure" would indicate which way some things would relate if a known "liked" cam's characteristics were desired in a different-sized motor in the same engine family.  One thing NOT considered was "lobe centerline", which can affect other various things as "intake manifold vacuum at idle".

 

Therefore, small valves need to remain open longer for the same power characteristics as larger valves, same engine size, shorter camshaft events.  Smaller valves are supposed to mean "greater port velocity" of the incoming air/fuel mixture, and with correct entry angles, an "active mixture" in the combustion chamber.rather than a "slow" mixture (as I term it).  Valve sizing is dictated by bore diameter, usually, with total allowable valve lift having other limiting factors.  The longer duration, for its time, was where the idle roughness probably came in, I suspect, as many cams of that era were VERY mild compared to modern grinds.

 

Also, if port flow, in general, might be less that it needed to be, then valve lift and duration could be extended to compensate some, especially on the exhaust side of things.  AND, in that same general time, there was a "Horsepower Race" going on, so those wilder cams and rougher idles meant "power" to some . . . AND sales to "performance oriented" buyers.

 

NTX5467  
 

[JamesBulldogMiller55Buick]

I run premium 91 octane gasoline in all of my Buicks.  87 octane is crap.

Right/, 

91 or higher in mine . 

or I get detonation.  

And, I've been running Pertronix for 16 years with no issues

Edited January 21, 2016 by JamesBulldogMiller55Buick (see edit history)

[Beemon]

I drove the car on the highway today, a good 30 miles one way, and I think I confirmed the choked muffler theory. While accelerating, my newly working vacuum gauge dropped to zero under a heavy hill climb. To my understanding, it isn't supposed to go to zero under load and the range is supposed to be more like 5 inches. If you followed my other, recent thread, you would see I just got my vacuum gauge and wipers working properly. Can't be more thankful as it started to downpour on the highway on the way back home! Definitely putting exhaust in the budget this year, though. I guess it had enough clearance to flow sufficiently at idle and low load situations, but not enough under acceleration.

[avgwarhawk]

I drove the car on the highway today, a good 30 miles one way, and I think I confirmed the choked muffler theory. While accelerating, my newly working vacuum gauge dropped to zero under a heavy hill climb. To my understanding, it isn't supposed to go to zero under load and the range is supposed to be more like 5 inches. If you followed my other, recent thread, you would see I just got my vacuum gauge and wipers working properly. Can't be more thankful as it started to downpour on the highway on the way back home! Definitely putting exhaust in the budget this year, though. I guess it had enough clearance to flow sufficiently at idle and low load situations, but not enough under acceleration.

 

 The load is the amount of pressure being applied to the engine by opening the throttle. When you open the throttle the 16-18" of vacuum that the engine is holding underneath the throttle blades tries to equalize with the -0- vacuum in the ambient air.   The two function fuel pump helps wipers under heavy load situations such as going up hill.  You lose vacuum and quite a bit. If the engine is operating under heavy load at wide throttle opening (such as from a stop or pulling the car up a hill) then engine speed is limited by the load and minimal vacuum will be created.

 

 

Are you reading the vacuum off the manifold or a port on the carb?

 

Test your muffler theory. Remove the muffler.  However, some engines require some back pressure to run properly.  I believe your readings are correct and the engine is functioning correctly under load.  

Edited January 21, 2016 by avgwarhawk (see edit history)

[NTX5467]

I believe that all mufflers will collect "particulate" in the "low flow" areas of the case, especially if the rpm levels remain lower for a good deal of the time.  I know that, even on my '77 Camaro (when it still had the factory cross-over muffler), that when I'd use WOT throttle after there had been none for quite a while, that it would "blow stuff" out of the rear pipes at the higher rpms and flow levels.  It'd clear out after a while in that mode.  On my '70 Dodge Monaco, whenever the secondaries would open, similar "stuff" would result in  two small clouds (dual exhausts) that I could see with a glance in  the rear view mirror.

 

Now, I'll concur on the 5" Hg at WOT as being a reasonable vacuum level.  When I was doing some "on road" vacuum level checking on our '69 Chevy pickup (350 4bbl with factory single exhaust), it would stay right at 5" Hg at WOT as the secondaries on the QJet would open.  When the throttle was decreased to a cruise level, it returned to about 17" Hg on the road.

 

For a vehicle of that age with a single exhaust system (I suspect), I wouldn't really condemn the muffler just yet.  Reason is that many of those older systems, especially the stock ones, were quite restrictive compared to modern mufflers and larger pipe sizes.  At that time, carbs were probably not over 450cfm for a 4bbl and probably about that for a 2bbl.  So an exhaust system with a 2" exhaust pipe (or smaller!) kind of worked in concert with the smaller carb sizing to limit total power production (although it was respectable for what it was).

 

When you put the car on an overhead lift and "tap" the muffler body, if it "thuds" then there's probably some accumulation in there (at least on the bottom).  If you hear "granular rattles", then that's rust in there.  If you hear a "rattle", that can be a loose baffle.  Those older-design mufflers were restrictive, by nature, considering how may turns the gas had to make to get out!  "Quiet" was restrictive . . . "loud" meant "power", generally . . . but it's not always that case with modern mufflers.

 

On your next drive, be concerned with the vacuum levels at various cruising speeds on level ground.  See how they compare as the speeds increases, up to the max legal speeds in your area.  If the muffler is clogged, you can find the degree of clogging as significantly decreased vacuum levels and greater throttle openings at the higher speed ranges (which might end up being past the local legal limit--proceed at your own risk).  If things look good at these normal cruise speeds, then I'd say just drive it more and see if it improves with mileage (NOT just short spurts, but longer runs of 30 minutes or so).  That additional "seat time" can also give you the opportunity to relax with the car and learn more about how it wants to do things and when it's "happy".  You can see how it responds to throttle input, (off-idle and otherwise) even small ones, too.  AND this can also give you more of a baseline knowledge situation as you might prepare for later upgrades.

 

NOW  . . . once you know how things feel and "when it's right", then you can decrease the use of test equipment (including your vacuum gauge) as you'll know "the feel" and can tweak that slightly for a little better "car happiness factor".  And THAT can increase the joy of vintage vehicle ownership!  Especially knowing that YOU made it that way!! 

 

Sometimes, people get so caught-up in setting everything "to spec" that they forget about manufacturing tolerances, if they ever knew of such things in the first place.  I think that a CAR AND DRIVER article (on a 1969 Camaro they built-up back then) that a Chevy 350 V-8 could have about a 20 horsepower variation (high to lower) on the engine dyno test stand and still "ship" to the assembly plant.  Every part of the engine has a certain tolerance in fit and assembly, except possibly for bolt torques.  When those tolerances "stack up", the exceptional engine can result . . . or the more mediocre one can result, just depending upon which way things went.  Keyways to locate harmonic balancers have even been known to be "out of tolerance" (which can affect ALL engine operation settings!), but that is somewhat rare.  THIS can be why "sound and feel" can be more important than "a setting to spec".  Certainly, specs have their place and generally work well (especially when the engines are new), but sometimes a little tweaking or "playing" can make things a little better (as Old-Tank's base ignition timing setting has indicated).

 

In the case of automatic choke thermostatic coils, they have been known to tighten with age, which would mean that they would need to be set "leaner" than spec to get the choke to open as soon as it should.  My own experiences have proven that out, but then I want the choke "off" as soon as it can be for better general performance and no loading-up during warm-up. 

 

Enjoy and keep us posted . . .

NTX5467

Edited January 22, 2016 by NTX5467 (see edit history)

[Mudbone]

I drove the car on the highway today, a good 30 miles one way, and I think I confirmed the choked muffler theory. While accelerating, my newly working vacuum gauge dropped to zero under a heavy hill climb. To my understanding, it isn't supposed to go to zero under load and the range is supposed to be more like 5 inches. If you followed my other, recent thread, you would see I just got my vacuum gauge and wipers working properly. Can't be more thankful as it started to downpour on the highway on the way back home! Definitely putting exhaust in the budget this year, though. I guess it had enough clearance to flow sufficiently at idle and low load situations, but not enough under acceleration.

I would disconnect the exhaust pipe and do the same test over to be sure. That way you will know. Mud

[avgwarhawk]

 

 

 

 

Sometimes, people get so caught-up in setting everything "to spec" that they forget about manufacturing tolerances, if they ever knew of such things in the first place. 

 

 

 

Enjoy and keep us posted . . .

NTX5467

 

In short, do not over analyze to the point of frustration.  More than likely adjustments will not meet ever spec in the book.   Many of us get to where we want with our engines by using dead reckoning.   In doing so it has served me well over the years.  Especially with carbureted and points ignition vehicles.  Modern day vehicles not so much.  The computer does it all by the numbers!   

 

 

As far as clogged mufflers, my years in the auto repair business I never replaced or had to replace a clogged muffler.    However, I have replace plenty of melted and clogged catalytic converters.  When one of these is clogged you will know it as you sputter down the road at 12 mph max.

Edited January 22, 2016 by avgwarhawk (see edit history)

[buick man]

Not too get off topic too much here but would like to mention I found that my nailhead seems to run much better when it is allowed to breathe adequately so we removed the air cleaner one day and as things go on a warm summer saturday one thing just led to another.  As shown below it is set up with just as little as 6 degrees advance and runs surprisingly well on pump gas corn-hol .  

 

 

 

[avgwarhawk]

Not too get off topic too much here but would like to mention I found that my nailhead seems to run much better when it is allowed to breathe adequately so we removed the air cleaner one day and as things go on a warm summer saturday one thing just led to another.  As shown below it is set up with just as little as 6 degrees advance and runs surprisingly well on pump gas corn-hol .  

 

Nail head blown.jpg

 

 

Passing everything but a gas station.....

[MrEarl]

Passing everything but a gas station.....

 but at the speed of sound no doubt (enter sonic boom sound bite here)

was considering this for a WasHappeninOnDaForum but has gotten a bit lengthy....

[60FlatTop]

Sometimes there is just a sort of magic that happens when the tuner is older than the car. Just a seat of the pants opinion, of course.

 

 

 

 

[NTX5467]

Passing everything but a gas station...

IF you can see it in time to stop!

[Beemon]

Wow 5 months later and I have an update... sorry for the rez but I thought this would be better than starting a new topic, in case someone was using the search feature.

 

I had a new exhaust system put in last Saturday and boy did it make a difference. My base idle was 600 before going in and after it raised it to 800 RPM. Before it would be a real hassle to have the car idle at 450 RPM but now it sits there just fine. Driveability is greatly increased and the vacuum gauge never drops to zero under load. I still can't raise idle vacuum above 15-16 inches Hg. Timing set at the 7 1/2* mark on the balancer, Dwell reads 29. I did find out that the vacuum pump had developed a leak and was sucking oil back into the intake, which wetted a few spark plugs and caused a very lean mixture with a nasty billow of blue smoke and an intermittent idle miss. This however did not affect vacuum readings at all.

 

When I started this thread, I was using my original carburetor. I'm duplicating effects with the second carburetor I rebuilt myself so I'm going to assume the engine likes the 15-16 inches Hg, which is a bit unsettling since everywhere seems to point to 18-21. But as NTX had said earlier, the vacuum gauge is more of a diagnostic tool than anything else. The hand on the gauge wavers ever so slightly between +/- .5 inches, but remains fairly steady. After changing spark plugs, there is a faint popping noise coming from the driver side exhaust. Aside from that, there is greater performance now vs the old plugs.

 

Just to be sure, I wanted to follow up. I'm hoping this is 'normal'. I've disconnected the power brakes, windshield wipers and hot air tube (fairly certain this vacuum is pulled from below throttle plate) and also stuck my finger over the starter switch vent and the vacuum raised from 15 to ~16. I checked the torque on the intake manifold to heads, carburetor base to intake and everything is within spec. Sprayed starting fluid and water around base of gaskets and obtained no increase in RPM. Sprayed the choke spring to choke assembly gasket, choke assembly to carb gasket, gasket bowl to gasket base gasket and no increase in RPM. I checked to make sure the line to the vacuum advance was pulling vacuum, capped it off and still no increase in vacuum. I haven't checked compression in the cylinders but I was bored .030 and the engine now has 2000 miles on it. I even tried ethanol free premium but noticed no difference to ethanol.

 

I'm ready to put the first carburetor back on the car for a rebuild test and move on to the dual carb setup I've been wanting to play with, but I want to make sure this sounds right before getting too far ahead.

[SpecialEducation]

On 1/21/2016 at 10:16 PM, buick man said:

Not too get off topic too much here but would like to mention I found that my nailhead seems to run much better when it is allowed to breathe adequately so we removed the air cleaner one day and as things go on a warm summer saturday one thing just led to another.  As shown below it is set up with just as little as 6 degrees advance and runs surprisingly well on pump gas corn-hol .  

 

 

 

 

"Corn-hol" burns cooler than real gas, so that's not too surprising.  I know guys who run stoopid amounts of boost but are set to run on E-85.  It takes a lot more E-85 to do the job, so they have giant injectors to make up for it.

That said, the soft parts of our fuel systems weren't designed for ethanol.  With E-10, we were putting a new diaphragm in the fuel pump every spring.  No alcohol, no problem.

The Century got the high compression engine already, and shaving the heads didn't help.  Altitude also makes a difference.  In Kansas, we have denser air than the mountains of Colorado, so we have 87/89/91 here where along I-25 you would find 85/87/89.  I wouldn't feed that thing anything less than pure gas in the highest rating typical for your area (I can find 105 here, but that's not typical so that doesn't count).

[Beemon]

I'm starting to think this is an ignition problem.  After checking the shop manual it said if issues cannot be resolved by adjusting carburetor screws and there are no leaks and ignition is advanced to specs then there is an issue with the ignition system. 

 

I pulled spark plugs to check and replace and they looked fine except the fact that the threads were somewhat wet. 

 

Before pulling the plugs, opening the throttle slowly there is a formation of black smoke the higher the rpms, but nothing at idle. 

 

If I put my foot into the throttle, it bogs but if I ease into it, the car runs fine. 

 

I'm not an expert but this tells me that there is too much fuel in the combustion chamber and it's flooding the engine a little. The low vacuum tells me that it's not capable of burning all the fuel despite carburetor adjusted for maximum vacuum with three different vacuum gauges. 

 

Accelerator pump is working fine. There isnt a clog in the idle circuits because both circuits die out the more lean I turn them in. The fact that the black smoke is present at higher rpms and unnoticeable at idle tells me to eliminate the idle circuits as the culprit. 

 

All ignition parts are from napa. Something is telling me the stock coil is not putting out enough juice. I was told to go to hotter plugs first since they're cheaper. 

 

Am I on the right track here? Am I safe to guess that the engine cannot burn fuel quick enough the more I dump in on quick acceleration but is capable of burning fuel at a marginal pace? Should I try eliminating the resistor first? 

 

[old-tank]

Let's start over since I am confused 

The title of this thread is: " Pertronix Ignition and Timing "

Do you still have the Pertronix?

What carb is on the car?

Brand and number on spark plug used now?

Can you supply a link to discussion on other threads where this was covered?

Willie

[Beemon]

2 hours ago, old-tank said:

Let's start over since I am confused 

The title of this thread is: " Pertronix Ignition and Timing "

Do you still have the Pertronix?

What carb is on the car?

Brand and number on spark plug used now?

Can you supply a link to discussion on other threads where this was covered?

Willie

 

Pertronix was removed and replaced with points. Dwell is at 29. Timing is set to the 7 1/2* mark.

 

Carburetor is a Rochester 4GC.

 

Spark plug is AC Delco R43S.

 

I've made a mistake and should have just started a new thread, but this is the thread where I discussed carburetor float levels and setting dwell.

[NTX5467]

On the ignition side of things . . . when you ease into the throttle, the "load" the ignition sees is not increased very much.  When you throttle into it, the "load" the ignition sees spikes from the prior level, until the load is stabilized.  If you had an ignition "scope", you could see this in real time, especially with the engine loaded against the transmission in "D" and the foot brake fully applied.

 

I presume the polarity of the ignition system is as it should be?

 

Check the voltage in the ignition system from the battery to the ignition switch, then back through the bulkhead connector to the coil and such.  Plus the generator output and battery condition, for good measure.  PLUS the battery terminals themselves . . . inside of the cable ends and the outer surface of the battery posts.

 

On the carburetor side of things, check the MAIN System air bleeds.  When any of the air bleeds become decreased from the spec size, it makes that particular system go "rich".  What you do with the idle screws is ONLY for the idle system.  You might need to get the service manual with a detailed illustration to find where these particular bleeds might be in the air horn or venture cluster.

 

We've already been through the float adjustment, so no additional comments, there.

 

DO check the air horn to main body gasket to see if the float bowl wall is sealing against the similar part of the air horn itself.  Look for gasket indentations and magnitude thereof.  Reason is that with time, AND the perceived necessity of torquin' on the air cleaner wing nut directly, the center part of the air horn can be pulled upward enough to a "non-seal" situation between the throttle bores and the float bowl . . . sometimes.  Some carbs are worse than others in this area.  When the rpm is increased and air flow increases, especially with the choke plate somewhat angled, raw fuel can be pulled over the float bowl wall into the throttle bores, causing a "mosquito fogging" situation from the exhaust pipe (especially when the choke is operating upon cold start-ups).

 

I presume the ignition components are all reasonably new and still in good condition?

 

Please keep us posted,

NTX5467

[Beemon]

I do not think it is the carburetor at this point because the first one behaved the same way as this one. 

 

Spark plug wires, cap and rotor are a year old. Points and condenser, coil and resistor were replaced this year when I took the pertronix out. Spark plugs replaced two days ago. Generator was rebuilt and tested last year, battery was bought last year and I had it tested last month. Distributer is wired to the negative terminal of the coil, power from switch to positive. 

 

Forgive me for my ignorance as I've just figured out the car was missing a beat, or had a misfire, which couldn't be heard until the new exhaust was put in. It's on the driver side tail pipe but it's subtle and didn't go away with spark plug replacement. I don't ever remember it misfiring with the pertronix, but then the only issue I had with the pertronix was the idle hunting and surging from the voltage drop of the voltage regulator. The pertronix used a hot coil, and now I'm using a napa oem coil. 

 

Everything seems to be working, I just have lower than normal vacuum and my old plugs were wet on the threads. I'll check voltage to the system later when I'm not at work. The hesitation off idle I've heard could be relaTed to ignition and a weak coil. 

 

[JohnD1956]

Just so you know, it's not just your car that does this.  I had my carb rebuilt two years ago and it's done it since.  The one thing I've noticed, and it may be totally unrelated, is that if I use one foot to operate the brake and gas pedal, the car does not stumble most of the time.  To explain, I have had this car for 40 years and formed a habit of using my left foot for the brake in order to feather the gas pedal if it began to run badly while in use. After all these years it's a hard habit to break.   Anyway, it appears that the few seconds between lifting my right foot from the brake and stepping on the gas, the engine does not stumble off the line nearly as much.  That means, of course, that it still does it on occasion. 

I am thinking this is a vacuum related issue.  And may be low vacuum at the vacuum advance.

BTW  Like you, when I saw my vacuum readings I was thinking my engine had some internal issues.  However, KAD36 sent me a copy of a service note from Buick engineers addressing the unsteady vacuum readings for the 55/56 engines. I cannot find that letter he sent me,  but in summary, a fluctuation in the vacuum gauge at idle is normal for these engines and was attributed to the aggressive cam that was factory installed. 

[old-tank]

Your ignition seems to be in order, but check the plug wires for continuity from the terminals inside the distributor to the plug terminal.  Don't bypass the resistor...the points will burn.  It is easy enough to check for a nice blue spark at a plug and if present that is enough fire the fuel.  Even a weak spark will work unless the gap is excessive and at high rpm.

The 4gc is the only carb that has beaten me... replaced with a WCFB.  The off idle stumble was just too aggravating.  I could lessen the stumble by turning in the idle screws until the rpm dropped (leaner).  The black smoke seems to be a different problem.  Look down (best to use a mirror) the carb while bringing the rpm up slowly.  You should not see any fuel since it will be running off the idle jets below the butterfly and then the jets just above the butterfly.  There should not be any fuel from the accelerator discharge or the nozzles.   Then see what happens when you snap the it open quickly.  There should be a healthy squirt from the accelerator pump discharge and then spray from the nozzles.  Report back.

[Beemon]

Accelerator pump is working as intended. 

 

I was really hoping it wasn't the carburetor. It's really hard especially in Seattle traffic to just get up and go when you need to. I've leaned it out a bit a couple days ago and like you said it's not as bad but the car still tends to bog under initial load.

 

I'm going to check spark color and continuity when I'm off work today but I did use my timing light to see if all 8 plugs were firing and they were so I don't think I have a continuity issue. I'll check the rotor cap for wear or arcing too. 

 

I guess I'll also check and see if I can find a wcfb carburetor,  too. I know of one for a 55 locally. 

 

[carbking]

If you are burning corn gas in Seattle: before giving up on the carb, pull the airhorn and the primary venturi cluster. Measure the diameter of the idle tubes. Drill them oversize 0.002 inch. Reassemble, readjust idle, and try an additional 2 degrees initial timing.

 

Jon.