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Car Chugs Along Not Smooth


likeold
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Took ownership of my 1938 Buick Special about 3 weeks ago and have been working on it pretty much every day since. Finally got it registered yesterday and took it out for its maiden run today. She start's right up and runs well, idles smoothly and has pretty good acceleration when you step on the gas once she warms up. Two or three times there was a backfire, I have not tuned into where yet. Also she is a little harder to start when hot. What I did notice is the car tends to chug along when you're giving it minimal gas, she does not give a smooth ride. It has new spark plugs, distributor cap, electronic ignition, new wires and carburetor has been rebuilt. I'm not sure how long the car was sitting and how old the gas was but it was pretty much empty and I filled it up with fresh regular gas today it also has a new fuel filter just before the carburetor that appears to be clean inside. I'm thinking of checking the timing and perhaps the vacuum advance, what do you think?

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Iikeold:

 Yes I would check the timing and the vacuum advance. As I found out with my 1937 Model 41 after its long hibernation mostly it needed more loving miles to make the engine happy. It can also run better with a bit more advance since the modern fuel is more volitile. Not necessarily better just more volitile. Octaine levels were much lower in 1938.

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If you swapped out to a Pertronix I have found the timing is usually off and will need an adjustment. It isn't much but enough. Did you drive it at all prior to the swap ? Some people like the swap others don't. I have had it in 6 of my cars for years without failure.  Everything from a 39 Chrysler to a 65 Fury and my 49 Road Master

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We had exactly the same once with our '39 at 30 mph on town streets.  Not working hard but a jerky ride.  OK under power.  The culprit was a leak where the carburettor fits onto the manifold.  Air was being sucked in.  A little tightening of the securing nuts might be all it needs, or you might need a new gasket as well.

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So I'm trying to understand how to time this car. Seems like there is the traditional way with a timing light then they talk about the octane selector adjustment. Are these really one in the same or is there actually two different adjustments on the distributor. When the octane selector is more on the high side is that advanced or retarded timing? I plan to try and use the light today with a 12 volt battery but want to understand this first. See where my octane selector is set now with the attached pic.

20211114_081244.jpg

Edited by likeold (see edit history)
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17 hours ago, likeold said:

Took ownership of my 1938 Buick Special about 3 weeks ago and have been working on it pretty much every day since.

 

Ha - replace "3 weeks" with "2 months" and you'd be talking about me!  I just went through a similar investigation on my '38 Century.  I had an intermittent exhaust backfire that seemed to occur only when letting-off the accelerator abruptly after cruising at a constant 45 ~ 55 mph -- BANG!  Coincident was what felt like a lean surge while running at that constant 45 ~ 55 mph.  I didn't notice the surge so much when cold, but seemed to appear after warmup.  I went so far as to 'hot-wire' the coil to the battery with a jumper to rule-out an ignition switch or wiring issue.  Eventually it did backfire with the jumper, so I kept looking.  I changed the condenser also with no change.

 

Prior to this I set the timing as specified in the shop manual.  Mine was set well advanced from the book to the point where the starter labored to start the car hot or cold.  With the timing set to spec, it starts right up hot or cold.  With the timing set (6* BTDC in my case) I loosened the setscrew on the Octane Selector and aligned it to the center of the scale.  I suggest you do as I did and drop the clutch inspection cover and roll the engine by hand until you find the timing marks on the flywheel.  I used some white paint to highlight the marks (UDC and 6* ADV) because the engraving is very light and nearly impossible to see with the timing light otherwise.

 

Last week I pulled the distributor in order to determine whether the centrifugal and/or vacuum advance were functioning properly.  I was suspicious of the vacuum advance because of the association of backfire to lifting my right foot.  It seemed that sudden change in engine vacuum was somehow related...  Anyway, with the distributor out I connected my hand vacuum pump to the vacuum advance and determined that the vacuum diaphragm would not hold vacuum.  The breaker plate moved, but immediately slipped back unless I kept pumping.  I ordered a rebuilt vacuum advance unit from Bob's Automobilia (https://bobsautomobilia.com/) as well as new internal primary and breaker plate ground wires.  With the distributor on the bench I removed the breaker plate and cleaned and lightly greased the centrifugal mechanism.  I re-installed the breaker plate, new wires, new condenser and points.  With the distributor back in the car, I reset the dwell and ignition timing (as before).  So far, I haven't experienced a backfire and it seems as though the constant speed surging is gone (or at least significantly reduced).  I've only driven 20 or so miles so far, but fingers are crossed.  My suggestion is to set your dwell, timing and check your vacuum advance diaphragm for a leak.

 

Keep us posted!

Edited by EmTee (see edit history)
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1 minute ago, likeold said:

no way to set the dwell as far as I know with electronic point/condenser

 

Ah, you're correct.  I forgot that you have Pertronix...

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So I'm still trying to figure out the correlation between the timing marks on the flywheel and the graduation marks on the octane sensor adjuster are these one in the same ? I haven't tried to turn the distributor yet or hooked up the timing light. Can you tell with the picture I attached does it look like this car  has advanced timing or retarded timing according to the graduations on the distributor? It appears to be pushed almost all the way to the high mark for high octane. Again would that suggest that the timing is advanced or retarded where it sits now?

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The Octane Selector is basically a way of allowing 'roadside' timing adjustments to be made without a timing light.  As I tried to explain above, once I had my timing set per the shop manual (6* BTDC in my case) I then 're-zeroed' (i.e., centered) my octane selector.  The octane selector is simply a graduated scale that allows one to see approximately how crankshaft timing changes as the distributor is rotated (advance or retard).  With timing set as specified, the octane selector should be set to the center of its scale.  This is done by loosening a setscrew on the distributor and moving the selector scale to the center of the scale.  If the car starts pinging due to bad gas (as could happen back in the late 30's) the octane selector could be used to retard the timing a couple of degrees (move toward LOW octane), using the octane selector scale, to eliminate the pinging.  Conversely, when filled with 'Ethyl' the timing could be advanced from the spec value a few degrees (move toward HIGH octane) to take advantage of performance from the higher octane fuel.  Rotating the distributor back to the center position should restore ignition timing to the nominal spec value.

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27 minutes ago, likeold said:

Can you tell with the picture I attached does it look like this car  has advanced timing or retarded timing according to the graduations on the distributor?

 

I would not trust what the Octane Selector scale says until you verify that setting the timing per spec (which I think is 4* BTDC for the 248) has the octane selector at the center of its scale.  There's a setscrew at the top of the octane selector readout that allows it to be reset to center.  If the vacuum advance housing is pointed toward the firewall and is parallel to the crankshaft the timing should be 'in the ballpark'.  Pointing the vacuum advance more toward the engine block advances the static timing.

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Okay I think I get it, first you should set the timing with a timing light to the factory spec. Then you can move the scale under the distributor to the center. At that point everything is factory set then if you want to do a quick side of the road retard or advance you can see on the scale under the distributor. I just tried to hook up my timing light and my timing light is dead, I think I'll just turn the distributor a little bit and see what happens until I get a new light.

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Absent an operational timing light, for a quick test you can try the "power tuning" of our youth:  With a warmed-up idling engine with a vacuum gauge attached to the wiper port, advance the distributor to maximum vacuum, then retard by 0.5 to 1 inch of mercury, retighten clamp.  This MAY require you to adjust the octane selector so that it is on full advance with the driving setting, and then retard it for starting (cold starts especially).

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If like me, you'll probably need to hook your light up to a separate 12V battery.  Since my boat is in storage now I just used my boat battery for the timing light.  Also note that timing check needs to be done at 400 RPM.  If faster than that, the reading will be skewed by the centrifugal advance.  Vacuum advance is not an issue at idle, as the vacuum port is above the throttle plate.

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1 minute ago, Grimy said:

This MAY require you to adjust the octane selector so that it is on full advance with the driving setting, and then retard it for starting (cold starts especially)

 

That certainly sounds like the way my car was originally set when I received it.  It was painfully reluctant to start when cold.  (Hot wasn't that much better...)  Mine is currently set per spec (6* BTDC) and it fires right up -- hot or cold.

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Well I couldn't wait for a timing light so I just retarded the timing and put it to the center of the octane selector and took it for a quick ride I have no idea what the timing set at but the car ran 100% better. I will get a new timing light and a tachometer and get into this more later but it makes me feel better that she's running sweet.

 

As far as the choke I don't think it's working at all I noticed when I had the air cleaner off the butterfly was completely open when I started it cold. I guess that's better than closed, she is  stored in a  heated barn so starting is not an issue takes a few minutes to warm up.

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22 minutes ago, likeold said:

As far as the choke I don't think it's working at all I noticed when I had the air cleaner off the butterfly was completely open when I started it cold.

 

Just like mine is for now.  Even here in NY I give it 2 or 3 pumps and it starts up.  Have to feather the throttle for a few seconds, then give it a fast idle via the throttle knob.  After a couple of minutes it's ready to drive...

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EmTee nailed it, but to further clarify: Set the octane selector to zero with the knob tightened down, then set the timing to factory spec by loosening the distributor clamp (NOT the octane selector knob). Use a light or whatever method you intend to use to set timing. In this manner, "0" on the octane selector will now represent the factory default timing. The octane selector scale will allow you to make minor adjustments for better or worse gas using the octane selector release knob, but when you put it back to zero on the octane selector scale you are back at the factory default setting.

 

Modern gas is higher octane than 1930s gas, and some cars like to run more advanced than they did back then. In that case, you would just set the octane selector to "0" as above, but use the timing spec the car runs best at to set the timing (instead of the factory default) when you set the timing with the distributor clamp. Then you can use the octane selector to advance or retard the timing. "0" represents whatever spec you used when you set the timing initially by loosening the distributor clamp.

 

8 hours ago, likeold said:

When the octane selector is more on the high side is that advanced or retarded timing?

 

I believe "high" represents "more advanced" and "low" represents "more retarded" If you want to check for sure, remove the distributor cap, crank the engine, and see which way the rotor turns. Turning the distributor housing in the opposite direction of rotor rotation always gives you more advance.

 

Edited by Bloo (see edit history)
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1 hour ago, Bloo said:

I believe "high" represents "more advanced" and "low" represents "more retarded"

 

Yes, that's correct.  The rotor turns CCW, so rotating the distributor housing CW advances the static timing.

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2 hours ago, Bloo said:

EmTee nailed it, but to further clarify: Set the octane selector to zero with the knob tightened down, then set the timing to factory spec by loosening the distributor clamp (NOT the octane selector knob). Use a light or whatever method you intend to use to set timing. In this manner, "0" on the octane selector will now represent the factory default timing. The octane selector scale will allow you to make minor adjustments for better or worse gas using the octane selector release knob, but when you put it back to zero on the octane selector scale you are back at the factory default setting.

 

Modern gas is higher octane than 1930s gas, and some cars like to run more advanced than they did back then. In that case, you would just set the octane selector to "0" as above, but use the timing spec the car runs best at to set the timing (instead of the factory default) when you set the timing with the distributor clamp. Then you can use the octane selector to advance or retard the timing. "0" represents whatever spec you used when you set the timing initially by loosening the distributor clamp.

 

 

I believe "high" represents "more advanced" and "low" represents "more retarded" If you want to check for sure, remove the distributor cap, crank the engine, and see which way the rotor turns. Turning the distributor housing in the opposite direction of rotor rotation always gives you more advance.

 

 

I'm sure you know better than me but I would think you would set the timing to factory spec first then the octane selector to zero, what am I missing here?

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They are two adjustments that do the same thing. If you set the octane selector afterward, you don't know where you are.

 

If you set the octane selector to zero first, and lock it down, then set the timing (with the other clamp), then you know that "0" represents the setting you made.

 

 

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I think that all Bloo is saying is that the center (reference position) of the octane selector is a relative value.  Normally, as I did, that reference point is the specified timing value.  I believe Bloo was saying that you are free to find the timing 'sweet spot' that your car likes (which could be a few degrees advanced from spec) and then set your octane selector reference/center position there.  Then, you'd be advancing/retarding the timing from that point.

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21 hours ago, Grimy said:

Absent an operational timing light, for a quick test you can try the "power tuning" of our youth:  With a warmed-up idling engine with a vacuum gauge attached to the wiper port, advance the distributor to maximum vacuum, then retard by 0.5 to 1 inch of mercury, retighten clamp.  This MAY require you to adjust the octane selector so that it is on full advance with the driving setting, and then retard it for starting (cold starts especially).

 

 

Wow.....great idea. I didn't realize when you were young that Mercury had been discovered and placed on the periodic table of elements. Hell, I thought you were using naphtha in your cars since gasoline wasn't invented yet.......who knew? 😎

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Greetings all,

I am a bit late to this thread, however the approach I take to timing my old cars has been very successful and was not mentioned above, therefore I offer the following recommendations based on my original experience with old Porsches, which are very sensitive to improper timing, overheating when retarded and detonation leading to piston failure when too advanced.

Setting the timing in this way, initially, is a bit of a hassle (but absolutely worth the effort).  You will need to get a stroboscopic timing light that allows you to set the advance at the timing light.    Also, my timing light is 12V, my Buick is 6V, so I need to bring a 12V power source close enough to the Buick to run the timing light.

  1. If the "octane" ruler is intact on your distributor, you have two adjustments.  One (fine) that allows you to adjust the distributor using the pointer, and one (gross) that allows you to move the entire distributor assembly relative to the position of the engine.    I like to set and lock the octane pointer at 0 using the "fine" adjustment before I use this timing technique, so that I know, exactly, what base timing setting is, and can ascertain how much I am altering that base setting when I "fine-tune" the distributor using the pointer.
  2. Set the light for 32-36 degrees advance.
  3. Connect light to 12V external power source, and inductive pick-up on #1 spark plug wire.
  4. Loosen the "gross" timing adjustment to allow the entire distributor assembly to move relative to the engine.
  5. With the engine running at cruising speed (fast enough that both the vacuum and mechanical advance mechanisms are no longer effecting the timing), turn the distributor such that the TDC mark on the flywheel appears in the timing window.  This sets your maximum overall advance to what you have specified on the timing light. 

This type of "total timing" is ideal because it compensates for all mechanical wear in the ignition system.  I live at high altitude, so I initially use 36 degrees, and rarely need to make any further adjustments.

Fine tuning the timing for your car and world:  Once you have set the timing, you can fine-tune the timing once you have the engine at operating temperature.  You want the timing as far advanced as possible without pinging.  If you have the "octane" gauge on your distributor, you can loosen the "fine" adjustment nut and turn the distributor to advance or retard timing a few degrees very easily.  If you run timing too retarded, you will aggravate overheating issues with the Buick and have really poor fuel economy.  If you run the timing too advanced, the engine will ping and you will damage the pistons.  Backfiring through the carburetor can also be a symptom of over-advanced timing, or mixture that is too lean.

Keep in mind that the manner in which octane is calculated has changed at least three times since these cars were built, therefore references to octane numbers in the manuals are no longer meaningful.  Altitude and fuel quality effect timing.  You should be doing this process with fresh fuel of the type you normally use.  Higher altitude requires a couple of degrees of additional advance;  I am in Colorado using my cars at altitudes between 4000 and 8000 feet.  I run a total advance of 36 degrees without problem on both my antique cars and my old Porsche with conventional ignition.

 

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A couple of minor comments...

 

19 hours ago, 1937 Buick 66C said:

With the engine running at cruising speed (fast enough that both the vacuum and mechanical advance mechanisms are no longer effecting the timing)...

I think the intent here is to have both vacuum and mechanical advance in play (to the extent dictated by the OEM design), so that the total advance at this RPM is set to whatever value is 'dialed-in' on the timing light when the TDC mark is aligned with the reference mark on the engine.

 

19 hours ago, 1937 Buick 66C said:

You want the timing as far advanced as possible without pinging.

My comment here is that the timing resulting from this method may need to be 'dialed-back' (i.e., retarded) somewhat if the starter has difficulty cranking the engine.  This was the situation with my '38 Century when I received it.  It ran fine once it started, but it was a bear to get started.  I currently have the static timing set to the factory spec (6* BTDC) and it now starts easily both hot and cold.

 

That said, I recently purchased an adjustible timing light as Jon described.  I plan to use it to 'tweak' (power tune?) the timing to determine just how much advance it will tolerate before hard starting begins.

Edited by EmTee (see edit history)
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I can not say I agree with "You want the timing as far advanced as possible without pinging" in my case. My car was not pinging at all under an circumstances yet it was surging pretty bad at all speeds and was harder to start when hot and yes a random back fire here and there. I just backed of (retarded) the timing several degrees and she runs like a watch, all the above issues went away. I still have not received my new timing light yet so I'm not sure what my timing is set at but man she runs good. It will be interesting to see what its actually set to. 

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  • 2 weeks later...

Look at the rear of the engine for a little window to view it through. It may have a rubber or steel plug in it. Be sure to verify TDC #1 really is what it says it is. UDC 1&8 means "upper dead center" and is the same thing we call TDC #1 (and #8) now.

 

If the mark is wrong, then someone may have got the flywheel on wrong. I'm told it is possible to install the flywheel in any orientation.

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I cleaned up the line on the window and painted it white also as the flywheel and will try the light on it tomorrow. Is the timing suppose to be set at TDC? Someone else also mentioned it should be advanced some for the electronic points.

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Well, I threw the timing light on the car this morning, no markings are showing when I look through the access hole and the car is idling. So I assume like you said the flywheel was put on in the wrong position. Oh well the car is running great I'm just going to leave the timing where it is and just drive it.

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18 minutes ago, likeold said:

Well, I threw the timing light on the car this morning, no markings are showing when I look through the access hole and the car is idling. So I assume like you said the flywheel was put on in the wrong position. Oh well the car is running great I'm just going to leave the timing where it is and just drive it.

Play with the timing!  Advance a little. An eighth of an inch? Go for a drive. If it "pings", back it off a smidgen.   Another way is with a vacuum gauge. Hook the gauge to a manifold vacuum source, adjust for maximum vacuum.   Most of all , HAVE FUN.

 

  Ben

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I did consider that, I do not have a tach but she is idling pretty low, I will play with it more another day, its getting pretty cold in these parts to be tinkering outside with the car running. All I know is the surging disappeared once I retarded the timing and she is running nice.

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