Random Backfire

[Bloo]

That's fine, but it isn't going to run good anywhere if the advance mechanisms aren't working right, or have the wrong curve. When you get it right at one load/rpm, everything else it could be wrong. It is hard to tell over the internet when you can't hear it, and even when people make videos it is not like being there. I said what I did earlier, because I wondered if the noise @likeold was hearing was the engine kicking back on itself from too much advance. It sounds like that may be the case. I was thinking too much advance from a wrong or defective vacuum advance can. A handheld vacuum pump, a barb, and a dialback timing light can sort that. It is a super common problem on smog era cars, and something I have fixed a lot. In reflection, @EmTee's idea about sticking weights is probably more likely on this car, as vacuum advance and centrifugal advance add under part throttle.

 

One minor thing, no leakage is OK in a vacuum advance. None. If it leaks at all, it cannot control the advance right, and the rip will only get bigger and soon, because it moves every time you hit the throttle. To be fair, some did exist that had an air bleed, but they were smog era dual diaphragm units, and the main section needed to hold vacuum even in those.

 

9 hours ago, likeold said:

Spent a little time on the car today. Disconnected the vacuum advance an hooked up my new gauge to the engine side to make sure it was sucking, yep gauge read 20 when I gave it gas. I wanted to do the suck test on the diaphragm but could not find a 1/8" brass barb so I ran the car an watched the timing marks with my timing light as I revved it up , yep marks would disappear when revved. 

You may be fooling yourself. Trust but verify. As for the 20 in/hg when you gave it gas, that is a normal response, but doesn't really prove much. It is just manifold vacuum except shut off at idle. They do that with a little port right above the throttle plate. When idling, the plate is in open air above the throttle, but open the throttle even a little, and now the port is UNDER the throttle plate, and has in effect moved from open air to the intake manifold. Revving would still move the timing with no vacuum advance. It means something works, either centrifugal or vacuum or both. It won't tell you which.

 

On ANY old car having driveability issues I clean and lube the weights and springs, take the mechanism apart, clean all the crap out where the outer shaft turns on the inner, deburr anything that could cause any of it to stick. I clean up the breaker plate pivots (on your distributor, that is the 3 balls). I oil everything. If you use any grease down below on the pins, it needs to be super light or it causes drag. Dilute the grease with ATF. I check the vacuum advance for leakage, replace if needed. I verify the TDC mark on the engine, and make a new one if it is wrong (this is on the harmonic balancer or the flywheel, depending on which engine it is). It cannot be overstated how important it is to KNOW (not guess) where TDC #1 is. Then I stick the distributor back in the car and verify that what it is doing with the vacuum disconnected matches what the manual specs for centrifugal advance. Then I use the vacuum pump (just at idle or whatever) and check what you see from vacuum advance matches what is in the manual. This is for stock vehicles. If I have to come up with my own specs for a modified vehicle, that is more work.

 

9 hours ago, likeold said:

How do I recenter the octane scale to be centered. Is that an allen screw on top of it to reset? Will I be able to turn the distributor more to low once I center that?

Ill bet that wasn't always an allen bolt. Those octane selectors are a cool looking widget, but fairly useless now that gas is so standardized. Here's how it was done: You start with the octane selector at 0, probably set with the allen bolt. Then, loosen the distributor itself with some other bolt (maybe a clamp bolt?) and set the timing to factory spec using the real timing marks and a timing light. Vacuum advance should not be working at all because the engine is idling. Common practice is to disconnect it temporarily to be sure. Once the timing is set to factory spec with the octane selector at "0", then the "0" represents factory spec, and you can advance or retard from there to compensate for differences in gas.

 

 

[EmTee]

56 minutes ago, Bloo said:

Ill bet that wasn't always an allen bolt.

I'm pretty sure it is on the Buick; if I recall correctly it's either mentioned or pictured in the shop manual.  As I said, my car also has an Allen screw on the pointer.  Although gas really doesn't vary from station to station as in the old days, the selector is still handy for experimentation as once the base timing is set and the pointer is zeroed it allows tuning for peak performance without having to connect a timing light every time to add or subtract a few degrees of base timing.  It's also handy when removing and reinstalling the distributor.  It's more precise than scratching a mark where the distributor flange meets the engine block...

 

Also, note that there's a grease fitting on the distributor to lubricate the shaft bushing.  The book says to lubricate every 1000 miles.  I just gave mine a squirt.  Once everything is working as designed, you should be able to floor the accelerator at 30 mph in high gear and the engine should pull smoothly to 60 mph without any bucking or flat-spots.

[likeold]

Well I have not had my car up to 60 but yesterday 30 to 50 in no time, seemed to have plenty of power and accelerated smoothly with no bucking or hesitation. I'm not sure if its my imagination but it seems the engine sounds very different with the timing retarded so much from its original position. I just wonder why the previous owner had it so far advanced, it ran like crap, I must have turned the distributor back a 1/2" turn or more so far. After I test the vacuum diaphragm on the engine I plan to pull the distributor and check and clean everything.

[EmTee]

1 hour ago, likeold said:

I just wonder why the previous owner had it so far advanced, it ran like crap, I must have turned the distributor back a 1/2" turn or more so far.

That's exactly why I'm suggesting the mechanical weights may be sticking.  I had the same experience with my '38.  I retarded the timing to get it to start without laboring.  I couldn't understand why or how it ran before.  Then I saw the mechanical weights in my distributor covered with surface rust.  My conclusion was the weights were not returning all the way at idle, therefore when I retarded the timing to move it back 'to spec' I unintentionally retarded it too far, because after freeing the mechanical advance the base timing was in fact at TDC, instead of 6* (as specified for the 320).

 

Again, this is why I'm strongly suggesting that you verify the condition of your distributor's mechanical advance mechanism...

[likeold]

Update, pulled the distributor: mechanical weights and springs are working fine. The vacuum advance is junk and and the plate does not turn smoothly even after cleaning and lubricating. The divots from the balls seem to be very minute but most likely are causing the problem. Now what to do next? The balls pushing on the the distributor housing seem pretty tight. By bending the ball carriers back a little might reduce the tension.

[pont35cpe]

Couple ways you could go, Spark-O-Liner ring, Dyna-flyte 880 breaker plate, or the 3 plastic inserts in place of the 3 ball bearings. Maybe someone will list the Delco number for the ball to plastic pivot.

[likeold]

6 minutes ago, pont35cpe said:

Couple ways you could go, Spark-O-Liner ring, Dyna-flyte 880 breaker plate, or the 3 plastic inserts in place of the 3 ball bearings. Maybe someone will list the Delco number for the ball to plastic pivot.

 

Okay thanks, would like part numbers and where buy. I saw a used Dynaflyte on eBay but would like something new if possible and the best option. Also I see a rebuilt vacuum on Cars for $60 is that the best way to go for the vacuum? Thanks.

[pont35cpe]

Those Dyna-flytes model 880s are hard to find anymore. Cars and Bobs both sell the rebuilt vac advance, both usually require a core, or +$35. Here is a `46-49 breaker plate with the plastic pivots, pretty sure it`ll work in your `38 distributor.       https://www.ebay.com/itm/133921295291

[likeold]

1 hour ago, pont35cpe said:

Those Dyna-flytes model 880s are hard to find anymore. Cars and Bobs both sell the rebuilt vac advance, both usually require a core, or +$35. Here is a `46-49 breaker plate with the plastic pivots, pretty sure it`ll work in your `38 distributor.       https://www.ebay.com/itm/133921295291

 

I'm pretty sure the rotor on this engine turns counterclockwise, I read on the directions of the Remy 1914446 that it is for clockwise turning distributor. So with that said not sure it is a fit. 

[EmTee]

I got my rebuilt vacuum advance unit from Bob's (with exchange).  My distributor already had a Spark-O-Liner installed, so I didn't need to anything more there.  Someone just bought seven NOS liners.  See here: https://forums.aaca.org/topic/383537-sold-sparkoliner-distributor-saver-for-buick-and-gm-cars/#comment-2417425  Maybe they'll sell one to you...

 

 

Edited September 6, 2022 by EmTee (see edit history)

[likeold]

Looks like these are sold, but there are a bunch on eBay, would all GM 8 cyl work, Pontiac and Olds? 

And just to be sure I assume one should be able to move the plate with balls smoothly and easily by hand with the vacuum disconnected?

Also should I be able to move the vacuum arm by hand in and out and make it work by sucking on it? Seems pretty stiff, moves just a little.

[EmTee]

36 minutes ago, likeold said:

Looks like these are sold...

Yes, I was speculating that maybe the buyer would be interested in re-selling a set (unless he needs them all)...

 

38 minutes ago, likeold said:

And just to be sure I assume one should be able to move the plate with balls smoothly and easily by hand with the vacuum disconnected?

Yes.

 

38 minutes ago, likeold said:

Also should I be able to move the vacuum arm by hand in and out and make it work by sucking on it? Seems pretty stiff, moves just a little.

Yes; if you have a 'Mitey-Vac' (hand vacuum pump) you should be able to connect it to the unit and draw a vacuum (20 in/Hg).  The diaphragm should pull the arm in and hold vacuum without leaking.  Mine leaked and didn't move through the entire stroke.  Stiff diaphragm is classic symptom and probably means it is also leaking vacuum.

 

It's good that the mechanical weights are free; mine were sticking, so I had both centrifugal and vacuum advance issues with my distributor.

[likeold]

Okay good to know, learning a bunch here. Is the spark-o-liner the way to go for a quick and easy fix? How long do they last, there are several on eBay for sale.

[Bloo]

58 minutes ago, likeold said:

And just to be sure I assume one should be able to move the plate with balls smoothly and easily by hand with the vacuum disconnected?

Might be a bit draggy but should be smooth. Grease the inside of the track where the balls run. Divots that stop the balls are the problem that makes these sparkoliner things necessary. It is probably going to be a bit tighter because of the repair.

 

59 minutes ago, likeold said:

Also should I be able to move the vacuum arm by hand in and out and make it work by sucking on it? Seems pretty stiff, moves just a little.

They are stiff. It should hold vacuum forever. A good 18-20in/hg (quite a bit less probably, see shop manual) should pull it all the way to the stop.

16 minutes ago, likeold said:

How long do they last, there are several on eBay for sale.

I believe they are spring steel, so probably forever unless you allow them to rust. I imagine a broken ground wire could also cause damage because the coil would be trying to find ground through the balls.

 

[EmTee]

4 minutes ago, Bloo said:

It is probably going to be a bit tighter because of the repair.

The ball-spring-holder thingy attached to the breaker plate has enough spring travel that I didn't really notice any resistance to plate rotation.  The plate should move smoothly in the liner.

 

[likeold]

Spark-o-liner and vacuum on order.

[Ugly Rumor]

There is a lot of valuable information here regarding the distributor.  I would certainly remove it and recondition it.  But I would also not neglect the fuel system.  If the car has sat for an extended period of time, you may have rust in the lines that intermittently blocks fuel, or water in the tank.  If thorough reconditioning of the distributor doesn’t work, I’d look there.

[likeold]

Update: Installed new breaker plate, spark-o-ring and vacuum. Put timing on 4 degrees and car now runs worse than before. Backfires a muffled noise in exhaust especially when I let of the gas pedal but sometimes when just cruising. I advanced the timing some and the car begins to chug so I put it back to the book spec. Seems to smell a bit of raw gas when its running. I played with the carb adjustments and found one adjustment screw out 3 turns and the other 1 1/2. I tried to adjust them according to the book, now they are each about 1 1/2 to 1 3/4 turns. What should I look at next?

[EmTee]

Have you looked at manifold vacuum at idle with a vacuum gauge?  If not, I'd probably do that next if timing is set back to 4*.  You can use the vacuum gauge to fine-tune the idle mixture screws.

 

Other things to check:

1. Dwell setting (S/B 30* +/- 2)

2. Did you check the vacuum diaphragm before installing it ("trust but verify")...

3. Was idle speed at 400 RPM when you set the base timing (to ensure centrifugal advance is at minimum)?

4. Does the breaker plate move smoothly and snap-back when you pull vacuum with hand pump and then abruptly release vacuum?  (Just to make sure the vacuum advance pivot screw isn't too tight and the Spark-O-Liner is working as intended.

 

The popping seems to indicate that the distributor timing advance (either mechanical or vacuum) still isn't working as it should.  Do you have a timing light with adjustable advance?  If so, you can try checking the flywheel timing at a couple of RPM points and compare to the distributor advance graph in the shop manual.

[likeold]

3 minutes ago, EmTee said:

Have you looked at manifold vacuum at idle with a vacuum gauge?  If not, I'd probably do that next if timing is set back to 4*.  You can use the vacuum gauge to fine-tune the idle mixture screws.

 

Other things to check:

1. Dwell setting (S/B 30* +/- 2)

2. Did you check the vacuum diaphragm before installing it ("trust but verify")...

3. Was idle speed at 400 RPM when you set the base timing (to ensure centrifugal advance is at minimum)?

4. Does the breaker plate move smoothly and snap-back when you pull vacuum with hand pump and then abruptly release vacuum?  (Just to make sure the vacuum advance pivot screw isn't too tight and the Spark-O-Liner is working as intended.

 

The popping seems to indicate that the distributor timing advance (either mechanical or vacuum) still isn't working as it should.  Do you have a timing light with adjustable advance?  If so, you can try checking the flywheel timing at a couple of RPM points and compare to the distributor advance graph in the shop manual.

 

I did check vacuum at idle before I started all this, it was about 19-20 hg

No points has electronic ignition 

Checked new diaphragm and also put old back in because it seems fine - same results

Yes timed at 400 rpm very low

Plate now moves freely and pops back

 

Keep in mind my symptoms are now slightly different after installing the new parts. It now backfires (muffled pop) when I let off the gas going 30-40 mph and some still when I'm cruising on the flat.

 

I will play with the vacuum gauge and the carb adjustment, what should I look for?

This really still seems like a timing issue still like you say.

[MCHinson]

Personally, I would go back to an original set of points and set everthing by the shop manual specs. I would be suspicious of the electronic ignition. It seems that they tend to be less reliable on 6 volt systems than point are.

[EmTee]

I would typically adjust idle mixture screws to maximize vacuum and readjust idle speed as needed.  Some people suggest leaning-out the mixture a half turn (?) from the maximum point.

 

I forgot about the electronic ignition.  That said, at this point I'd probably try installing a set of points & condenser just to be sure...

 

Ha - Matt Hinson beat me to it! 

Edited September 18, 2022 by EmTee (see edit history)

[likeold]

Yes, I was thinking the same thing. I think I have all the parts the previous owner took out, I will see if I can put it back together.

[likeold]

If someone has a minute and could send a pic of the inside of the distributor points & condenser set up for a 38, it would be helpful to me as I did not install the electronic ignition. Also is there suppose to be a ground wire from the points plate to the casing, I do not have one currently. I'm not sure what wires go where.

[EmTee]

[Bloo]

12 minutes ago, likeold said:

Also is there suppose to be a ground wire from the points plate to the casing, I do not have one currently. I'm not sure what wires go where.

You need that regardless of whether you have points or electronic. You will get random misfiring (and explosions in the exhaust) without it. It is special wire made to take a lot of bending without breaking. I believe they are mixed strands of copper and spring steel.

 

[EmTee]

The ground wire is under the screw that attaches the vacuum advance arm.  The other end screws onto the outside of the distributor body.  The terminal fits into a notch that allows it to pass under the cap.  Look at about 11 o'clock in the photo above.

Edited September 18, 2022 by EmTee (see edit history)

[likeold]

7 minutes ago, Bloo said:

You need that regardless of whether you have points or electronic. You will get random misfiring (and explosions in the exhaust) without it. It is special wire made to take a lot of bending without breaking. I believe they are mixed strands of copper and spring steel.

 

Well holy cow that is whats wrong with my car, I wonder if that's all I need. Why is it needed with electronic ignition? 

[EmTee]

The points, or the electronic transistor switch is periodically grounding the primary wire to the coil.  That's what induces the high voltage output from the coil.  If the points or electronic switch isn't at ground potential, the induced spark voltage will be lower, (i.e., weak) or missing entirely.

[likeold]

16 minutes ago, EmTee said:

The ground wire is under the screw that attaches the vacuum advance arm.  The other end screws onto the outside of the distributor body.  The terminal fits into a notch that allows it to pass under the cap.  Look at about 11 o'clock in the photo above.

I just ran out to my shop and looked in the box for the ground wire. Looks like everything else except the ground wire. Is this something I can buy or do I have to make something? The end that sits on the distributor casing could be tough to create.

[EmTee]

You could make one, but Bob's Automobilia sells them.  I fixed mine temporarily and later replaced it with one from Bob's.  You could take a piece of wire and solder terminal ends on it for a temporary test run.  @Bloo was questioning the end that attaches to the vacuum advance arm pivot because it does seem odd to have it there, but that's where mine was and the new wire from Bob's wasn't long enough to attach it anywhere else on the breaker plate.  The wire then passes through a notch under the cap and the other end attaches to a threaded hole just below the notch.  That connects the breaker plate electrically to the distributor body, which is clamped to the engine block, which is connected to the negative battery terminal.  Without that wire you're relying on those 3 balls to contact the distributor housing.  Adding the Spark-O-Liner makes the balls move more smoothly, but also increased the DC resistance to ground which probably explains why it may actually run worse now...

[likeold]

2 minutes ago, EmTee said:

You could make one, but Bob's Automobilia sells them.  I fixed mine temporarily and later replaced it with one from Bob's.  You could take a piece of wire and solder terminal ends on it for a temporary test run.  @Bloo was questioning the end that attaches to the vacuum advance arm pivot because it does seem odd to have it there, but that's where mine was and the new wire from Bob's wasn't long enough to attach it anywhere else on the breaker plate.  The wire then passes through a notch under the cap and the other end attaches to a threaded hole just below the notch.  That connects the breaker plate electrically to the distributor body, which is clamped to the engine block, which is connected to the negative battery terminal.  Without that wire you're relying on those 3 balls to contact the distributor housing.  Adding the Spark-O-Liner makes the balls move more smoothly, but also increased the DC resistance to ground which probably explains why it may actually run worse now...

All makes sense, well I know what I will be doing tomorrow, thanks I hope this fixes it.

[37_Roadmaster_C]

Another temporary fix would be to use a piece of "Solderwick" or equivalent as the wire. If you do go this way, crimp the terminals on the wick with the insulator removed and a little extra wick going through the crimp. Next, VERY carefully add a LITTLE solder to the exposed end of the wick. Make sure the connection is heated before the solder is added. Expect to goof a few times unless you are an experienced solderer.  As the name implies, Solderwick is designed to absorb solder for desoldering parts from circuit boards. You MUST ensure that the solder does NOT get into the flexing part of the wick. If it does the wick will not be flexible any more and that defeats the purpose of using the wick.

   I have this stuff on hand. If I did not, I would just order the wire from Bobs and wait for the delivery. Fix it once and fix it right 😊.

[likeold]

Worked on the car today made a nice grounding wire for the points plate, took her for a ride and she did run a little better but still have the muffled backfire every once in a while mostly while cruising on the flat about 35 mph. I Put the new vacuum advance back on, re-timed the engine to spec, and adjusted the carburetor with the vacuum gauge. The engine purrs and has plenty of power and runs very well but still has this muffled popping every once in a while in the exhaust. I guess the next thing is to try putting the original points and condenser back in. I will have to research the parts that I have and see if I have everything needed.

[Bloo]

It's gonna do that going downhill, they all do. The better you get it tuned and sorted out, the better it will run and the less noticeable it will be, but it is always there.

[Bloo]

Another possibility if you can't get that wire is to try to modify a Ford one. There was one used on Ford distributors right until the end of points (1975?). Any early 70s Ford has one. Napa should have that in the warehouse if not in the store. It might take some creative bending and hammering of one of the terminals to get it in that slot and bolted down as the Ford wire has plain ring terminals. The ford wire is not insulated, and it doesn't need to be. It is made out of the right kind of wire. Just make sure it doesn't touch anything bare that is on the hot side of the points. It looks like nothing in that Buick distributor is even close, but pay attention to that.

[likeold]

I made what I think is a good one.

[Bloo]

It looks nice, but what kind of wire is it? No matter what It is it will be fine for a little while. If it is ordinary copper it is going to break. That wire bends every time you step on the gas.

 

A long time ago, when I was a dumb kid working in a gas station, I won an old truck in a drawing. One day, while driving to work, it started running terrible, and got worse and worse. The explosions were getting loud, but I kept it revved up at lights and floored when I was moving because it seemed obvious it wasn't going to get me to work. It did, but the explosions were probably heard in the next county. We pushed it into the shop, and the mufflers, glasspacks, were blown wide open along the weld. Those aren't sheetmeetal you know, they are heavier steel. They were unrolled and looked like a couple of gutted fish. Someone had made a replacement for that wire out of regular copper wire and it broke. I replaced it with regular wire again (it was probably Sunday or something). I put in 3 complete loops of wire in the bottom of the distributor and soldered the terminals on, so as the wire bent it would wind more like a spring and the angle at the ends wouldn't change much. It lasted, and when I got that same truck back around 2014, the wire was still in there and still working.

 

You don't have the option of looping it in the Buick. Your advance weights are down there under the breaker plate. In the truck the advance mechanism was up high under the rotor so there was plenty of room without interfering with anything.

 

[EmTee]

Your home-made wire will be fine until the new one from Bob's shows up.  I want to say that I also notice a muffled 'pop' from my '38 once in awhile.  I don't know, or haven't yet noticed anything in common among those events.  It seems to randomly occur on occasion.

[BuickBob49]

Move the plug wires on the distributor one hole over and see what happens. Maybe someone got them off one hole. Don't ask me. I know on my 1949 Super. It got me right in the morning middle of the timing band.

 

Edited September 19, 2022 by BuickBob49
Clarify (see edit history)