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1941 Buick Limited Limousine


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Matt,

It's like a 'corona mask" for your rocker arms.

Sits above the rockers on the two studs that secure the valve cover.

Made in Winder,, Georgia about half way between Atlanta and Athens.

Maybe Lamar , AKA  "Mr. Earl" could run over and pick one up for you.

 

Mike in Colorado

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15 minutes ago, Dynaflash8 said:

Matt:  Up until most recently all of my trouble with ethanol gas has been with my '39 Buick.  It gets really hot here in south central Florida.  I'm not sure what is going on with the '41.  I haven't been able to get out of the house for nearly a month now.  Anyway, with the '39  I can be running along 55-60 on the highway on a day in the high 80s or 90s and it will simply run out of gas.  I turn on the electric fuel pump and it starts up right away and goes on.  Also, if I stop for gas or at a store, the old '39 will start right  up and go about 100 feet and run out of gas.  I have to restart it with the electric fuel pump.  One problem I can see is that the steel gas line runs from the fuel pump on the right side of the engine across in front of the engine to the carburetor on the left side of the engine.  Where it crosses over it is clamped into a metal clip that is bolted to the cylinder head right at the thermostat housing.  I improved the car somewhat with the use of a foam sandwich from Home Depot that is designed to use on home water heater pipes to keep them from freezing in winter.  I have found a 1941 Limited 90F in driver condition.  It's probably too late for me now since I'm 81.  And, my Roadmaster is finished.  I got the Limited declared Full Classics back in 1974 or 1975 by myself.  The Roadmaster took until 2018, with help from Doug Seybod, Terry Boyce and I guess others, but in any case now it is a Full Classic too.

 

In 1941, fuel probably had a boiling point far higher than today's gas (maybe 250 degrees vs. 150-160 today). That's why old cars have heat risers under the carburetors--they NEEDED to be hot to atomize that gas. Today we have the opposite problem and the gas practically evaporates almost at room temperature. All that heat the engineers designed into the system fights us when using modern gas. It isn't because your car is broken or defective or needs someone to tune it properly or anything like that--it simply was designed for gas with a very high boiling point. That isn't your fault or a shortcoming in the hardware.

 

What you're describing there, Earl, is textbook fuel boiling--exactly the sort of thing an electric fuel pump is designed to fix. You can alleviate some of it with insulation, but the problem is that it's actually boiling inside fuel pump and carburetor bowl. Keeping the lines cool may help a little bit, but as I described, when you're cruising along and everything is running at 2000-3000 RPM, there's plenty of pressure in the fuel lines, a good supply of fresh cool gas from the tank moving through the pump, air wooshing through the engine compartment, and, most importantly, the atomizing fuel in the carburetor actually sucks heat out of the carb itself (vaporization is an endothermic reaction, meaning that it absorbs heat rather than making it). Ever wonder how carburetors can freeze on a hot engine even when ambient temperatures are above freezing? This is why. At speed, there are no problems because everything is nice and cool and the fuel is moving through the system at a reasonable rate. It just doesn't have time to absorb heat.

 

At idle or when you shut off the engine, all that stops. Temperatures skyrocket almost instantly. There's no fresh, cool fuel flowing through the fuel pump and lines. And since the carburetor is at idle, the endothermic effect is greatly reduced as well. Everything gets really hot, really fast and the small amounts of fuel in the pump and carburetor can start to boil and turn to vapor. Since a mechanical pump can't suck liquid through vapor, that's why you run out of gas. The carburetor bowl has enough gas (liquid and vapor) to start the car and drive a few feet, but there's no fresh gas coming in because the vapor in the pump and lines can't pull fresh liquid fuel from the tank. The result is you seem to run out of gas until you turn on the electric pump, which PUSHES fresh, cool, liquid gas through the system from the back.

 

Be aware of the circumstances that cause the problem and activate the electric pump when you know you're facing one of those situations. That should help a great deal.

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36 minutes ago, Dynaflash8 said:

One problem I can see is that the steel gas line runs from the fuel pump on the right side of the engine across in front of the engine to the carburetor on the left side of the engine.

That is not the problem.  Vapor lock occurs on the suction side of the fuel pump...any pump will push fuel and any vapor, but cannot pull vapor.  That is why the electric pump needs to close to the tank.

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As a sidnote to the vapor lock discussion:  

 

I have had to insulate the fuel line and also wrap the exhaust on everything we have had with fender skirts - just retains too much heat under car at the hump for the back axle in relation to the quality of the gasoline. 

 

Sorry, I do not have a photo, but on a fuel line  I have been using  2 inch or so exhaust wrap and using it length wise with binder clips to hold the ends/edges together about very 3 inches or so - works great and on a really early car looks very appropriate too (also can be removed easily enough) - I get brass clips for brass era cars and nickle plates clips for newer cars.

 

https://www.staples.com/OIC-Brass-Plated-Round-Head-Fasteners-3-8-Head-1-Capacity/product_378814?cid=PS:GooglePLAs:378814&ci_src=17588969&ci_sku=378814&KPID=378814&gclid=Cj0KCQjw4dr0BRCxARIsAKUNjWT5uxJ6Jus-e7wCaDybWnNrLsf6b8YVlWP54J0fRhjfBtyGKrFPE08aAniqEALw_wcB

 

John

Edited by John_Mereness (see edit history)
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John is right.

Here is what I did on my '40 LTD.

Re-routed the fuel line and covered it with rubber hose.

Wrapped the exhaust with heat tape, from the base of the carb, past the master cylinder, clear to the muffler.

Also installed an electric pump on a switch, and a BIG clear filter back at the tank.

Because, up here at 8500 ft. the dreaded "vapor lock" is a way of life.

We're constantly either going up a hill or down a hill.

Up is worse, and some of the pulls are 10 - 15 miles long.

And finding no ethanol fuel is impossible.

So I don't think of the changes I made as violations, I look at them as enhancements to my "driver".

 

Mike in Colorado1660457208_finaldump044.thumb.JPG.df23b3d438e263b9bf5ba455926a54b2.JPG

Edited by FLYER15015 (see edit history)
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3 hours ago, old-tank said:

That is not the problem.  Vapor lock occurs on the suction side of the fuel pump...any pump will push fuel and any vapor, but cannot pull vapor.  That is why the electric pump needs to close to the tank.

Good information.  Mine on the 39 is near the X-member.  Seems to work okay.  I'm not sure where they put the one on the '41, but I'll have that checked.

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3 hours ago, Matt Harwood said:

 

In 1941, fuel probably had a boiling point far higher than today's gas (maybe 250 degrees vs. 150-160 today). That's why old cars have heat risers under the carburetors--they NEEDED to be hot to atomize that gas. Today we have the opposite problem and the gas practically evaporates almost at room temperature. All that heat the engineers designed into the system fights us when using modern gas. It isn't because your car is broken or defective or needs someone to tune it properly or anything like that--it simply was designed for gas with a very high boiling point. That isn't your fault or a shortcoming in the hardware.

 

What you're describing there, Earl, is textbook fuel boiling--exactly the sort of thing an electric fuel pump is designed to fix. You can alleviate some of it with insulation, but the problem is that it's actually boiling inside fuel pump and carburetor bowl. Keeping the lines cool may help a little bit, but as I described, when you're cruising along and everything is running at 2000-3000 RPM, there's plenty of pressure in the fuel lines, a good supply of fresh cool gas from the tank moving through the pump, air wooshing through the engine compartment, and, most importantly, the atomizing fuel in the carburetor actually sucks heat out of the carb itself (vaporization is an endothermic reaction, meaning that it absorbs heat rather than making it). Ever wonder how carburetors can freeze on a hot engine even when ambient temperatures are above freezing? This is why. At speed, there are no problems because everything is nice and cool and the fuel is moving through the system at a reasonable rate. It just doesn't have time to absorb heat.

 

At idle or when you shut off the engine, all that stops. Temperatures skyrocket almost instantly. There's no fresh, cool fuel flowing through the fuel pump and lines. And since the carburetor is at idle, the endothermic effect is greatly reduced as well. Everything gets really hot, really fast and the small amounts of fuel in the pump and carburetor can start to boil and turn to vapor. Since a mechanical pump can't suck liquid through vapor, that's why you run out of gas. The carburetor bowl has enough gas (liquid and vapor) to start the car and drive a few feet, but there's no fresh gas coming in because the vapor in the pump and lines can't pull fresh liquid fuel from the tank. The result is you seem to run out of gas until you turn on the electric pump, which PUSHES fresh, cool, liquid gas through the system from the back.

 

Be aware of the circumstances that cause the problem and activate the electric pump when you know you're facing one of those situations. That should help a great deal.

Thanks for that infor Matt.  What about running out of gas at 50-60 mph on a high 80s to low 90s outside temperature?

 

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4 hours ago, Dynaflash8 said:

Thanks for that infor Matt.  What about running out of gas at 50-60 mph on a high 80s to low 90s outside temperature?

 

 

Could be a weak diaphragm in the fuel pump combined with higher temperatures and speeds. 

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8 hours ago, Matt Harwood said:

 

Could be a weak diaphragm in the fuel pump combined with higher temperatures and speeds. 

Thanks Matt.  It is okay on regular gas.  Anyway, it has had this problem in Florida over several different fuel pumps.  I guess it could be possible the rebuilder isn't using a different diaphragm.

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The boiling point of fuel can be increased with the addition of kerosene. It is a useful additive in the prevention of vapor lock. Not sure of the ratio but it was previously discussed and I remember there was info regarding how much to add so a simple forum search should bring it up.   

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Posted (edited)

Replacement fan belt is a no-go. Measures the same as the Gates belt, but I spent two hours this evening trying to fight it on there, bending a bunch of radiator fins and shredding my shirt on various sharp things under the hood, and it just would not go over the crank pulley. Part of it is that it is VERY stiff and would not bend easily, and part of it was that I couldn't really get my hands in there to maneuver it into place. The Gates belt slips right on in two minutes. Grrrr...

 

I took some photos, but they're on my cell phone which fell into the bowels of the engine bay and I went home without it.

 

 

Edited by Matt Harwood (see edit history)
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well at least it wasn't expensive and you gave it the ole college try. keep pluggin' away at it. as you told me, "if it goes sideways walk away and come back to it later".

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Matt I have used a heat gun and also hot water soak to soften up a stiff belt and anything rubber that was to stiff to install. Also slipping a piece of cardboard behind the radiator takes the pain of knuckle scraps and fin damage away. I recently changed a belt that would have been impossible for me with my arthritic hands without heating it up..lubed it too to get it under the crank pulley. The tooth back belts are much easier but they are not as quite as you have found though belt dressing helps some. 

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1 hour ago, Matt Harwood said:

and it just would not go over the crank pulley.

 

Can't the generator be moved in further by removing the one bolt in the adjuster bracket?

 

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You may have to do that. On some cars it is just necessary. The proof of correct belt size comes when the adjuster winds up out in the middle somewhere with a reasonable amount of adjustment left.

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4 minutes ago, JohnD1956 said:

 

Can't the generator be moved in further by removing the one bolt in the adjuster bracket?

 

 

I didn't get that far. Just around the water pump pulley. Couldn't get it around the crank pulley. I ordered the next size up to see what happens. I can't live with that noise.

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Do the crank pulley first, and the water pump last. You may literally have to take the generator loose and tip it forward. In that case, do the generator last. It is unlikely that more than one size belt can work given how short the adjusters are on most old cars. I wouldn't run a whole bunch of tension.

 

If it winds up somewhere in the first half of the travel with a new belt, you probably have the right one. When it breaks in it will need to be adjusted. If you are starting out on the last third of the adjuster, there is a good chance you will run out of adjuster when the belt breaks in.

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26 minutes ago, Bloo said:

Do the crank pulley first, and the water pump last. You may literally have to take the generator loose and tip it forward. In that case, do the generator last. It is unlikely that more than one size belt can work given how short the adjusters are on most old cars. I wouldn't run a whole bunch of tension.

 

If it winds up somewhere in the first half of the travel with a new belt, you probably have the right one. When it breaks in it will need to be adjusted. If you are starting out on the last third of the adjuster, there is a good chance you will run out of adjuster when the belt breaks in.

 

Unfortunately, doing the crank pulley first wouldn't work since the belt needs to go over the fan. The Gates belt leaves the generator in about the middle of its travel, so I figured this belt, being only about an inch smaller, would fit. The Gates belt is about 52 inches around the outer perimeter and this one is 51. I spent some time reading and thinking about it, and the new one is slightly thicker than the Gates belt, and that might affect the inside circumference of the belt in a significant way. Although it's only 1 inch on the outside, it might be several on the inside.

 

I checked with Bloo's source, above, but they don't offer one that's close to the 52 inches. They have a LOT of options, but there's a conspicuous gap right in the sizes I need.

 

I'll get Roman, my  mechanic, to help me in the morning. We'll remove the hood so we can get to both sides simultaneously, use a heat gun, and see if we can maneuver it on there with both of us working. If not, we'll try the replacement I ordered tonight. That one is 54 inches around the outside but it might be a little closer to the Gates belt on the inside since it's a bit thicker. I figure that extra two inches is still within the adjustment range of the generator brackets. If not, well, I'll just use the Gates belt and live with it. 

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1060076734_2020-04-1618_37_50.thumb.jpg.16a5946936326991210b24ad60308407.jpg826967582_2020-04-1618_38_06.thumb.jpg.53b02e03bf44267c2ae31bec10a6bf13.jpg

 

Hopefully the next size up will be closer to fitting properly. This one looks close at a glance, but given that it's thicker, it has a smaller inside perimeter than the toothed belt. That has to be part of the problem in addition to the lack of flexibility. I'll just wait for the replacement belt instead of wrestling with this one anymore. I have other jobs to do this weekend anyway, so I'll reinstall the toothed belt and work on other things instead.

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I like that but it's not fair, there's no fan... but then you say it was for the humour of it didn't you. 😃

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OSHA approved method? I think the clip should be marked “don’t try this at home” I keep thinking of the Jackass movie clips.

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So this happened this morning:

 

733186550_2020-04-1608_32_44.thumb.jpg.259b8914e10b472a3d48158a8cb56ff9.jpg

 

That kind of sucks, so there will be no test drives or any road work today. Meh.

 

Instead of trying to do more tuning and installing these new, hotter spark plugs I found, I decided to tackle the turn signal indicators in the dash. They've never worked, despite replacing bulbs. As I've mentioned before, someone in the past bought a beautiful new wiring harness and then proceeded to hack it up so things would work (or not) the way he thought they should. I already had a fight with this idiot's work on the interior lights, and I discovered today that he was at work on the turn signals as well. Most of the wiring is correctly colored cloth-covered wiring that's recent, but the wires coming from the turn signal switch inside the steering column are plastic. Two orange, two white, and two black. Lord knows where they're connected or what they do...

 

I should point out that my exterior turn signals work correctly, just not the green arrow indicators on the dash. I checked the wiring diagram and it was a little confusing at first. It appears that there are six wires coming out of the switch in the steering column: two for the blinker relay, and one for the left exterior indicators, one for the right exterior indicators, and one each for the dash indicators. I got confused initially when I saw a three-wire connector which feeds all the right-side indicators but not the left-side indicators. The left side are fed directly from the switch in the column. 

 

WiringDiagram.thumb.jpg.ecec376c9abf65e788e436470230283c.jpg

Turn signal wiring seems straightforward...

 

I decided to start with the three-way connector and started tracing wires. They all seemed to be connected but the dash indicator wouldn't work. So I took the connector apart and had my A-HA! moment. One of the wires, presumably the one for the dash indicator, had come loose inside the housing:

 

TurnSignal1.thumb.jpg.03494124930e964602b98553b9486754.jpg

One of the wires was loose inside the 3-way

connector. Surely this is the problem, right? Wrong.

 

I connected that loose wire to the third pin where it had obviously been soldered at one time and... nothing. No change. I found that by touching it to the adjacent wire, everything worked correctly, including the dash indicator. That didn't make any sense, but I wasn't going to argue. I soldered the two wires on the same terminal, closed up the connector, and hooked it all back up. Now I had a working right side dash indicator. Nice!

 

The left side was a bit more of a challenge because there was no connector, just wires hastily spliced together using those crappy blue plastic butt connectors. Man, I hate this guy. None of the wires were connected the way the wiring diagram suggested they should be and it looks like he ran the wire intended for the dash indicator forward to the parking lights instead. I snipped a few of his connections and tried rearranging the six wires in various combinations but could not make all three indicators work. Either the external ones worked OR the dash indicator worked, but not both at the same time. I did some more testing and probing and found that two of the six wires coming out of the switch in the column were not connected to anything. Hmmmm...

 

Striking out trying to get the existing wires to do their jobs, I decided to cheat and just run a wire from the junction block up on the fender that feeds the front turn signal. I could hide the wire, it's a straight shot, and it would definitely work. I added an eyelet to one end of a black 14-gauge wire and hid it under the wire for the parking light on the junction block, then tucked it into the main wiring harness bundle that runs back into the dash. Nobody will ever see it. Under the dash, I connected it to the wire that feeds the dash indicator. Voila! Working turn signals all around!

 

I fired the car up to charge up the battery (I was testing lights all day and had the doors open with the interior lights on most of the time) and saw that the left side dash indicator was flickering slightly. Not full-on but enough to be visible even in daylight:

 

 

If I had to guess, I would say that the generator is inducing a slight current in the wire I ran from the parking light terminal to the dash indicator. Since I tucked the new wired in to the existing harness, there must be just enough electromagnetic noise from the generator's primary wire to induce a tiny current in the new wire. The green LED in the dash literally takes one or two milliamps of current to illuminate--even that tiny amount of electrical noise is probably enough to cause it to flicker. 

 

I'm not an electrical engineer, but I wonder if I can add a resistor in the wire that will prevent this stray current from bleeding through to the LED. When turning on the turn signal, the greater current from the parking light terminal should illuminate the LED as normal, even with a resistor in place. Perhaps something like a noise suppressor for a radio would work? I could also try running the wire on a different path away from the generator wire, but I like it hidden so it looks as correct as possible. 

 

Does it matter than I'm using a solid-core wire rather than stranded for the turn signal indicator (I used solid core simply because it would be easier to push through the wiring harness loom)? I'll do some reading and see if there's an answer.

 

For now, however, I'm finally on the verge of having every light in the car operating correctly. 

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In the old way of doing things, the flasher has a third terminal for the indicator light. It's purpose is to blink an indicator light, one only for both sides (not an individual right and left like you have).

 

If your brake lights are completely separate from the signals, and I believe they are on a 41, all you need for signal lights is one SPDT switch. It connects all of the right (or left) bulbs to the "load" terminal on the flasher. Since Buick had two indicators, they could have just connected them to the rest of the signal lights right there at the switch. I cannot imagine why they didn't.

 

I believe what I am looking at on your scan of the wiring diagram is a DPDT switch. The right side operates as described above. On the left, I believe they took the flasher's indicator terminal and switched it right/left with another set of contacts.

 

Sounds like you got it working though. Connecting the indicators to the signals is how it is done in newer models. Also, all 3 pin flashers are not created equal. Sometimes that third indicator pin doesn't do exactly what you would have expected it to do in 1941.

 

Stranded wire is used only for mechanical reasons. It is less prone to fatigue and breakage. The electricity will not care at all.

 

I can't even guess about the LEDs. I have been watching your LED posts with interest over time, planning to copy you at some point, in order to brighten the tail/stop lights, and also take a little load off my generator. LEDs are funny beasts. As you noted it takes very little to light them up. I suppose it could be coupling from another wire, but I'll bet it is just noise on the whole electrical system.

 

I have seen spikes of over 200 volts on the electrical systems of 12 volt 1960s-1970s cars, apparently due to collapsing magnetic fields (ignition systems, horns, relay coils, voltage regulators, and so on). Cars with electronics have little resistors, diodes, etc. all over the place to control it. My 6 volt Pontiac is so noisy that digital test instruments wont even work on it.

 

I gather the right side dash indicator is working on the original wiring? If so, and the left side isn't, that would have to be a problem with the switch. I believe those left side terminals are a simple SPDT switch. If so you should be able to hook it up Buick's way and not have that long wire picking up noise. Maybe the switch needs repair.

 

I doubt a series resistor would help. Maybe a resistor to ground, though I don't know how much current it would have to draw to solve this. Maybe even a small capacitor to ground.

 

 

 

Edited by Bloo (see edit history)
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9 minutes ago, Den41Buick said:

Green indicator lights? I have never seen those before.

 

They're supposed to be green. Buick used little green lenses inside the housing to make them green, but over time the sun washes out the green. Check out Neil's '41 Super thread and you'll see the lenses he took out of his instrument panel--the shape of the arrow was neatly faded away on the otherwise green lens. Using green LEDs is a simple solution.

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19 hours ago, Matt Harwood said:

 

 

For now, however, I'm finally on the verge of having every light in the car operating correctly. 


 

Customer: What do you mean you have 87 hours making all the lights work at XXX dollars per hour? 
 

Fixing old cars isn’t terribly difficult, it just takes time. Fixing a car that has had a half assed tractor mechanic hack the sxxt out of it? Almost impossible. On top off all that, finding a true talented craftsman that can fix it? Almost impossible at any price. Car value? 20k, cost to sort it so everything works properly? 20, 30, 40k.......easy, and that is NOT restoration work. That is repairing and sorting the car so you can actually drive it. Been there, done that. Do yourself a favor, buy a car that you can drive 250 miles in one day in 95 degree weather without ANY problems..............no matter what you pay, it will be a bargain. Ed

Edited by edinmass (see edit history)
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Well, I found a more "local" wire under the dash to feed the signal indicator and it still flickers. Hmmm. It has to be some noise in the harness somewhere, but it doesn't affect the right side. I'm going to contact the LED company and see if one of their in-line resistors would be able to attenuate the stray current. 

 

Dang.


And as long as I'm messing with wiring, I also reversed my lo/hi beams. They were backwards, so when I had the lo-beams on, the indicator on the dash was lit, and hi-beams turned it off. It's been that way as long as I've owned the car but I keep forgetting about it until I'm driving at night. So I swapped the wires on the terminals out under the hood and now they work correctly. So at least one little win.

 

Tomorrow we install the new hotter spark plugs and fix the accelerator pump rods on the carburetors--still a bit of a stumble that I want to fix.

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17 minutes ago, Matt Harwood said:

Well, I found a more "local" wire under the dash to feed the signal indicator and it still flickers.

 

Can it be on a separate contact on the switch as the diagram you posted shows? Or is the switch just hosed? If so maybe it could be fixed?

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Posted (edited)
12 minutes ago, Bloo said:

 

Can it be on a separate contact on the switch as the diagram you posted shows? Or is the switch just hosed? If so maybe it could be fixed?

 

I don't believe the switch inside the steering column is original. It only has four wires instead of six and one doesn't seem to be connected to anything. So my guess is that the hack mechanic who also ruined my dome light wiring, my seat wiring, got the headlights wrong, and messed up the radio, also screwed this up. He eventually got the signals to work on the outside of the car, but my guess is that the dash indicators never worked for him and he didn't know why. By tracing wires I was able to find the right wires to make the right dash indicator light up, but there is no wire for the left indicator, just a dead stub of wire. 

 

So it's not technically broken, but I'm not sure I want to tear into the steering column to replace the switch, which I think is a more modern unit. As I said, everything works correctly and if I have to, I can live with the flickering. It's not visible in daylight, just in the shop or at night.

 

I contacted the company that sold me the LEDs and asked them about one of their in-line resistors. The resistors are designed to provide enough resistance to make the blinker relay work correctly when using LEDs. Mine works fine because I kept incandescent bulbs in the parking lights, which is enough resistance for the flasher. But my thought was one of these resistors would perhaps attenuate the stray current running through the wires. It's only a milliamp or two, it should be able to block that stray current but let in the true signal from the switch when the signal is on. I'm not an electrical engineer, but that's how I hope it works.

 

 

Edited by Matt Harwood (see edit history)
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Matt, your 41 is too new for me, so I have never worked on one, but have driven several. Is it possible to wire it so both flash at the same time regardless of a left or right turn? At least you will know if the signals are on and not have any flickering. 

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I spoke with the folks at the LED store and they recommended a load equalizer that goes in-line with power to the LED and to ground. It's technically designed to emulate an incandescent bulb's resistance so turn signals work correctly, but he thinks it should also attenuate the flutter. Heck, they're only $2.40 each, so I bought three--one for that one indicator bulb in the Limited and one for each of Melanie's Chrysler taillights, which blink much too fast (a common issue with LEDs replacing incandescent and exactly the problem the equalizers are designed to fix). They'll be here by the end of the week and we'll see if it helps. Like I said, if I have to live with the flicker, I can. It's not visible in daylight.

 

On to other things:

 

On 4/13/2020 at 11:30 AM, Lawrence Helfand said:

I am trying to see what of the three holes your pump rods are attached. Looks to be the middle hole? If so I suggest you use the top hole for the least amount of throw and less fuel from the accelerator pump. The stumble should diminish even more or go away. A slightly higher idle helps as well. This low rpm stumble went away when I swapped the AV 16's for Carter 518's from the 248 motor and in general the motor is crisper in every way and less timing advance sensitive at low rpm. I am convinced the ultimate setup is with the smaller series carbs. Hope you and yours stay strong and healthy and cruising! Lawrence

 

I took Lawrence's advice and tinkered with the accelerator pump linkage on the carburetors. There are indeed three positions and both of my carburetors were set to the middle position, which I think is probably the default setting. Here's a crappy photo of one of my junk carburetors showing the three holes and the linkage (it's the best I could find, sorry):

 

CarbLinkage4.thumb.jpg.467672a58ace69c661ca3f3b7f539d45.jpg

Accelerator pump adjustment is via three holes on the linkage.
Default setting appears to be the middle hole.

 

More curious was that the rod from the accelerator pump to the linkage on my original (now rear) carburetor was mounted on the OUTSIDE of the linkage, while my freshly rebuilt front carb had it located on the INSIDE of the linkage (same as the carburetor in the photo above). Again, I presume that's the correct way to do it, so I reversed the rod and moved it to the upper hole as my friend Lawrence recommended. I did the same for the front carburetor, then went for a test drive.

 

CarbLinkage1.thumb.jpg.7b87003923bf6f9a00ecf9c1bd02bd6b.jpg  CarbLinkage2.thumb.jpg.cc05fdb2cd3288b15c960092d261e7a5.jpg
Rear carb linkage was mounted to the outside of the linkage. Due to the angle, I

don't think it was working properly. I switched it back and moved it to the upper hole.

 

CarbLinkage3.thumb.jpg.726fd850fd77397ec4a19c569e8d02a3.jpg
Front carburetor had the rod correctly located.
I also moved this one to the upper hole.

Should I be concerned about the amount of
leakage on the freshly rebuilt carb after only a

few thousand miles of driving?

 

At best it was unchanged, but I think it was actually worse with the accelerator pumps in the upper hole. It still had that low-speed stumble that I can't seem to get rid of. Part of the problem is surely that it's really cold outside--I was doing my test driving this evening as it was snowing and the temperature gauge was moving slowly between 150 and 160 degrees as the thermostat cycled every 20 or 30 seconds. Glad the radiator is so efficient, but I think the engine needs more heat for a proper tune. Anything I do right now isn't helping.

 

Nevertheless! Since changing settings is so easy, I flipped the accelerator pumps to the lowest holes and took another drive. And how about that, it's quite a bit better! Not perfect, but I dragged it down to about 5 MPH in high gear and it pulled away fairly cleanly. Accelerating from a stop sign on the roll in 2nd or 3rd and launching from a stop in 1st gear were improved. Again, still a bit of hesitation and stumble, but better. I think I'm on the right track and perhaps my car wants more fuel than it's getting, not less. I still suspect that a 180 degree thermostat is what this car wants, but it's too soon to make that call.

 

Until it's 75 or 80 degrees outside, I don't think I'm going to get a proper tune on the car; I'm just being impatient. Maybe I'll go back to work on the Lincoln's engine while I wait for the weather to warm up a bit...

 

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@Matt Harwood  my 56 has that same off idle stumble.  Except when it is cold.  Then it is smooth.  I presume that the choke is still partially closed at that point and the engine is running a little richer.  I believe Jon the @carbking has recommended enriching the idle by enlarging the idle ports in the carb's venturi.  I have not done that, yet.  Most times I can feather the gas past the stumble and keep going. However if there is ever a need for and aggressive start I can usually brake start past the stumble too.  But that's easier said, and done, with an automatic trans.  

 

Also I used to run a 160* thermostat in my car till around 2003.  I never used the car that much and it seems it often had fouled spark plugs.  In 2003 however, I switched to a 180* stat and have not had that problem since.  The temp gauge does run a bit higher which still gives me momentary pause when I see that.  But it's not overheating and it just seems happier at the 180* setting.  

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Matt, I run a 190 in my '50  263.  

  Years ago[ too many] an old to me mechanic told me all engines ran better at around 200. The controls of that day,  the 70's, just were not good enough for the every day driver to run that hot, therefore 180 was the default design. True?  I don't know but I have run nothing colder since.

 

  Ben

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Matt - hesitation from idle can be a number of issues (including timing); however, IF the culprit is the carburetor:

 

(1) The dynamic A/F mixture is too lean

 

OR

 

(2) The dynamic A/F mixture is too rich

 

Sounds simple, and it is. Testing (which you have done) will reveal which condition exists.

 

Since you moved the pump operating rod from center to top to bottom; you found the smallest volume pump shot (top hole) caused the most hesitation; while the largest volume pump shot (bottom hole) caused the least hesitation. So the dynamic A/F mixture is too lean.

 

This is quite often a minor but annoying issue using modern fuel, and many do not understand the function of the idle circuit.

 

For decades, I have mentioned that the "idle mixture screws" are mis-named; as they do not change the idle mixture.

 

Consider the controls to an old-fashioned shower head (three controls). One is cold water, one is hot water, and the third is volume.

 

Now, apply this concept to the idle circuit in MOST carburetors. The cold water represents the idle air bleed, the hot water represents the idle jet, and the volume represents the idle mixture screw(s). So the mechanic CAN change the amount of air/fuel volume with the idle mixture screws, but the ratio remains the same.

 

In the shower example, the bather may control the temperature (A/F ratio) by changing the setting of either the cold water faucet or the hot water faucet. Without modifications, the A/F ratio may NOT be controlled by the mechanic, as both the idle air bleed and the idle jet orifices (sizes) are fixed by the carburetor manufacturer.

 

Not getting into a treatise on ethanol (E-10) here, other than it has less energy than gasoline; and its possible that with all of the other additives non-ethanol fuel also has less energy than 1940 gasoline.

 

The mechanic CAN change the A/F ratio by oversizing the orifices of the idle jet(s). By slightly enlarging the idle jet(s), the idle mixture is slightly richer, which helps the dynamic mixture to be slightly richer when the throttle is opened, thereby reducing or eliminating the hesitation.

 

Typically, on older vehicles, enlarging the idle jet(s) orifice by 0.002 does the trick.

 

On modern modified engines (Pontiac 400 with a four barrel where the owner just had to have the rumpa, rumpa, rumpa of a ram air IV camshaft is a good example), we have occasionally had to enlarge the jets (0.001 per iteration) as much as a total of 0.006 inch to eliminate the hesitation. 

 

Now back to my comment about the idle circuit in MOST carburetors. During the mid-1950's through the mid to late 1960's, some carburetors had an adjustable idle air screw to control idle RPM. These things are an absolute nightmare to adjust to modern fuel; but do have one redeeming function. We generally suggest to customers having this type of idle circuit (mostly GM, but other makes dappled with it), to simply add the curb idle screw found on carburetors without the big air screw. Now the air screw is exceptionally useful for customers that insist on racing camshafts on the street. Think of the holes drilled in the throttle plates to allow adjustment of the angle of the throttle plate at idle, which is turn controls idle air velocity inside the carburetor. The big air screw now becomes an adjustment for the mixture, while the added curb idle screw allows for adjustment of the idle RPM.

 

Jon.

Edited by carbking (see edit history)
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On every Stromberg we build we open up the idle circuit...........modern fuel and E-10 are definitely a challenge, and overall most cars I come across are running lean..........probably 70 percent. Most of what I have learned over the last forty years is from real world testing on an engine or chassis dyno. Early on in the 80’s we were making jets, air bleeds, and other assorted parts just for ourselves. It quickly became apparent that our stuff was running better than most others on the road........we turned it into a business. We ended up going to national meets and offering an on the spot service recalibrating carbs and ignition systems and were able to pay our way for the entire meet/show while we were on vacation. It enabled us to do many more shows and at longer distances than we would have done without offering the service. Doing a super tune or extensive sorting of any pre war car is time consuming. The good thing about it is once you get it right, it stays there. The last ten percent of performance related to fuel, ignition, steering, suspension, and other systems will  make an old car turn from a “tractor” into an automobile. I will have spent the entire month during lockdown working about 100 hours On just one car..........and it’s now almost so good as I can get it. Making my final adjustments over the last day, a new hot start issue has popped up........."there’s no free lunch”, ten steps forward and two steps back. Today will be dealing with the hot soak issue.

Edited by edinmass (see edit history)
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18 hours ago, carbking said:

The mechanic CAN change the A/F ratio by oversizing the orifices of the idle jet(s). By slightly enlarging the idle jet(s), the idle mixture is slightly richer, which helps the dynamic mixture to be slightly richer when the throttle is opened, thereby reducing or eliminating the hesitation.

 

Typically, on older vehicles, enlarging the idle jet(s) orifice by 0.002 does the trick.

 

Jon.

 

Thank you, Jon! Once again, your insights provide a great deal of useful knowledge that we can put to work right away. I'm going to wait until the weather is warmer before doing anything drastic on my carbs, but I think your logic is correct--even with two carbs running synchronously, it still wants more fuel at throttle tip-in. If your recommendation is enlarging the idle jet orifice by two thousandths, I'd be willing to give it a shot.

 

Which leads me to my next question about terminology--which is the idle jet that you mention? Referencing the diagram below, the manual mentions idle air bleeder (5), idle tube (6), idle needle valve (14), and the idle discharge holes (15). Which one should be enlarged as you describe? Don't worry, I'm not going to tear it apart and start drilling holes, but I might dissect one of my scrap carburetors and see what the parts look like.

 

StrombergDiagram.thumb.jpg.3511a5254972cb82c44108a131a77cfc.jpg

 

Thank you again for the awesome feedback!

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