Won't Rev 2.0

[DonaldSmith]

Per the "Won't Rev" thread, which should be allowed to rest in peace, the car would only rev so fast in 3rd, but could keep up with traffic in 4th.  I rebuilt the carburetor to "rule out" carburetor issues.  Oh, the car runs sweet at lower revs.  And I developed great skills which I may never have to use, but I can tell people about.

 

I took a more extensive drive this morning.  Starting in 3rd, it goes well until it approaches 25.  Then it stays at that speed, no matter how far I push the pedal.  On Woodward, I could upshift at 25 and get the speed up to 45, maybe 50.  I could keep up with the bus in front of me, but no better.   At the top revs, the engine is not running smooth.  I don't want to find out what an extensive run in that condition would do. 

 

I followed the carb rebuild instructions religiously.  Did I miss something?  High speed jet?  I sprayed it and blew it out.  I didn't try to remove it.  Does it have a miniscule opening that should have been cleaned out with a fine wire?  It is accessible from the bottom of the carburetor,. so I wouldn't have to take the carb apart.  Any high-speed-jet gurus out there?  

 

If I can "rule out" the carb, I'll turn to ignition.  I made a propitious offering to the gods, and bought an Echlin coil.   I had left the Pertronix coil in place when I went back to points; maybe it resents the change.  (I'll reset the plugs to 0.035 instead of 0.040 when I change the coil.)   I had put a new condenser in, with the new points.  Will I be playing the condenser game?  Suggestions accepted graciously. 

 

I can try something, and take a drive.  At least a short drive would tell the tale.  I should be able to floor it in 3rd and get it up well past 25.  Stay tuned.   

[nonstop]

I would suggest doing the coil, then condenser.  Have had bad (cracked) Pertronix coils out of the box.  I am not necessarily a fan of Pertronix, but am still running one in my Royal.

 

I have also had condensers fail (multiple different brands) almost right away.  I now carry a few spares.  
 

Both the coil and condenser are very viable culprits.  Might as well check the wiring while you’re in there too.

[DonaldSmith]

I sent a message to Mike's Carb, asking if there is anything in the high speed circuit that I might have missed in rebuilding the carb. 

Meantime. I turned my attention to the mysteries of the ignition system.  I installed a new coil, Echlin, via NAPA auto parts. 

 

Then a bonehead play.  The plugs for the Pertronix were gapped at 0.035.  I thought I had better re-gap the plugs back to 0.030. 

Working too hard.  I had replaced the plugs when I went back to points. They were already 0.030.  I gapped them to 0.035.  The car didn't like it. 

I think I'll re-gap them to 0.030, and clean off the soot. 

 

Meanwhile, I'm wondering if the centrifugal advance might not be working right.  Is it possible, that ancient alien astronauts . . . . (different show)

Is it possible, that there is something wrong with the centrifugal advance system that's affecting the timing at high speeds?   

[kencombs]

Not likely, but it's easy to see with a timing light.   Should advance per specs with minimal drifting at set speeds.  One thought since you're now using points.  Examine the spring.  Lots of reports of springs not closing them consistently, sometimes because the spring and conducting strap are separate and not both captured under the nut.  

 

But that should also be visible with a timing light.   Missing ignition events at speed.   IOW, light doesn't flash consistently with the rpm associated with your running issue.

[FarmerJon]

Are you currently running points or Pertronix?

 

If points, check your condenser with a multimeter. 

 

If running Pertronix,  swap your points back in and test.

 

If the problem is the same with both then you can move on.

 

 

Pulling the distributor out and apart is fairly easy. Cleaning and lubing the advance weights wouldn't hurt. Check that the points plate can move free and smooth. Check that your vacuum canister is not leaking air.

Check points gap on all 6 lobes. 

Check that the wires inside are not shorting out and are attached tightly. 

 

What is your base timing set at?

 

Outside of ignition, 

Are your valves recently adjusted? 

Does the engine have a good ground?

 

Unrelated,  what transmission do you have with a 4th gear, that you start off in 3rd?

 

[DonaldSmith]

Thanks, FarmerJon.  You get the "solution" nod, for your ignition check list  and the video on checking condensers. .

 

No one ever told me how to check a condenser with a multimeter.  No more crap shoot, if we know the relative health of the condensers. 

 

(My transmission is Ma Mopar's M5, postwar semi-automatic, with the fluid coupling.  Typically, start in the High range (3rd gear) and "accumulate momentum".  At some point, let off the gas, and the transmission will upshift to 4th.

 

The video showing the capacitor testing is for a negative ground system.  I would discharge the condenser first, using the DC voltage feature of the meter. 

The man in the video charges the condenser by setting the meter to mega ohms, (2000k ohms on my meter).  This uses the meter's battery to send voltage through the object being tested.   He connects the (-) lead to the condenser body and (+) lead to the end of the lead wire.  

Meter on, and it charges the capacitor until it can take no more.  (My meter reads "1" in that case,) Keep the meter connected for maybe 30 seconds, to make sure the condenser fully charged. 

Switch the meter to DC volts, with 3 spaces to the right of the decimal point.  Connect the meter and take a reading of the condenser voltage.  The number should be dropping.  Disconnect the meter and remember what the last number was. Wait a couple seconds, and reconnect again.  The first number should be close to the remembered number.  Repeat until the number approaches zero. 

 

A good condenser will readily accumulate voltage and will store it for a reasonable time.  I would have to play with a number of condensers to see what sort of range I ge, to judge the relative health.        

 

 

[Ivan_B]

Did you actually resolve the issue buy adjusting the ignition? I was going to suggest checking the fuel\air supply, in this case

[Sam Buchanan]

Are you sure there are no restrictions in the muffler or air filter?

Edited July 5, 2023 by Sam Buchanan

[Ivan_B]

Huh, even simpler: I would first verify that the throttle opens all the way. Seen this one a few years ago. Idle reved fine, but in motion the car could not get up to speed. Turned out that the pedal linkage was not properly adjusted, and the pedal to the floor was only opening the throttle about 1/3 (forget about the accelerator pump). Good on gas mileage, I guess ?

[DonaldSmith]

More things to check. 

Gap the plugs right, to get back to where it was running smoothly at low speeds. 

Check the throttle plate for full opening.  That would be a quickie.  (Also the automatic choke linkage.  It bit me before.)

Check the muffler and tail pipe for obstruction? I could use a suggestion on how to do that. 

 

Check the carburetor for blocked passages (Per Mike's carbs).  (I just noticed that the air horn has a cast-in passage from the main jet to the brass tube that sticks up into the air flow.)  Take another look at the step-up piston.  (James Douglas said something sometime ago about the piston getting stuck, and what that would do.)

 

Then go to ignition? 

 

[Sniper]

Capacitance meters are cheap and give you a specific value.  Using a multimeter like in the video is just a quick and dirty check that doesn't tell you the capacitance value, so it could drift on you  and still pass the MM test shown.

 

About .25uf (microfarad) is what you want.

Edited July 5, 2023 by Sniper

[DonaldSmith]

I could pop for a capacitance meter, but that's another level of sophistication. 

For these cars, what capacitance values are we looking for? 

Shouldn't a NAPA condenser out of the box meet whatever capacitance is required?  Or they go bad on the shelf? 

Horror stories abound.  

[Sniper]

Electrolytic capacitors, which is what a condenser is, do dry out over time.  So NOS is not necessarily a guarantee.  The capacitance meters start at about $25, not too steep a price

 

https://www.amazon.com/Honeytek-Capacitance-Capacitor-Electronic-Measuring/dp/B08LYM533X/ref=sr_1_2_sspa?keywords=capacitor+tester&qid=1688595648&sr=8-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1

[Plymouthy Adams]

while the spec is not in the book specifically the value is typically in the .18 to .27 uF for many condensers......if it is any help the book does call for .25uF for a 1961 slant 6...

 

 

[Sniper]

There is a method to determine the correct value for your specific setup, basically it depends on where the points deposits end up. 

[Ivan_B]

So, the problem was not resolved, yet? If the car does not rev/get to the proper speed (especially uphill), the ignition is the last thing I would check.

Check how it works without the air filter - same?

Check the throttle opening - all good?

Does your carb have an accelerator pump? If it does, looking into the throttle, you should see a fuel squirt when someone presses the gas pedal good enough.

 

For the exhaust - no idea how to check it properly, but you could probably take the plugs out, and connect a vacuum cleaner to the tailpipe to see if you get a good suction at any of the cylinders

[Jerry Roberts]

Looking in a Motor's Truck and Tractor Repair Manual that covers years 1936 - 1947 ;  Auto-Lite condenser capacity varies from .23-.26 , .25 - .28 , .20 - .25 

[desoto1939]

I have a condenser testing machine. When i test some of my older Autolite condensers to the unit I get readings higher that what you have stated above and get readings into the 3-4 range.

 

So are my OLD stock condensers bad or are they ok.

 

Rich Hartung

[Plymouthy Adams]

first, ensure your tester is up to the task and not with issues due to older components in its construction or losses/gains in test leads and connections.....comparing your older unit with a newer unit that is so commonly available or perhaps one owned by a friend will go a long way in the trust department.   Without some known standards to bounce across your is likely just a guess.  

[Jerry Roberts]

1 hour ago, Jerry Roberts said:

Looking in a Motor's Truck and Tractor Repair Manual that covers years 1936 - 1947 ;  Auto-Lite condenser capacity varies from .23-.26 , .25 - .28 , .20 - .25 

I found the Mfd's for the 1940 - 1954 De Sotos in another Motor's manual ;  .25 - .28  

[desoto1939]

Here is a picture of my Hills Condenser tester: Found this on Ebay around $25 if I remember correctly.

Second set of pictures shows a 50 year old Autolite Condenser being tested and a reading of .4 MF versus a newer condenser reading a .2MF

the third picture is a generic picture of most used condensers and is used to show the differences. Basically they are all the same, the main difference if how they are attached to the dizzy, the length of the wire the type of clip or ring at the end and which direction the wire comes out of the main body of the condenser.

 

This information was taken from my power point presentation on Condensers and the use of the Condenser tester.  After buying NOS Autolite condensers for my 39 Desoto I always test them to get the mf reading and then prior to installing in the dizzy i retest them.

Just a nice tool to have when you need it.

 

Rich Hartung  Desoto1939@aol.com

 

 

 

[Plymouthy Adams]

2 hours ago, desoto1939 said:

I have a condenser testing machine. When i test some of my older Autolite condensers to the unit I get readings higher that what you have stated above and get readings into the 3-4 range.

 

So are my OLD stock condensers bad or are they ok.

 

Rich Hartung

 

 

I see you have now successfully placed the decimal point.....

[FarmerJon]

@DonaldSmith Any progress? 

[desoto1939]

On 7/6/2023 at 5:53 PM, Plymouthy Adams said:

 

 

I see you have now successfully placed the decimal point.....

 

Figured everyone would know that there would be a point before each number based on the pictures of the condenser testing unit.

 

Rich Hartung

[Plymouthy Adams]

when troubleshooting or stating values.....that decimal points screams trouble loud and clear...goes a long way in establishing the truth eliminating any confusion with readers...maybe others assumed, maybe they did not know....but with older equipment, older leads and connections messing with used components....remove the assumptions and guessing.