spark plugs

[capt den]

yesterday i did a compression test on my 54 windsor. all cylinders on or about 95 psi. not great but it will do. the plugs were all very black and sooty, like fireplace soot. two of them were not firing at all. they are ngk br6s.before these i had AC 45 plugs.the motors manual lists autolite 4s140, which i am sure is an obsolete number. my guess is i need a hotter plug, but not sure what number if i go back to the AC plugs. the original plugs when i got the car were mopar plugs and they have a slightly longer electrode than the AC 45. i believe the black sooty plugs can be corrected with a hotter plug. am i right,or is this a carbeurator issue? or both? the cap,rotor and points are all fairly new. the car runs great.any advice is appreciated to know which plugs to but.    thanks,   capt den

[greg g]

Question is what the source of the soot is? You can treat the symptoms with hotter plugs, but should still look into the source.  Couple initial items is the choke butterfly opening fully at operating temp, is the step up jet getting its vacuum signal to keep it closed until needed, and are you using an eccessive amount of oil.  95 psi cold and dry is indicative of an old engine 8n pretty good condition.

[Tom Skinner]

Buy New Champion Plugs (592's/RJ12)) and throw out the others. Take it out on the Highway and blow stink off - as Grandpa used to say. LOL.

Now seriously use a Vacumm Gauge and Set the Timing and Carburator to the Highest Setting. Run it. smooching around at low speeds just adds to the soot.

Go run her at 55 - 60 for 20 miles, then come home and read your plugs. The more you drive these old Buses the happier they are.

Tom

[capt den]

thanks for the replies. i do not know alot about carbs, but i can check the choke butterfly. not sure what the step up jet is or how to check it. not burning alot of oil, but it does burn some. i do not have a vacuum guage, but i should buy one and learn how to hook it up. i used to use champions, but they were getting bad reviews from alot of people, so after trying ac i went to the NGK, but they have failed me. i never had issues with the champions. i was just wondering if a hotter plug will help with the soot issue. not sure what the autolite 4S140 is in todays plugs. someone here may know how to cross reference that number. as soon as i get new plugs i will take the old bus out for a drive like tom suggests.   thanks again    capt den 

[greg g]

 

 

This is from Wikipedia.  I don't know what carb the Chryslers used but the principle remains.  The valve is held closed by a vacuum passage that connects though the carb to the intake manifold. If the passage gets blocked the jets remain open causing an over rich mix all the time.  It also can lead to poor fuel economy.   If you are getting 10 mpg or lesss, this maybe the culprit.  Do you get Grey or black smoke out the tail pipe 9n start up or when reving up?  Hold up a piece of cardboard to your exhaust after the car is warmed up and have some one rev the engine a couple times.  What does the cardboard look like?

.

Power valveEdit

For open throttle operation, a richer fuel/air mixture will produce more power, prevent pre-ignition detonation, and keep the engine running cooler. This is usually addressed with a spring-loaded "power valve", which is held shut by engine vacuum. As the throttle valve opens up, the manifold vacuum decreases and the spring opens the valve to let more fuel into the main circuit. On two-stroke engines, the operation of the power valve is the reverse of normal — it is normally "on" and at a set rpm it is turned "off". It is activated at high rpm to extend the engine's rev range, capitalizing on a two-stroke's tendency to rev higher momentarily when the mixture is lean.

Alternately to employing a power valve, the carburetor may utilize a metering rod or step-up rod system to enrich the fuel mixture under high-demand conditions. Such systems were originated by Carter Carburetor^{[citation needed]} in the 1950s for the primary two venturis of their four-barrel carburetors, and step-up rods were widely used on most 1-, 2-, and 4-barrel Carter carburetors through the end of production in the 1980s. The step-up rods are tapered at the bottom end, which extends into the main metering jets. The tops of the rods are connected to a vacuum piston or a mechanical linkage which lifts the rods out of the main jets when the throttle is opened (mechanical linkage) or when manifold vacuum drops (vacuum piston). When the step-up rod is lowered into the main jet, it restricts the fuel flow. When the step-up rod is raised out of the jet, more fuel can flow through it. In this manner, the amount of fuel delivered is tailored to the transient demands of the engine. Some 4-barrel carburetors use metering rods only on the primary two venturis, but some use them on both primary and secondary circuits, as in the Rochester Quadrajet.

[kencombs]

20 hours ago, Tom Skinner said:

Buy New Champion Plugs (592's/RJ12)) and throw out the others. Take it out on the Highway and blow stink off - as Grandpa used to say. LOL.

Now seriously use a Vacumm Gauge and Set the Timing and Carburator to the Highest Setting. Run it. smooching around at low speeds just adds to the soot.

Go run her at 55 - 60 for 20 miles, then come home and read your plugs. The more you drive these old Buses the happier they are.

Tom

Not disagreeing, because I've never  had a Champion problem, but you're the first person that I have seen recommend them in years.  most complain about them and suggest NGK.    After putting in new plugs of choice, run at highway speed for a few miles, minimize idle time, then pull the plugs and read their condition and color.  That should allow you to determine whether it is oil or rich mixture.  IMO, it is never the plugs at fault when sooty.

Edited August 30, 2021 by kencombs

[kencombs]

3 hours ago, capt den said:

thanks for the replies. i do not know alot about carbs, but i can check the choke butterfly. not sure what the step up jet is or how to check it. not burning alot of oil, but it does burn some. i do not have a vacuum guage, but i should buy one and learn how to hook it up. i used to use champions, but they were getting bad reviews from alot of people, so after trying ac i went to the NGK, but they have failed me. i never had issues with the champions. i was just wondering if a hotter plug will help with the soot issue. not sure what the autolite 4S140 is in todays plugs. someone here may know how to cross reference that number. as soon as i get new plugs i will take the old bus out for a drive like tom suggests.   thanks again    capt den 

One fairly common issue is the gasket between the manifold and carb.  There is a vacuum passage in it that allows manifold vacuum to reach the step up piston or power valve.  The wrong gasket or improperly installed one will block that and cause it to be very rich, all the time.   If the issue started after the carb was removed and replaced that is a possibility.  Or the vacuum piston may just be stuck.

[9 foot box]

   A br6s crosses to an Autolite 303. That’s a cold plug. I run non-resistor Autolite 295 that crosses to an AC45 or 46 being slightly hotter or an NGK b4. I think NGK uses 3210 as the new number. So my suggestion would be clean and gap your old AC45’s, and check them after a run. If still not burning clean, go to Autolite 306, NGK b4, or Champion 511. Resistor plug gap set at .035”, non-resistor at .028”. This all assumes you have solid core and not carbon core wires and all wires firmly seat in the distributor cap. I solder the distributor ends of all the wires. You can check the continuity of each wire with a ohm meter.

[capt den]

i will try AC46. i never had trouble with AC plugs. i could have a gasket issue with the carb. can i get just the carb/manifold gasket somewhere. and yes, i sometimes get grey smoke on startup. mileage is poor but i will have to check it. it will only get 15 at best, but it is lower than that now. i have a local guy who does a very good rebuild, but it costs about 300 for the one barrel. i have been thinking about getting it done. i will put new plugs in and check some of the other suggestions, even the cardboard test. i assume it should not look black/sooty when the test is done.   thanks,   capt den

[Sniper]

$300 for just a rebuild on a supplied 1bbl seems excessive.  I assume that does not include bushing the throttle shafts or anything beyond, disassembly, cleaning, inspection and reassembly.  The kit is well under $50 and it takes maybe 2 hours to do it right, assuming it's not seriously plugged up with goo and needs additional soaking time.   

[capt den]

not sure about all that is included. i had one done about ten years ago by this guy and he told me he checks it out on some kind of flow machine so the carb is up to all factory specs.the one he did really made the car run better so at least i felt like i got a good if not costly product. not sure if i want to spend that kind of money now if it is not really needed.    capt den

[capt den]

i put autolite 306 plugs in. you can see a little soot in the exhaust and my mileage has gone south. guess i need carb work.   capt den

[capt den]

this car had mopar spark plugs #4091936 when i bought it in 2006. these are still available, but they are not listed as compatible with a 54 windsor. not sure if i should go back to them. seems like champion makes them. too confusing.    capt den