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1939 Chrysler Royal Misfire


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I have a misfire on my 1939 Chrysler Royal 6 Cylinder after it warms up for about 5 minutes. I've tuned it up, had the carb rebuilt by All American Carb, installed a new fuel pump, and new plug wires, The engine starts fine and runs great until it warms up. What would cause this? I hate to start replacing parts and waste what little money I have. The vacuum gauge reads fairly steady at 17 and when misfires drops to 16. I've advanced the timing slightly to because of the low reading on the vacuum gauge.

 

As a side note - the rebuild by All American Carb was outstanding. I had a local carb shop in NY rebuild the carb and wasn't satisfied with their work. The local rebuild made the car run rough and decided to find another shop that could do the job right. I read some posts here on the forum about All American Carb in FL and the comments were spot on. Their rebuild made the carb look and perform like brand new.

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Can't help with misfire issue, but thought Chrysler Royal fans might enjoy seeing a picture of my Dad's '37 Chrysler Royal taken in about 1945/46, around the time I was born. Seems he got stuck in the mud on a Sunday drive, and was using all means possible to get unstuck. Jack seems to be helping along with a shovel. I'm sure the air was blue that day. Don't know what to say about that "upside down" bumper from another car, 

WillardandCarcirca1945.jpg

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You could try shorting the plugs out or pulling the plug leads one at a time to find out which cylinder is missing. Be careful you don't get a lifter, use an insulated pliers or pull the wires from the dist cap.

 

How do the plugs look? Have you done a compression test? Valve adjustment might fix it, if a valve is too tight.

 

It's awfully hard to diagnose a vague complaint like this from a thousand miles away. Maybe all your car needs is a shot of Marvel Mystery Oil in the gas and 100 mile blast up the highway.

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I replaced the condenser with the tune kit and nothing changed, I'll try adjusting the valves first. What is the best way to adjust them cold? I was told to adjust them 2 one thousand inches over cold (so I don't burn my arms / hands on the exhaust). Do I just turn the car over with the starter a little at a time by myself until I get all the valves adjusted? I hope the coil isn't crapping out because that costs some serious coin. I changed the plugs (oily old ones) and the dry compression tests were all great and very close (120 lbs).

Edited by Doug 845
missed word (see edit history)
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I adjusted the valves cold - 2 thousands over @ .010 & .012 by turning the car over with the distributor cap off. I could see when the rotor was at the high point of the cam at each cylinder and then traced the wires back to each spark plug and adjusted each pair of valves individually. I found that the #4 intake valve was way to tight and the #3 exhaust valve was slightly lose. I then started the car and let it run for about 10 minutes and did the same tracing procedure and checked the hot factory clearance specs of .008 & .010. I was surprised to see that the valves were nearly perfectly set using the cold clearance settings. I had to only tweak a couple valve clearances. The car runs better and I adjusted the timing back to TDC. I still doesn't run perfect - but it did improve. I wondering if I set the valve gap slightly wider that the car would run even better after if warms up. Perhaps my expectations are a bit to high - expecting a 1939 car to run like a 2016 model. Thanks to all who replied to my posting.

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It only takes a few minutes to try a different point adjustment, so may be worth the test.

Be aware that adjusting the points will affect the timing, however adjusting the timing will not affect the dwell (points adjustment)

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Please don't be insulted, but I suggest that you confirm the sequence of plug wires you replaced, comparing the firing order in the cap with that of the factory specification which is usually cast into the head or intake manifold.  I've screwed that up myself more than once, even after knowing better.  I've learned to use an ohmmeter on the two ends of each plug wire to confirm I have the right wire in cases where a loom or bundling of wires can confuse the issue.

 

And please check the actual dwell against the published (desired) dwell.  In a recent thread I recalled my experience many years ago with a Pontiac 6 with worn distributor cam lobes, in which I had to set the points at 0.014 (vs. published spec of 0.020) to get the correct dwell reading.  The actual DWELL is what makes the car run well, and the point gap is a mechanical expression of that but only while you have unworn cam lobes.

Edited by Grimy
add zeroes to correct point gap info :-) (see edit history)
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If it runs smooth to start with then it won't be plug wire sequence. I had a similar problem. Car ran very well until it reached operating temperature. Turned out to be the spark plugs. From your description I'd be looking at the coil or the plugs.

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A friend of mine afew weks ago tuned up his '59 Jaguar himself, including new plugs, wires, etc. Warmed car up, took it for a spin, got about 100 yards, car misfired and conked out. Would not start. Towed to the local European car specialist, who took 5 minutes to sort the problem. Owner had installed incorrectly rated spark plugs. Proper plugs were installed, car works perfectly. So, you may want to confirm the plugs are properly rated for your installation.

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I followed the shop manual and made sure the new wires are correctly installed. I installed new Autolite 306 spark plugs - gapped per manual specs. I ordered a replacement coil from Andy Bernbaum and will install that next weekend after I receive it. Based upon his advice I ordered the generic 6 volt coil and will have to make an adapter of some sort. He said he could get an original one made but it would take 4 weeks and cost $225. He said try the $39 coil first to make sure that the coil is the problem.

Jack M suggested checking the dwell which I will do first. I didn't realize that gap setting & dwell setting is the same thing. I do own a 6 volt dwell meter.

Grimy refers to worn distributor cam lobes which make perfect sense because I noticed this when I replaced the points. By using Jack M's & Grimy's suggestion, I will use the dwell meter to fine tune the dwell setting.

Thanks to all - I will post results after the dwell adjustment.

Edited by Doug 845 (see edit history)
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  • 1 month later...

I installed the new coil and it seems to have improved. The dwell meter I have is old and finicky. I have to play with the switches to get it to work. The best I could do was to get the dwell set at 22 instead of 20. The timing is correctly set at TDC. The only problem I have now is the carb. After the car engine is completely warmed up, the throttle plate opens wide open and the car starts to run rough. If I slightly close the plate the car runs smooth. Is the plate suppose to be wide open when warm or slightly closed?    

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If you are referring to the choke plate rather than the throttle plate; the choke plate should be completely open when the engine is warm.

 

Carburetor adjustment should be made AFTER the choke plate completely opens. Any partial closure of the choke plate will artificially enrichen the mixture. Because of this, the engine will run at a higher RPM until the choke completely opens.

 

Jon.

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Lean mixture = needs a little choke when warmed up, can also point to a vacuum leak. To check for a vacuum leak with the car running spray WD40 around the base of the carb and the intake manifold joints, anywhere air could leak into the intake. If the engine speeds up and smooths out you have found the leak.

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c49er,

 

The point gap is set at .020. The Dwell angle is reading about 22. I am using an old dwell meter I bought off of Ebay that has to be played with to get it to work.. How do I adjust the dwell to reach 38. I am obviously not a mechanic and could use all the help I can get.

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I did not get a manual with the meter. I think the meter has seen better days. What I did was check for a vacuum leak with a smoke test. I found out that the throttle shaft is leaking from excessive wear. I'll have to ship the carb back to All American Carb and have a bushing installed.

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Doug - virtually NONE of these carbs with the cast iron throttle body ever wear sufficiently to require bushings. Occasionally, a VERY high mileage unit will require a new throttle shaft (the shaft will wear long before the throttle body).

 

SOME CLEARANCE BETWEEN THE THROTTLE SHAFT AND THROTTLE BODY IS REQUIRED, otherwise the shaft would seize when hot.

 

Design tolerance was 0.004 ~ 0.006 inch from the factory. Wear of an additional 0.003 (to a maximum of 0.009) is OK. Easy to measure with a dial indicator.

 

How did you determine that the throttle body needs bushing?

 

Jon.

Edited by carbking (see edit history)
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I called the shop and explained what I found when I did the smoke test. He said that the throttle shaft would be hard to find and a bushing might be required. There is a little wiggle room on the shaft when I move it. The car is a low mileage vehicle (59K mile). The car dies when the choke plate opens fully even after I adjust the carb for more fuel. The only vacuum leak I found was at the throttle shaft.

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The "smoke" test or the "propane" test or the "WD-40" test WILL ALWAYS FAIL!!!!

 

Note my previous post on clearance. If there is no clearance, the "smoke" test will pass, but the throttle will lock up when hot. 0.006 inch is enough for a little "wiggle".

 

Lots of enthusiasts/hobbyists have dial indicators. Just find a friend who has one, and measure the clearance.

 

And if the throttle shaft is worn, and the throttle body is not worn, installing bushings will not change the symptoms.

 

Jon.

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I called All American Carb and explained my carb problem again. The mechanic who rebuilt the carb told me to adjust the idle set screw and enrich the fuel mixture. It worked. My car now idles when the choke plate is fully opened. The car now idles very very slightly a little uneven with the vacuum gauge reading between 16.5 to 17. I checked my dwell again and now my old dwell meter is reading 36. I readjusted my timing to TDC.

c49er mentioned in a previous post my dwell should be set at 38. My shop manual doesn't have a dwell setting for my '39 Chrysler 6 Cylinder. Is 38 the correct setting for my '39? If it is, should I reset my point gap for such a small difference?

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Per a 1946 MoToR manual, your 1939 Chrysler 6 should have a dwell angle (they call it "cam angle") of 38 degrees.  Other specs are plug gap 0.025, breaker gap 0.020, timing at TDC, tappet clearance (hot) 0.008 intake and 0.010 exhaust.

 

Suggest you check for a small vacuum leak which may be reducing your vacuum reading.

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A couple notes...

The car will run just fine using a feeler gauge with very slight drag through the contact points.... this if you question using a dwell meter.

Do a accurate point setting then permanently set the timing.

You should not to have to check timing again.

 

You probably have a vacuum leak as mentioned.

Edited by c49er
spelling (see edit history)
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I would like to thank everyone who gave me the solutions to my problem. I am trying to get the car running its best before I put it away for winter. All I have left to do now are the brake wheel cylinders and shoes.Its great to have a forum of Chrysler experts providing much needed advice to novice backyard mechanics like myself. Again, thanks to all.

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As previously noted (I think), the DWELL is what makes it run right.  The point gap is how you adjust the dwell, but if distributor cam lobes are worn, you may have to vary from the specified 0.020 gap to achieve the correct dwell. Don't forget a little --very little--cam lube to minimize wear of the points' rubbing block.

 

And if you have a 3-wire 12V dwell meter, you can power it from a loose 12V battery, either a car battery or a small sealed unit such as used for gate openers or as backup power for home alarm systems.  I use the latter for 12V GPS and move it from car to car as needed.

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