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Flathead 6 not starting in colder weather Plymouth & Desoto

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I am asking this to try and help my neighbor.

 

He has a '49 Plymouth and '51 Desoto. I changed oil for him back in October and used 40w oil since the cars were both using oil and it was recommended I try a heavier oil.

 

Now that the temps are down in the 30/40 degree range in MN the cars will not start. They both turn over fine on the 6 volt system.

 

The Desoto doesn't seem to fire at all, but I can see gas at the carb base and the choke is working. 

 

The Plymouth did try firing a couple of times, but wouldn't actually start. It was a little difficult to start back in October, but would eventually start with enough pumping of the accelerator. 

 

Both cars have been running and starting very well until now. 

 

I suspect a weak spark. My '49 Plymouth is 12 volt and starts very well even in the colder weather. My '52 Mercury is 6 volt, but started right up when I wanted to drive it last weekend after sitting for quite some time. 

 

How can I try to help him out?

 

Thanks! 

 

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13 minutes ago, greg g said:

What do the spark plugs look like??  If all they were driven was short trips, they may need cleaning or replacing. To fire when it's cooler.  Chokes working properly?

 

I will need to check the spark plugs - I didn't dig that far in last weekend. The choke seems to be working properly on the Desoto - it was closed when I removed the air cleaner to check. I will have to check this on the Plymouth. 

 

Thanks for the suggestions. 

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After the normal tuneup things, I'd check the voltage at the coil while cranking.  It's possible that the heavy oil increases the current draw to the  point that the power left for ignition is marginal.

 

Heavy oil may help the oil burning, but IMHO 15w40 would be a much better choice.  15 for cold start and 40 when at operating temp.

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If one or both cars have the electric chokes on them check to see if they close to 100% before trying start and just a little throttle, then open about 20%? while cranking over.

 

That is proper operation. They will slowly open with heat as motor runs and a least a little throttle.

 

Just one more thing that is least easy to check after air filter removal.

 

DJ

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Multi-weight, detergent oil is good, however only after the old sludge has been cleaned out. 

Cold air does cause different issues. It is denser and therefor more fuel helps richen the air/fuel mixture. 
 

Another problem is when fuel is pumped into the carb venturi it  creates a nice fine mist. You can see it. It appears like a fog around the throttle valve if you look down the carb throat. When this fog hit the sides of the cold manifold, head and cylinder it condenses again. Collecting as tiny droplets on the walls of the cold metal parts.  These droplets don’t want to ignite and combust. 

Add to that, a weaker battery, even if its 100% charged. The cold weather robs cranking amps.  Add some questionable spark plugs. Perhaps lower compression in an old engine. Factor in thicker weight oil. It all adds up and takes a toll.  
 

 

 

Edited by keithb7

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I used to fool some of my cars into thinking it was warmer out.  Put 75 or 100 watt bulbs in my trouble lights, then put one next to the battery and the other under the carb float bowl resting on the intake manifold.  Would get up in the morning and see that if it had snowed during the night, it would not be on the hood over the bulbs.  Cars would always start right up.  However getting 100 watt incandescent lights these days is next to impossible and their modern equivalents don't produce 1/3 the heat.

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1 hour ago, DJ194950 said:

If one or both cars have the electric chokes on them check to see if they close to 100% before trying start and just a little throttle, then open about 20%? while cranking over.

 

That is proper operation. They will slowly open with heat as motor runs and a least a little throttle.

 

Just one more thing that is least easy to check after air filter removal.

 

DJ

 

They are both electric chokes. I'll have to check this. I kind of wish the manual chokes would have been left on these cars even though the technology was supposed to have been improved. 

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I just tuned up the Cambridge this weekend.  there are a couple of things that are different due to temperature concerns.  Off the top of my head since I am about 5 hours from home till Friday they are as follows.

 

Oil viscosity, both in the crankcase and oil bath air cleaner, is thinner.

Accelerator pump shot is different, more so as to compensate for the condensing issue someone mentioned.

 

On my 51 the fast idle speed is not adjustable and I don't believe it is on either of yours.  But if it is, check that.  Wouldn't hurt to just tune it up altogether.

 

 

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Yesterday when I was a kid in high school, I had a 51 ford truck with a flathead v8. In winter time I had to toss a rag over the carb to get it to start.

Yes the manual choke worked, the engine was rebuilt and ran great and started fine in warmer weather.

I did need to remove the air cleaner in winter to put a rag over the carb.

 

Looking back at it today, I think the carb was probably wore out, using the rag it did give it a richer start, to much air sucking in around the choke plate.

Just a idea to try, you know if it does start easier with a rag over the top of the carb, it will give you a starting point for troubleshooting.

 

Back then (yesterday) when I was 16, I was pretty quick at starting the truck and then run around to the front and pull the rag off the carb before it choked out and died.

Little slower today.

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6 hours ago, greg g said:

I used to fool some of my cars into thinking it was warmer out.  Put 75 or 100 watt bulbs in my trouble lights, then put one next to the battery and the other under the carb float bowl resting on the intake manifold.  Would get up in the morning and see that if it had snowed during the night, it would not be on the hood over the bulbs.  Cars would always start right up.  However getting 100 watt incandescent lights these days is next to impossible and their modern equivalents don't produce 1/3 the heat.

Not to hijack the thread too far I just checked on Amazon and rough service incandescent 100 watt bulbs are still available. I bought some a few years ago and was informed that that type was not among the banned and dreaded regular incandescent ones. My Father did the same thing. Wouldn't buy a new battery no matter what.  Waste of money he would say.

Edited by plymouthcranbrook

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Seems to be more of a tuning and maintenance issue and not weather. If the plymouth was starting hard when the weather was warmer, has to be a fuel or ignition or both. Start with the basics.

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Doing a little research here in my 1942 Dyke’s Encyclopedia I read this. Just to help pass along a little bit of info. 

 

 

 

1B452C06-0BC6-40DF-8284-BE8FFBD19AA3.jpeg

Edited by keithb7

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Which is why intake manifold and or incoming air is warmed by heat risers or exhaust manifold stoves for intake air. During cold weather operations.  My owners manual says to pull the choke fully closed press the gas pedal to the floor to set the high idle cam, then crank the starter with the gas pedal pressed down about 1/3 of it's travel.  When in engines starts the choke should be opened and the throttle set to achieve a good smooth

warm up idle speed. This for my 46 P 15.

 

I would I stall fresh properly gapped spark plugs before or anything else.

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The systems to assist cold weather starting and quick warm up for smooth running engines, worked very well considering it was mastered so long ago. If maintained and adjusted properly. 

 

My ‘53 has a bi-metallic thermo spring style choke. It also has the high idle cam that keeps the engine rpms up for quicker engine warm up. It stays at higher rpms until I manually kick the gas pedal down once, blipping it. Then it idles nicely again.  Hot air from the exhaust manifold is pipe’d to the encased, bi-metallic coiled choke spring. As the spring gets warmer it’s length gets longer, casually and slowly opening the choke plate again.  Works great still!

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Back when, in the ‘50’’s , western Nebraska ranch, feeding cattle started every day. Tractors had to start!  Warm battery, warm oil. Dipstick heater worked fine and light weight oil. The effect of cold Wester on gasoline is interesting. In Omaha in the late ‘60’s my school cars were VW’s, had three of them. Even at 20 below, they always started. 

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You might also check the timing. If it is set to fire before TDC, colder weather makes it harder. Even in northwest Fl, it makes a difference during the 3 weeks of winter we get here.

 

Joe Lee 

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Wow! Three weeks of winter...I am so jealous☹

Not here in the Great Northwest

Three months of winter.

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Are the cars sitting for a couple weeks or more before starting?.

Possible fuel evap and drain back.

To help that..

Crank the engine for 30 seconds..stop cranking.....wait 5-10 minutes....crank again while pumping the gas pedal 5-10 times..

Engine should fire.

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Have you checked the position of the rod on the accelerator pump linkage? Might be in the center (standard) position....and starting may benefit from a change to the longer stroke winter position. I think it is worth a try.

Jeff

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