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1941 Flathead slow starting after warmup

Started by J. Russo, May 22, 2023, 10:57:32 AM

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J. Russo

When I first start my 1941 Cadillac with a cold engine, I press and release the fuel pedal as instructed and it starts as soon as I press the start button. No hesitation at all.

I'll drive the car for a while, say 30 miles, and turn off the ignition. I then let the car sit for about an hour before restarting. When I try to restart the engine, it turns over very slowly and I have to keep the pedal pressed in order for it to start. I then can smell the fuel pretty strongly at that point until it runs about a minute or less.

The carburetor and fuel pump have both been rebuilt to run on today's fuel. I run 87 octane regular unleaded.

The engine idles at about 400 RPM and runs beautifully.

Any suggestions why the slow starting would occur under this scenario is greatly appreciated.
Thanks,
John Russo
CLC Member #32828

Carfreak

Enjoy life - it has an expiration date.

J. Russo

Quote from: Carfreak on May 22, 2023, 12:22:22 PMWas just thinking about the late great Doug Houston last week. 

https://forums.cadillaclasalleclub.org/index.php?topic=122101.msg217542#msg217542

I'm sure this is a great idea, but my engine starts right up when it's cold. If I had a starting problem related to grounding or the battery, wouldn't it be slow to start all the time?
Thanks,
John Russo
CLC Member #32828

Mike Baillargeon #15848

Quote from: Carfreak on May 22, 2023, 12:22:22 PMWas just thinking about the late great Doug Houston last week. 

https://forums.cadillaclasalleclub.org/index.php?topic=122101.msg217542#msg217542

Is there a way to get back to that Doug Houston article in the Self Starter about that grounding stud on the starter?....

Mike
Mike
Baillargeon
#15848

LaSalle5019

#4
My 1939 LaSalle starts the same way with "0" size wiring and a rebuilt and grounded starter.

The problem is that with all the underhood heat the fuel boils out of the carburetor and dumps into the intake manifold. Additionally, the starter gets pretty hot and losses efficiency.

I've tried various things to improve hot weather performance but I think today's fuels are just a bit more volatile.

I have the anti-percolation valves set properly, it has the carb base insulator, a rear crossover heat shield and insulated fuel line - none of it matters.
IMG_5120.jpegIMG_5122.jpegIMG_5121.jpeg   

Carfreak

Below are a few previous forum topics discussing flathead starting, the suggested grounding stud, etc. There might be some pics included too. 

For more discussions on this topic, do a search on 'Grounding Stud' and you will find many.

If still needed, I could probably find Doug's article in the Self Starter in our Barn Archives. 

https://forums.cadillaclasalleclub.org/index.php?topic=120807.msg211043#msg211043

https://forums.cadillaclasalleclub.org/index.php?topic=94369.msg360120#msg360120

https://forums.cadillaclasalleclub.org/index.php?topic=99244.msg102803#msg102803

https://forums.cadillaclasalleclub.org/index.php?topic=151258.msg403167#msg403167

https://forums.cadillaclasalleclub.org/index.php?topic=65239.msg65439#msg65439
Enjoy life - it has an expiration date.

Jay Friedman

Art Gardner and I wrote a step by step article in the Self Starter several years ago explaining how to install an additional grounding bolt on the commutator end plate of 36-52 Cads and Lasalles following the Doug Houston method. I don't know how to post it to this forum, but if you email me at jaysfriedman(at)yahoo.com I can send by reply email. 

My '49 used to have the same problem with slow starting when warm. After installing the grounding bolt the problems was cured.  Art did it on his car, too, with similar results.
1949 Cadillac 6107 Club Coupe
1932 Ford V8 Phaeton (restored, not a rod).  Sold
Decatur, Georgia
CLC # 3210, since 1984
"If it won't work, get a bigger hammer."

LaSalle5019

Quote from: Jay Friedman on May 22, 2023, 02:38:30 PMArt Gardner and I wrote a step by step article in the Self Starter several years ago explaining how to install an additional grounding bolt on the commutator end plate of 36-52 Cads and Lasalles following the Doug Houston method. I don't know how to post it to this forum, but if you email me at jaysfriedman(at)yahoo.com I can send by reply email. 

My '49 used to have the same problem with slow starting when warm. After installing the grounding bolt the problems was cured.  Art did it on his car, too, with similar results.

It's in the July 2015 issue of the Self Starter. If you are a CLC member you have access to the back issues digitally. Here is the link starting on page 29

https://ssonline.cadillaclasalleclub.org/CLC_The_Self-Starter_2015-07/mobile/

RonMorey

John, this doesn't explain the slow cranking but are you sure there isnt vapor lock causing the gas smell and long cranking time?

J. Russo

Quote from: RonMorey on May 22, 2023, 06:44:06 PMJohn, this doesn't explain the slow cranking but are you sure there isnt vapor lock causing the gas smell and long cranking time?

I honestly don't know how to diagnose a vapor lock. The engine WILL start if I hold down the pedal while cranking/starting.
Thanks,
John Russo
CLC Member #32828

LaSalle5019

John,
Do you have an electric boost pump? I would be lost without mine.

I have just a slightly slower crank speed when hot. My issue is long crank due to fuel/air mixture issues.
Scott

J. Russo

Quote from: LaSalle5019 on May 22, 2023, 09:39:54 PMJohn,
Do you have an electric boost pump? I would be lost without mine.

I have just a slightly slower crank speed when hot. My issue is long crank due to fuel/air mixture issues.
Scott

I don't know what an electric boost pump is.
Thanks,
John Russo
CLC Member #32828

LaSalle5019

Well, that makes a huge difference in these cars. Like many, I have an Airtex 6 volt electric boost pump added nearer the fuel tank in the fuel line. This allows you to fill the float bowl after a hot soak and also to compress any fuel vapor in the lines back to a liquid. My 1939 LaSalle has horrible front end airflow and is really prone to vapor lock. I have an under dash switch that I momentarily run the pump with prior to cranking.

I only run it for starts, not for driving down the road. It will greatly reduce long cranks.

z3skybolt

#13
I am of no help but want to tell of my experience with two different 1940 LaSalle.  My first one behaved exactly as described above.  Started easily when cold and would nearly run the battery down during hot starts. Had to use the electric pump always when starting hot.  It vapor locked all the time.  Hot weather or cold made no differnence. It never ran more than 10 miles without having to use the electric pump to keep it running. This was a perfectly tuned engine including a $12,000.00 overhaul.

Forward to my current LaSalle.  No electric fuel pump.  Never vapor locks. Starts instantly hot or cold!!  I have owned it two years and driven it 4,000 miles.  The engine has about 8,000 miles on a professional overhaul. Nothing other than standard factory items under the hood.

Count me mystified.  I have no idea why either of my LaSalle behaves/behaved as they did/do. Both ran cool and never overheated. I tried all the tricks, suggested on this forum, with the first one. No benefit.  Pure serendipity with my second one.

Just pointing out.....these Flatheads can be mysterious.

P.S.  I run 91 octane non-ethanol gasoline with a few oz. of Marvel Mystery Oil added to each tank fuel.  Same fuel with both of the cars.

Good luck with yours,

Bob R.
1940 LaSalle 5227 Coupe(purchased May 2016)
1985 Lincoln Town Car Signature Series. Bought New.

LaSalle5019

Quote from: z3skybolt on May 23, 2023, 10:06:30 PMI am of no help but want to tell of my experience with two different 1940 LaSalle.  My first one behaved exactly as described above.  Started easily when cold and would nearly run the battery down during hot starts. Had to use the electric pump always when starting hot.  It vapor locked all the time.  Hot weather or cold made no differnence. It never ran more than 10 miles without having to use the electric pump to keep it running. This was a perfectly tuned engine including a $12,000.00 overhaul.

Forward to my current LaSalle.  No electric fuel pump.  Never vapor locks. Starts instantly hot or cold!!  I have owned it two years and driven it 4,000 miles.  The engine has about 8,000 miles on a professional overhaul. Nothing other than standard factory items under the hood.

Count me mystified.  I have no idea why either of my LaSalle behaves/behaved as they did/do. Both ran cool and never overheated. I tried all the tricks, suggested on this forum, with the first one. No benefit.  Pure serendipity with my second one.

Just pointing out.....these Flatheads can be mysterious.

P.S.  I run 91 octane non-ethanol gasoline with a few oz. of Marvel Mystery Oil added to each tank fuel.  Same fuel with both of the cars.

Good luck with yours,

Bob R.

I'm jealous. One thing I wonder is if I put a check valve parallel with the pump if that would help. I guess I could just bypass the pump and see if it makes a difference. The thought being....if the pump causes a slight restriction to the pump, that would decrease the pressure (increase vacuum) on the tank side of the mechanical pump which would cause the fuel to boil more readily. Maybe worth a try.


harvey b

Have you checked the engine timing.if the timing is not exact,these cars will be hard to start when warmed up.they may seem to run better if advanced a bit but it will affect the warm startups.I would try that first. harveyb
Harvey Bowness

J. Russo

Quote from: harvey b on May 25, 2023, 08:31:35 AMHave you checked the engine timing.if the timing is not exact,these cars will be hard to start when warmed up.they may seem to run better if advanced a bit but it will affect the warm startups.I would try that first. harveyb

Yes. The timing has been verified.
Thanks,
John Russo
CLC Member #32828

Jeff Hansen

John,

Make sure ALL of your electrical connections in the starting circuit are CLEAN and rust free.  This includes where the starter solenoid contacts the starter motor and where the starter motor contacts the block.  It also goes without saying to make sure your battery cables are properly sized.

Hope this helps,
Jeff
Jeff Hansen
1941 6019S Sixty Special
1942 7533 Imperial Sedan

Tom Boehm

Jeff Hansen, does a hot engine increase the electrical resistance in dirty connections? Why do they crank slower when hot?

Jay Friedman

#19
Quote from: Tom Boehm on May 25, 2023, 08:47:14 PMJeff Hansen, does a hot engine increase the electrical resistance in dirty connections? Why do they crank slower when hot?

In my opinion, what is happening is that a motor starts easily when cold because the piston clearances are "normal". When you drive, particularly at higher speeds, the motor gets hot and then the ignition" is turned off, the coolant is no longer circulating. In this situation the pistons as well as other parts get very hot and then expand. This expansion causes the piston clearances to decrease, creating a greater amount of friction which causes the starter motor to turn more slowly. With only 6 volts and with possible dirty grounding points it doesn't take much extra load to cause this to happen. After a while, when the motor cools down, the car will start normally. 
1949 Cadillac 6107 Club Coupe
1932 Ford V8 Phaeton (restored, not a rod).  Sold
Decatur, Georgia
CLC # 3210, since 1984
"If it won't work, get a bigger hammer."