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Discussion Starter · #1 · (Edited)
I have a 51 Desoto I am trying to get running (flathead 6). We have taken the head off and we cleaned it all up as well as made sure the valves moved freely ant that they sat fairly well. I have compression of around 60 in all cylinders but the second which has 20lbs. I have a hot blue spark that goes through all spark plugs and my wires are in the correct order. We took the carbeurator apart and cleaned it out/ replaced gaskets. The engine is timed top dead center on the first cylinder with a timing light. We get some smoke out of the crank case breather but not pop or running from the cylinders! There is a slight back pressure through the carburetor caused by the second cylinder (we have tried to run it with and without the spark plug in it to try to eliminate that back pressure).I have no clue what to try next. Any input/ ideas/ or new information would be greatly appreciated. Thank You
 

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are you getting gas

I would remove the fuel line from the carb and see if gas is getting to the carburetor. Maybe the float operated needle valve is stuck closed?

I have no idea what cylinder pressure should be in a flat six except it should be consistent cylinder to cylinder.

Send us a picture when you get it going. :)
 

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I would remove the fuel line from the carb and see if gas is getting to the carburetor. Maybe the float operated needle valve is stuck closed?
Agree with beertracker. To run, a motor requires fuel, oxygen and a spark delivered at the right time. You have oxygen and a spark. Now, make sure you have fuel and the spark delivered at the right time.

I have no idea what cylinder pressure should be in a flat six except it should be consistent cylinder to cylinder.
Me either, but I would expect maybe 80 to 100 lbs and like you say, consistent cylinder to cylinder, within maybe 10% of each other.

.
 

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You need to find out what it has such low compression. its not going to run with compression that low. I don't know anything about that engine but basic checks with low compression would be valve adjustment, timing chain or gears, head gaskets, rings etc.

taking a quick peek I came across this.1951 De Soto 250 Inline Six Engine Specs
Lots of info
 

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My book only goes to 1946 , it has 6.5:1 cr 125 psi cranking .
pull the spark plugs and put about 1 oz. of oil in each cylinder ,crank it over to dispel the excess install the plugs and pour an oz. or so of gas down the carburetor and start it up .
 

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My book only goes to 1946 , it has 6.5:1 cr 125 psi cranking .
pull the spark plugs and put about 1 oz. of oil in each cylinder ,crank it over to dispel the excess install the plugs and pour an oz. or so of gas down the carburetor and start it up .

I agree. Many years ago I was taught that a gas engine needs at least 80 psi cranking to start. I have since worked with many old tractors and worn out equipment. The quick and dirty way to start one is to ensure you have spark to the cylinder. You have fuel to the cylinder. Then to seal the rings. Oil s introduced to the cylinder to seal the rings.

Also helps to crank it with a 12 volt battery. Keeps the cranking speed high and won't hurt anything if done sensibly.

For many years my old forklift was started this way. Till it got so bad I couldn't use it for the blue acrid smoke all the time. Remove the plugs. Three shots of thirty weight from a pump oil can in each cylinder. Clean and replace the plugs in the cylinders. Pray it starts on the first few cranks or repeat the procedure. :thumbup:

That old engine was so worn out that a .060" bore job didn't clean the cylinders. The oil rings were worn to where they fell off the pistons in pieces and the compression rings were worn to less than half of their original thickness.
 

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Discussion Starter · #7 ·
I forgot to mention but yes I am getting plenty of fuel flow as well as I have tried to start it with oil in the cylinders as well as gas and ether through the carb itself.
 

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starting fluid.

Have you tries using a spray can of starting fluid. also come carb cleaner will help an engine start. My 2 cycle
weed whaker sometimes needs a shot of carb cleaner to start.
 

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Discussion Starter · #9 ·
Update

For those of whom might like to know a little of progress on the car. We set her up for a tow start and within 10 yards it was spitting smoke out so thick it looked like a cloud factory. We even drove it down the road for the first time in over 40 years!! I have done some fine tuning and and can now hop in turn the key and it starts right up. Thanks for all who contributed and offered advice.
 
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