1945 Farmall M Vapor Lock

How do you solve a vapor lock on a Farmall Model M?

with a good vented fuel cap.

M Farmalls have a gravity feed fuel system. Italso has staal fuel lines that are not close to hot engine components or exhaust. As Rustred points out, the only way to get vapor lock is to have a plugged up vent in the fuel cap. (this would cause the fuel to fail to be delivered to the carb.
Tell us more about your symptoms. (also if you have a fuel filter other than the sediment bowel and the screen at the carb, remove it, they are (usually) not designed to operate with only gravity power. Jim

The M just won't start. It's getting fuel to the carb and I've removed and checked the sediment bowl and fule line. All clear and flowing. An old timer told me that's it's a vapor lock at the engine. She'll turn over and want to start but won't.

Lots of reasons your tractor won't start even though there is gas to the carb. Some that come to mind include: weak electrical system, flooded engine, vacuum leak between carb and intake valves, plugged jets in carb, something wrong with the choke, valve problems. Does your carb leak gas if you crank the tractor alot and it doesn't start? I'd start by pulling the plugs, see if they are wet and see if you have good spark on them. While you have them out see if you have good compression. You have to start eliminating potential problems to find out where the real problem is at.

Here is a quick run down of what I've done.
1. Replaced plugs and doubled check gap. The old plugs were black and sooty. Good spark to plugs. .025.
2. Rebuilt and cleaned carb. Extra careful on the replacement of adjusting screws. Put in a new choke plate and choke seems to be working fine.
3. Removed fuel supply hose and cleaned with air hose.
4. Checked coil. Coil is fine.
5. Replaced points and condensor. Doubled checked point gap. .020
6. Checked plug wires. Seem to be in good shape - one boot was split.
7. Put propane bullet heater on carb side of engine with a tarp over the other side to warm things up.

All that and she'll try to start, but won't fire. It's almost like the on-off switch is off. Ran like a top until it got really cols about 3 weeks ago. Now won't fire. Any guidance would be welcome.

Can you get a steady stream of fuel out of the fuel bowl drain?

Yes - I do get a steady stream. An old timer stopped by to say the vapor lock was up in the intake manifold.

Vapor is all that is found in the intake manifold. Thus not really possible. Manifold issues can happen but they are rare. Common issues are cracks to the outside letting air in diluting the mixture so much that it doesn"t run. Loose manifold nuts allowing the same air leak into the head at the flange. These two can be pretty easy to find bu looking carefully at the casting for cracks, and if someone helps by cranking the engine while a (unlit) propane torch is directed to the head to manifold area to feed in fuel with the air leak.
The third manifold issue is internal between the exhaust heat to intake joint and can be a crack that is hidden letting exhaust enter the intake.
not common but possible.
I think that holding your hand over the intake at the carb while it is being cranked to start (be careful to be in neutral with the clutch blocked down to reduce drag on the engine)
If powerful suction is found, or it starts, the choke plate might not be centered in th intake bore. If poor suction, the manifold could be cracked as described, or the valve timing could be off.
If no joy, spark should be checked on each plug making sure the spark is crisp and blue, not yellow and thready.
If good, a compression check is next.
All these tests require a good charged battery and fair to strong cranking speed.
Pull starting it is another good option if you and another person are adept at the process and careful. Be safe. Jim

Did you clean the points after you put them in? Was that new condenser checked, as some are leaky when new. How far will the spark jump off the end of the plug wires?

Remember,

The term "vapor lock" is a two sided expression which really means:

"I'm trying to impress you with my knowledge, but in fact, I HAVE ABSOLUTELY NO IDEA WHAT IS WRONG." :>)

Allan

Here is a simple test to tell if your points are working. Attach a test light to the primary terminal of the distributor and the other end to ground on the tractor frame someplace. With the ignition switch on the light will glow if the points are open. If the points are closed you will not see any light. Now crank the engine the light should blink at you because the points are opening and closing.

Now, lets do a little troubleshooting.
1. If the points are open and no light, you are not getting power from the switch through the coil to the points.

2. If the light glows and does not blink/flash while cranking your points are not closing letting power go to ground charging the coil.

Post back with your findings and I'll help you.
Charlie U

(quoted from post at 08:56:47 02/16/14) Remember,

The term "vapor lock" is a two sided expression which really means:

"I'm trying to impress you with my knowledge, but in fact, I HAVE ABSOLUTELY NO IDEA WHAT IS WRONG." :&gt

Allan

Click to expand...

BINGO!!!

Allan is 100% correct. Vapor locking was a somewhat common problem on cars 30 or 40 years ago. Since then it has become a common excuse for an engine that won"t start used by those who have no clue what they are talking about. There are a lot of things that might be causing your old M not to run but vapor locking is not one of them. No offense to your old timer friend. If you have compression, fuel, and spark, it almost has to run. It sounds like you have plenty of fuel to the carb but is your carb functioning properly? Double check the status of your ignition system by following some of the procedures outlined by others. If carb and ignition check out you are left with compression. The fact that the tractor does not even try to fire leads me to believe you have an ignition problem.

I'm going to start using that!

take the plugs out of it and give all the cylinders a healthy shot of WD40. If it fires and runs for a few seconds you have a fuel problem. If it does not you are not getting any spark. Make sure the float in the carb is not sticking.

Charlie
So I did your test and all is working properly. I put in a new coil just to be sure and I'm getting nice blue spark at all the plugs. I did a compression test and all 4 cyl. Are at 90 psi. It tries to start but won't stay on. I emptied the fuel tank and added fresh gas as well. Good flow from the tank to carb and the carb bowl fills fully. I'm at a loss here. Never did this before.