Update on Vapor Lock and Changes made with Gas Cap/Sig difference in the 2 caps

[msmaron]

Made some small changes today, The first was i noticed a leak in the side bowl of the carb, not that has anything to do with Vapor lock but it needed to be replaced, also took off my gas cap and WOW...NO VENT at all, That was a problem and i dont know why i did not look more closely yesterday. Filled up with better gas and drove. A difference already, Tomorrow back to driving to work for another test and i am going to insulate the gas line with what Tom is sending me. But look at the difference in the gas caps. The REPO which has the vent is larger and more sturdy. Wondering how exactly the VENT helps the vapor lock to prevent it??

[ford1]

a vented cap doesnt prevent vapor lock, what it does is allow air into the tank replace the fuel that is used, that way a it prevents a vacuum lock which wont let any fuel run out of the tank

[msmaron]

ok that makes sense and important..thanks for that lesson..always helps

HOWEVER,, by not allowing fuel to run out of the tank, it can cause a ?Stall?..maybe not the vapor lock but problems?

[John LaVoy]

Mark,
We had a problem with vapor lock coming back from Texas. You didn't say where you were having the problem, but in some states, CO being where we had the problem. The fuel mix included quite a bit of ethonal and lower octaing rating. That along with higher temperatures it was around 90 degrees I think, it causes the fuel to boil and creates the vapor lock. The solution we found was to switch to premium grade fuel. Ended the problem for us. We wrote this up in the Model A Times when it happened.

[msmaron]

Originally Posted by John LaVoy

Mark,
We had a problem with vapor lock coming back from Texas. You didn't say where you were having the problem, but in some states, CO being where we had the problem. The fuel mix included quite a bit of ethonal and lower octaing rating. That along with higher temperatures it was around 90 degrees I think, it causes the fuel to boil and creates the vapor lock. The solution we found was to switch to premium grade fuel. Ended the problem for us. We wrote this up in the Model A Times when it happened.

I am in chicago and it was about 92 that day, i have been told by many to switch the gas in the summer to a higher octane for that reason also. Thanks

[ford1]

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yes it will cause the engine to stall, basically its like running out of gas

[James Rogers]

Originally Posted by msmaron

Made some small changes today, The first was i noticed a leak in the side bowl of the carb, not that has anything to do with Vapor lock but it needed to be replaced, also took off my gas cap and WOW...NO VENT at all, That was a problem and i dont know why i did not look more closely yesterday. Filled up with better gas and drove. A difference already, Tomorrow back to driving to work for another test and i am going to insulate the gas line with what Tom is sending me. But look at the difference in the gas caps. The REPO which has the vent is larger and more sturdy. Wondering how exactly the VENT helps the vapor lock to prevent it??

What you have is a radiator cap being used as a gas cap. They are both the same in looks but work exactly opposite. I didn't think you had a vapor lock when you first posted before but, I am a naysayer. To see what will happen with your scenerio, use a half tank of gas and put a layer or two of saran wrap on the filler and hold it in place with a rubber band. If you get more than 2 miles before the car quits you will be lucky. 3 miles would be almost impossible. Try this after you insulate the fuel line and you will see.

[Ed Saniewski]

If I may suggest an experiment, after all the vapor lock changes are made. Wait a week then go back to the old gas cap and see if the problem comes back. This will prove a vapor lock or a lack of gas tank vent. Let us know.

[Dennis L Oberer]

In my recent article for the Restorer I mentioned that cap problem as one of the first reasons to check why the engine wont start or wont stay running. Lots of radiator caps end up on the gas tank and the quick way to tell is how I mention it in the article.

I know from personal experience as I had this happen to me once upon a time.


Dennis L Oberer
Green Bay WI

[msmaron]

Originally Posted by Dennis L Oberer

In my recent article for the Restorer I mentioned that cap problem as one of the first reasons to check why the engine wont start or wont stay running. Lots of radiator caps end up on the gas tank and the quick way to tell is how I mention it in the article.

I know from personal experience as I had this happen to me once upon a time.


Dennis L Oberer
Green Bay WI

Dennis let me go get the article and take a look, is it the issue with Reds car in the cover?
Mark

[msmaron]

Originally Posted by James Rogers

What you have is a radiator cap being used as a gas cap. They are both the same in looks but work exactly opposite. I didn't think you had a vapor lock when you first posted before but, I am a naysayer. To see what will happen with your scenerio, use a half tank of gas and put a layer or two of saran wrap on the filler and hold it in place with a rubber band. If you get more than 2 miles before the car quits you will be lucky. 3 miles would be almost impossible. Try this after you insulate the fuel line and you will see.

AND what does this result of the not being able to drive tell me..."No VENTING" via the gas cap was the culprit??

[Marco Tahtaras]

A gas cap with a plugged (or missing) vent will cause a problem for sure. However the gas and radiator caps on '30-31 models are not interchangeable! That only applies to the '28-29 type caps.

[Jason in TX]

Yeah. Your carb is sucking gas out of the tank. If there is no vent, eventually it would in theory create such a vacuum as to start imploding the tank.

The same theory as if you had an air tight bottle full of water and a straw. Start sucking the water out of the bottle using the straw. if you kept drinking without letting air it, it would start caving in the bottle, and would be really hard to suck the water out.

Your carb is having a hard time sucking the gas out of an air tight tank. When you sit, air gets back into the tank and it works again.

You don't want a vented cap on a radiator because the water would bubble out the cap.

[msmaron]

Originally Posted by Marco Tahtaras

A gas cap with a plugged (or missing) vent will cause a problem for sure. However the gas and radiator caps on '30-31 models are not interchangeable! That only applies to the '28-29 type caps.

Well all signs seem to point to that this was or part of the problem, Thanks for the insight and hope all is well Marco!

[Bob A.]

Forget about dressing up your fuel line. You found the problem. IMO "Vapor lock" is caused by three things in a Model A ford with gravity feed fuel system: No vent in fuel tank-Bad coil windings-Bad condenser. This is my opinion and I'm sticking to it.

[Bob A.]

Originally Posted by James Rogers

What you have is a radiator cap being used as a gas cap. They are both the same in looks but work exactly opposite. I didn't think you had a vapor lock when you first posted before but, I am a naysayer. To see what will happen with your scenerio, use a half tank of gas and put a layer or two of saran wrap on the filler and hold it in place with a rubber band. If you get more than 2 miles before the car quits you will be lucky. 3 miles would be almost impossible. Try this after you insulate the fuel line and you will see.

Way to go James!

[Mike V. Florida]

Originally Posted by Bob A.

Forget about dressing up your fuel line. You found the problem. IMO "Vapor lock" is caused by three things in a Model A ford with gravity feed fuel system: No vent in fuel tank-Bad coil windings-Bad condenser. This is my opinion and I'm sticking to it.

I want to take a little closer look at why a bad vent could cause vaporlock.

Am I right that;

We all know that vapor lock is when air gets caught in the line or bowl due to "boiling" of the fuel in a hot engine compartment.

If you have a bad vent in the cap (missing or clogged) and if the gasket is old and not sealing properly you will get enough flow to keep the car running but not necessarly enough to keep the fuel line full. The engine runs, the carb sucks fuel out of the bowl and during times that the draw in minimal the fuel flows to refill the bowl.

Now if we add the heat from the engine compartment and the poor fuel amount in the line ,what is in the line is easier to be affected by the heat and cause vapor lock. Yes, no?

[David Cockey]

Originally Posted by Elrod

Yeah. Your carb is sucking gas out of the tank. If there is no vent, eventually it would in theory create such a vacuum as to start imploding the tank.

The same theory as if you had an air tight bottle full of water and a straw. Start sucking the water out of the bottle using the straw. if you kept drinking without letting air it, it would start caving in the bottle, and would be really hard to suck the water out.

Your carb is having a hard time sucking the gas out of an air tight tank. When you sit, air gets back into the tank and it works again.

You don't want a vented cap on a radiator because the water would bubble out the cap.

The carburetor does not suck gasoline from the tank. The gasoline which is sucked into the manifold is from the bowl. The bowl is vented to the atmosphere and always at atmospheric pressure. The gasoline level in the bowl is controlled by the float and float ("needle") valve. When the fuel level drops in the bowl the float valve opens and more gasoline flows into the bowl. No vent in the gas cap keeps stops gasoline from flowing into the tank.

Cars with fuel pumps are a different story. If there isn't a vent into the fuel tank then the fuel pump may cause the tank to collapse as it pumps fuel out of the tank since there won't be air to replace the fuel.

[James Rogers]

[QUOTE=Mike V. Florida;19367]I want to take a little closer look at why a bad vent could cause vaporlock.

An unvented cap/tank won't cause "vaporlock" (wives tale). What happens with an unvented tank/cap is, when you remove fuel/liquid from a container it must be replaced by an equil amount of something else such as another liquid or solid or gas (air). In the Model A fuel system the fuel is replaced by air unless the tank/cap is unvented. In that case the fuel flowing to the carb is not replaced and causes the tank to create a vacuum which will eventually overcome the effect of gravity and starve the carb with stopping the fuel. The only way to overcome this is to add a vent to the cap/tank or open the cap. I have this problem on my cabbie and have to leave the cap loose to defeat the vent. I have tried several repo caps and all the gaskets seem to eventually rotate with removing and installing the cap at fuel time till the vent is covered. When this happens I only get a couple of miles and the car begins to starve for gas and eventually quits. If I let it sit for a while it will start and drive a couple more miles and quit again. This distance is dependent on the amount of gas in the tank, more gas less miles less gas more miles before it quits.

I still don't believe in vaporlock in a gravity fuel system.

[Bob A.]

"I still don't believe in vapor lock in a gravity fuel system".

James I agree 100% with you.
Vapor lock is caused in cars with an external fuel pump where as the suction side /line to the pump may be too close to an exhaust pipe or other heat source. This is one reason why modern cars that are capable of running at high temperatures have their pumps placed in the tank where there will be no external suction line and run nice and cool.