Vapor lock in sediment bowl revisited.

RayP(MI) · May 21, 2012

Posted yesterday of problems with fuel vaporizing in sediment bowl, causing vapor lock on '49 JD "B". We were using it in manute loader service, and not pushing it hard. You could look into the top of the bowl, (from below) and see the bubble of vapor. Last time this happened, back when we had the hot spell in March, son was plowinging with 2 16" plow. Could actually see a couple of streams of bubbles rising off the bottom/side of the glass bowl. So we're sure it's happening in the sediment bowl assembly. Today the temperatures are qbout 40 degrees lower than yesterday, tractor was running fine. Neither time was water temperature excessive according to the temperature guage. (180 degrees or so.)

John B. · May 21, 2012

Is your fuel tank cap venting properly?
When you see those bubbles in the bowl remove your fuel cap and see if the bubbles stop!

TomH in PA · May 21, 2012

Is there a heat shield missing somewhere?

old · May 21, 2012

I agree with John and sounds like the tank is building up pressure in side and if and when that happens yep you get the bubbles and problems with it running as it should

PopinJohn · May 21, 2012

I agree with the others, check the cap on the gas tank. I've seen the gasket cover up the vent hole on one before. Uncovered the vent in the cap and problem went away.
MikeShelby

Indiana Ken · May 21, 2012

Vapor lock occurs on the suction side of a fuel pump. When fuel pumps were mounted on the engine they picked up heat from the engine, in addition the long suction line running to the fuel tank could be heated from the hot road surface or ambient air. As the pump lowered the pressure in the suction line the fuel would flash to vapor (boiling) if the vapor pressure of the fuel exceeded the pressure in the suction line. As a result the pump would pump vapor and no liquid would reach the pump.

This condition can not occur in a gravity feed fuel system. In the event the fuel is heated to the point the vapor pressure exceeds ambient pressure (boiling) the vapor simply bubbles up through the fuel line and exits through the tank vent. Liquid fuel continues to flow to the carb. In my opinion the bubbles in the sediment bowl can considered normal on hot day.

Other than verifying the fuel tank is properly vented I would look else where for the problem. Perhaps a faultly coil or condenser...?

BushogPapa · May 21, 2012

I have heard of those JD "B" tractors that will pull 2-14 in 4th gear and if you can pull 2-16, you have some pretty special ground...!!
Mine is plenty Stout and will only pull 2-14 in 2nd and 3rd...
Does your have a water pump..?
Mine does and will never get to 160, if I don't close the shutters..even in the Summer..
If yours was an "All-Fuel" tractor, and has been converted to Higher Compression, for Gasoline..there may need to be a Heat Shield added to the bottom of the Fuel tank...but, I think, trying to loosen the fuel cap, to let it equalize with the outside air and see if it will settle down..
As I recall, gasoline will Boil at 76 Degrees if un-pressurized...
Maybe an improvised Heat Shield would help if it kept the sediment bowl a little cooler...
The Exhaust Manifold may heat it up..but I have never had any trouble with that..just Moisture in the Mags, if they set out over night..!!

Ron..

36 Coupe · May 23, 2012

Air pressure can stop the flow in gravity feed systems.My band saw mill has a gravity feed blade coolant system.The tank is 6 feet above the discharge point.I can see air bubbles moving up the clear tubing.The flow is shut off at the end of the cut.When a new cut is started the valve is opened.You have to wait for the flow to restart.Friends and I had a cutdown Model A Ford we drove around woods roads in the 50s.If it ran out of gas we had to loosen the fuel line to get gas to flow again.My tractor ran out of gas while I was picking up branches.My gas can had a quart of gas in it.Put it in the tank.No start,sediment bowl had an air space.Loosened the bowl no flow.Sprayed starting fluid in the air intake, engine started.Air space disappeared.Still dont know why air bubbles move upward in the sawmill tubing while water is dripping on the blade.We know that air can stop the movement of fluid in baseboard heating systems.The blade lube tank has a vent in it.Windshield washer fluid is used in cold weather.

Vapor lock in sediment bowl revisited.

RayP(MI)

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John B.

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TomH in PA

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old

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PopinJohn

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Indiana Ken

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BushogPapa

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36 Coupe

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