Vapor lock 1 and 2

[1952henry]

George, your tests and analysis's are greatly appreciated. I'm sure you already know that or you wouldn't be doing them. What they do in fact is dispell or confirm long standing theories and/or myths, and provide food for thought about projects we can all do to stay on the road. I think this particular test is one of your better uses of mind power over mechanical impotence!

Now, food for thought regarding the 1 lb check valve you propose: I see no downside in its installation beyond just complicating a simple solution, but question the need for it in the first place. First, you reported that the sight glass showed no significant movement with the return line open or closed, so the reported engine spin of 4 or 5 revolutions shouldn't have been fuel related. Second, a negative pressure in the line theroetically could pull fuel into the pump as it is being sucked out, as both pump valves are forward directional. However, if the pump does in fact drain back, the fuel in the carb should be adequate to prime the pump again, wouldn't it? Perhaps these questions can be addressed at your next test run?

You are referring to the fuel in the carburetor being adequate to start the car in order to get the fuel pumping, correct?

 

[ford38v8]

You are referring to the fuel in the carburetor being adequate to start the car in order to get the fuel pumping, correct?

yes

 

[donald1950]

old henry's souloution would have resolved gary365's problem with a momentary ON switch when the fuel boils.
i ran a small inline fuel pump full time along with the mechanical for many years in 100 degree days here in south texas and never experianced any vapor lock after its installation.
a small in line pump wheather part time or full time seems to me to be a sensable, and easy, souloution to this whole return line, computer fan blowing on the fuel pump, insulating fuel lines, pouring water on teh fuel pump, ect experimentation.
sorry to say, but with all the complex effort on this vapor lock problem, although the insulated spacer is a great idea, with a small on line pump (part time or full time) like what old henry has been advocating is a simple and quite effective souloution and simple.. worked quite well for me.
we will be living with ethenol as an additive for the forseable future. the inline pump is a simple fix......
just my thought........ don

 

[Old Henry]

As I said before, as well as the return line may work for preventing vapor lock while running, even idling, I still don't think the return line will keep the mechanical pump from vapor locking after the car has sat in the sun on a hot day with the engine off. It will be interesting to see.

 

[G.M.]

George, your tests and analysis's are greatly appreciated. I'm sure you already know that or you wouldn't be doing them. What they do in fact is dispell or confirm long standing theories and/or myths, and provide food for thought about projects we can all do to stay on the road. I think this particular test is one of your better uses of mind power over mechanical impotence!

I didn't do the tests to be appreciated, or fame, I do them to solve my own personal problems with my old fords and I don't mind sharing the results which people can use if they want. This was the same purpose for the diode, coil, water pumps, 3 lb valve, center bearing, flex hose, modified 330-180 stats in the hoses and the vented carb spacer. These were all developed and tested for my own use and for a few friends. These products turned into business ventures for others. I have the experience from my manufacturing experience to step by step test for and isolate problems. This takes time and the right tools and equipment and you can't be in a rush or think with one ride around the block the problem is solved. To me this is fun. When I get into a project it's almost a 24 hour day, I even dream about them.

Now, food for thought regarding the 1 lb check valve you propose: I see no downside in its installation beyond just complicating a simple solution, but question the need for it in the first place. First, you reported that the sight glass showed no significant movement with the return line open or closed, so the reported engine spin of 4 or 5 revolutions shouldn't have been fuel related. Second, a negative pressure in the line theroetically could pull fuel into the pump as it is being sucked out, as both pump valves are forward directional. However, if the pump does in fact drain back, the fuel in the carb should be adequate to prime the pump again, wouldn't it? Perhaps these questions can be addressed at your next test run?

You have to read my post again, I already explained EXACTLY WHY the check valve is required. When you shut the engine down and the fuel draws a 1/2 to 1 lb vacumn on the carb line and pump draining back it needs to be corrected. Why do you think they put a check valve in the pump?? Without the valve in the pump the fuel in the carb line, pump and tank to pump line would all drain back. The pump valves have very light springs and I wouldn't be surprised if the vacumn created by the return line drain back wouldn't open the pump valve?? It takes quite a length of time to fill the line, filter bowl and pump when the fuel drains back. In doing some research all the cars I found with return lines all had check valves.
I already addressed all the questions I think are required. Maybe it's time for you do a little hands on testing or wait for the final results after which I will post my findings. G.M.

 

[G.M.]

Found an Airtex fuel check valve, all brass with 1/4" male pipe in and out. $10.00 at sears, $14.00 Auto Zone. Emailed Airtex to find the operating or spring pressure. Ordered 2 from AZ will be in tomorrow and will try one on Monday. Couldn't up load pictures, new camera has to much resolution so I have to reduce the size to upload to Fordbarn. Will fool with it tomorrow. G.M.

 

[joe 1950]

your on the rite trail, the fuel now days you have to look for anything without corn squeezins, back in the 1980s I worked for a Plymouth dealer, and on hot summer days custmers complained about stalling out , me and another old timer new it was vapor lock since these carburators sat over the exhaust manifolds, just like a coffee pot they would perk over, then Chrysler came out with a kit to install with a electric fuel pump and line kit to return hot fuel from the carb back to the tank keeping fresh cool tank fuel in the carb at all times , fixed the problem, I haven't had any stalling problems with my 50, but long crank time on hot soaked motor until I quite using gas with the corn in it, hope this helps

 

[G.M.]

What I have been wondering is if I return the maximum fuel to the tank and the fuel tank gets low on a 100 degree day with the high road heat under the tank how hot the fuel in the tank might get? By maximum fuel I mean having just enough fuel to maintain 75 MPH and returning the rest. This would give maximum cooling of the pump but also heat the fuel in the tank more. I may have mentioned this but for a trip on real hot days fill the tank in the morning before leaving with cool gas out of the under ground tank and it should stay cool until the next fuel stop. This would be rare but a lot of us have made long trips on hot days and had problems. G.M.

 

[Old Henry]

What I have been wondering is if I return the maximum fuel to the tank and the fuel tank gets low on a 100 degree day with the high road heat under the tank how hot the fuel in the tank might get? By maximum fuel I mean having just enough fuel to maintain 75 MPH and returning the rest. G.M.

At 75 mph getting 15 mpg that's only 5 gallons per hour or 1¼ cups per minute! The stock mechanical pump at idle pumps one pint per minute or 7½ gal per hour. At highway speeds typical fuel delivery volume is .5 US gallons (two quarts or 8 cups) per minute or a pint in 15 seconds. That is 6.4 times the flow necessary at 75 mph. I don't think you need to worry about sufficient volume or flow at 75 mph.

(Pump output specs from here: http://www.fordbarn.com/forum/showthread.php?t=112181)

 

[G.M.]

At 75 mph getting 15 mpg that's only 5 gallons per hour or 1¼ cups per minute! The stock mechanical pump at idle pumps one pint per minute or 7½ gal per hour. At highway speeds typical fuel delivery volume is .5 US gallons (two quarts or 8 cups) per minute or a pint in 15 seconds. That is 6.4 times the flow necessary at 75 mph. I don't think you need to worry about sufficient volume or flow at 75 mph.

(Pump output specs from here: http://www.fordbarn.com/forum/showthread.php?t=112181)

Read my post again. I am taking fuel from what is being supplied to the carb by letting some portion return to the tank. What portion I don't really know I can only look in the filler neck and see more or less fuel being returned. I put the return fitting about 5"s down in the filler neck so I could see the fuel being returned. I can also watch the carb line pressure gauge and see the pressure drop as I open the return needle valve returning more fuel. With the return needle valve wide open I can only get the pressure gauge down to about 1 1/2 lbs. This indicates the .130 ID of the return line is now the restrictor. There will be some point at which there won't be enough fuel to go 75 MPH. At this point of diminished fuel supply to the carb it may only go 60 MPH or even less depending on how much fuel is supplied to the carb fuel bowl. At this point the needle or in my case the ball valve in the carb will remain wide open with the fuel level in the bowl being controlled by the metered amount of fuel coming into the bowl. I think the engine would not run at a steady speed as the supply would vary some. The metering device is the amount of fuel being returned through the fuel return line back to the tank. From what I have seen on the carb fuel line pressure gauge I will never be able to return enough fuel through the return line to get to the fuel starvation point at 75 MPH. Why, because the approximately .130 ID of the 3/16" return tube. The .130 ID is a restriction metering the amount of fuel returned. If I installed a 1/4" return line then I could return enough fuel to starve the engine at 75 MPH. G.M.

 

[Old Henry]

Since the mechanical pump produces over 6 times the volume necessary to sustain 75 mph you can return 5/6 of the fuel by the return line and still have enough flow into the carb. As you said, your return line that's smaller than your supply line will create sufficient pressure and flow without any further restrictions. I figured that all out when I was about to install a return line but then figured out that it won't help with my most common vapor lock problem - starting the engine after sitting hot out in the sun shut off for 10-20 minutes. Oh, it starts OK because all of the fuel hasn't boiled out of the carburetor but since the gas has all boiled out of the pump after going a few feet the engine uses up the gas in the carb, hasn't got any more from the pump, and dies and won't start again. I don't see a return line helping with that problem. It will be interesting to see if it does on yours.

 

[G.M.]

It will work, NO doubt about it. And with Bob Shewmans 1/2" vented spacer under the carb there will be little and I suspect NO lose of gas after shut down in the carb. But I don't have to guess about this. I have a fuel sight glass on the carb and will leave it on for a month which shows the fuel level in the carb bowl at all times. So next week I will drive the 39 and do a few other checks on the return line and when I get back cover the radiator and get the temperature up to 200, shut the engine down and won't open the hood until the next day and will see how much fuel is in the carb. Pretty simple and then I know what's going and not be misled by guess's. G.M.
G.M.

 

[Old Henry]

What you really need is a "sight glass" for the fuel pump. That's where the vapor lock hits mine. Carb has plenty of gas to start but then dies 'cause the pump only has vapor in it. Maybe it's an altitude thing. Guess I won't know unless you can test yours at 5-10,000 feet where I live and drive. Shucky darn. Guess I'll just have to keep relying on my handy dandy electric fuel pump.

 

[G.M.]

You don't need a sight glass on the fuel pump. All you need is a laser pointed thermometer. When the top of the fuel pump gets to 135 degrees your in trouble. My pump will no longer get near 135 with the fuel return line will post the results later this week I expect the pump to remain below 125 degrees with the return line. A pressure gauge in the carb line will also show you when a vapor lock is coming. Fuel pressure drops as the pump gets hotter and when a full vapor lock is starting the gauge drops to a little less than 1 lb and starts jumping from less than lb to about a 1 lb and a half. G.M.

 

[G.M.]

At 75 mph getting 15 mpg that's only 5 gallons per hour or 1¼ cups per minute! The stock mechanical pump at idle pumps one pint per minute or 7½ gal per hour. At highway speeds typical fuel delivery volume is .5 US gallons (two quarts or 8 cups) per minute or a pint in 15 seconds. That is 6.4 times the flow necessary at 75 mph. I don't think you need to worry about sufficient volume or flow at 75 mph.

(Pump output specs from here: http://www.fordbarn.com/forum/showthread.php?t=112181)

The gas available IN the carb is reduced by the .098 hole in the carb needle valve input. You need to calculate how much fuel will flow through a .098 hole. Also this amount varies with pressure. What is it at 2 lbs, 2.5 lbs and 3 lbs. The pressure of the fuel pump remains the same from idle to higher RPMs. Once the pressure is adjusted by pump spring, stroke and push rod length it stays pretty stable. With a pressure gauge in the carb line there is no change in fuel pressure at various RPM's.

 

[Old Henry]

The gas available IN the carb is reduced by the .098 hole in the carb needle valve input. You need to calculate how much fuel will flow through a .098 hole. Also this amount varies with pressure. What is it at 2 lbs, 2.5 lbs and 3 lbs. The pressure of the fuel pump remains the same from idle to higher RPMs. Once the pressure is adjusted by pump spring, stroke and push rod length it stays pretty stable. With a pressure gauge in the carb line there is no change in fuel pressure at various RPM's.

At 1 lb. of pressure 12 gallons per hour will pass through your .098" hole. That's still over twice the volume you need to sustain 75 mph (5 gph). At 2 lbs. it's 17 gallons per hour (3 times the amount needed) and at 3 lbs. 20.8 gallons per hour (4 times the amount required). So, no worries about volume.

 

[G.M.]

At 1 lb. of pressure 12 gallons per hour will pass through your .098" hole. That's still over twice the volume you need to sustain 75 mph (5 gph). At 2 lbs. it's 17 gallons per hour (3 times the amount needed) and at 3 lbs. 20.8 gallons per hour (4 times the amount required). So, no worries about volume.

I wasn't worrying about my car I knew I would have plenty of gas. I just thought you needed something to do. Thanks for figuring it out. What has always made laugh is these guys with dual carbs putting on 3/8" fuel lines when the gas is going through a .098 hole. There is more than enough gas coming from a stock pump and the 1/4" line to feed 3 carbs. G.M.

 

[Old Henry]

What has always made laugh is these guys with dual carbs putting on 3/8" fuel lines when the gas is going through a .098 hole. There is more than enough gas coming from a stock pump and the 1/4" line to feed 3 carbs. G.M.

Yeah, that's like the guys who use 8-10 ga. wire for the speakers in their cars. Talk about overkill!

 

[G.M.]

Had some time this morning and put the Airtex fuel valve on the 39. I took off the return line needle valve so the only restriction in the return line is the little over 1 lb fuel check valve and the .130 ID of the line. If larger return tube is used one of the fittings will to have about a .125 orfice.to restrict the amount of fuel returned. So now all I have is a "T" in the carb line, the fuel check valve and the 3/16" OD return line which is steel brake line. I started it up and the fuel pressure at about 350 to 375 RPMs idle is 1.5 lbs.
Speed the engine up to 450 to 475 and fuel pressure go's to 2.5 lbs. This is lower fuel pressure because a good potion of the fuel is being returned to the tank. Without the return the pressure was 3.5. Let the engine warm up to about 160 and checked the temperature of the gas tank which was 77 degrees so we will assume the fuel was 77 degrees. At 160 engine temp I checked the top of the fuel pump, 95 at the top and 126 at the bottom. Checked the fuel bowl on the carb, 85 and the intake manifold below the carb, 158. This is something I forgot about, the cool fuel cooling the carb.
Wouldn't get over 175 degrees as it was only 75 outside. I put the fender cover over the radiator and left it run about 20 minutes and got it up to 210 degrees at the bottom of the top radiator tank. Top of fuel pump now read 93 and bottom of pump was 126. carb was 84 at the fuel bowl and 172 on the intake flange. I still have the fuel sight glass on the carb so I can watch the fuel level in the carb. I shut the engine down, closed the hood and tomorrow I will see where the fuel level is in the carb.
This looks better than I thought it would. NO MORE VAPOR LOCK. G.M.

 

[G.M.]

Went by the shop this morning and after hot shut down with the hood closed all night the fuel in sight glass of the carb fuel bowl showed right on the full line.
No lose of fuel in the carb. Even with a low battery I hit the starter and it fired right up on the first turn. This was a result of cool gas and Shewman's ventilated 1/2" carb spacer. G.M.