Vapor lock 1 and 2

[1932 V8]

Old Henry, the way I am reading post 12 is GM is using that statement as an example and further down he states these are "what ifs" . No where does he say removing the needle/seat is what he is trying to do.At least that is the way I am reading it
And this is what we call "the internet" folks
Things read can be interpreted many different ways . That is why these discussions are tough to have via the net. I do enjoy them though. It's fun bouncing ideas and thoughts back and forth.
In my opinion GM is giving us facts as per what he is doing on his car. I personally am intrigued by the idea. There are a lot of variables but I for one am interested in his findings.

[1932 V8]

V8Coopman, I totally agree. Very well said !

[ford38v8]

Originally Posted by V8COOPMAN

The NEEDLE VALVE is being used to trim the by-pass pressure, NOT to be confused with NEEDLE and SEAT...two, distinctly-different animals. DD

OK now! That concept is clear to me now. Why couldn't GM have explained himself better? His only reference was to eliminate the needle valve with the pressure valve. Now we're talking about eliminating a manually operated needle valve for the return, not the float operated needle valve for the bowl. Old Henry's Einstein post applies here!

[V8COOPMAN]

I just read what GM said...explained himself fairly well. Clear as mud to me. DD

[scooder]

A simple "I'm talking about the needle valve used to calibrate the returned amount of fuel, not the needle for the float" would have saved all this fun.
Now that ambiguity is cleared up, I understand the thinking.
Thank you.
Martin.

[G.M.]

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Originally Posted by V8COOPMAN

The NEEDLE VALVE is being used to trim the by-pass pressure, NOT to be confused with NEEDLE and SEAT...two, distinctly-different animals. DD

You got it DD Besides I don't use needle valves in my 97 carb. I use the double ball valve provided by Uncle Max. These give a smoother fuel delivery to the fuel bowl. You can run the 97 with the top off and watch the level of fuel in the bowl. The balls deliver minute amounts of fuel all the time when fuel is entering the bowl. The fuel level never varies much. Most needle valves stick before moving and the level varies a 1/2". I have used these for 30 years and never had a problem with them. Prior to that I had carb flooding or no fuel problems. G.M.




These are the "spurious parts" removed
that I used to isolate the VL problem.
SP was Henry's words.

[G.M.]

I bite the bullet and drained the nasty gas and replaced it with 10 gallons of 10% ethanol. Engine started this morning with 1 revolution with the starter. Pump was at 4 lbs and adjusted the pressure to the carb using the adjustable needle valve in the return line to 2 3/4 lbs. The more flow through the return line the less pressure in the carb line. Even with the valve all the way open there will still be enough restriction in the return to maintain some pressure to the carb. If I had say a 3/8" fuel line I think I could dump enough fuel that the engine would stall. This is provided the valve and all fittings had a 3/8" hole through them. The fuel will take the path of least resistance.
With the fuel set at 2 3/4 lbs we made the 30 mile run for lunch, engine ran perfect all the way. I dropped down to 12 MPH as I made a turn and it pulled out nice and steady only to think latter it was in Columbia. Stopped for lunch measured the top temp on the fuel pump which was 122, opened the valve a few turns and the temp dropped to 110. This proves again the return fuel cools the pump. Not really, the extra flow of fuel through the pump is what cools it. I haven't opened the needle valve all the way and drove the car yet. I want to do this and see how it runs at top speed and what the carb line pressure is. After lunch it took 5 or 6 turns of the engine to fire. This is unusual, it usually fires on the first turn. Stopped 2 more times for 10 minutes each time and had the same starting results. Next time I stop I will turn the needle valve off at the same time I shut the engine down and see how it starts after 10 minutes. This could be a drain back through the return line problem. If so a 1 lb check valve at the adjustable needle valve will solve this. It was only 85 degrees today and the engine ran at 180 all the time with Bob Shewmans 180 stats in the hoses. I need temperatures up near 100 now and get in city traffic for the real test. I'm satisfied from what I have seen there will be no VL problem. G.M.

[scooder]

I've looked into the use of a return line for the fuel line. My thinking wasn't born from pump temp or vapour lock. Only because I've been lucky enough to have never had it. My thinking was born off multi carb setups. I feel that when using a electric pump with enough flow for high performance use, the regulator is wound down (pressure wise) so much that I'm sure it hinders flow at high demand. Really don't want a lean out situation with my foot to the floor.
I feel I could have my cake and eat it with a return line setup,
Thoughts on this?
many thanks
Martin.

[flatmotor40]

That is the way mine just started doing after cranking first with almost 1 spin of engine and then run it shut it down for 20 minutes or so crank for seems like 5-10 rounds before fires and seems to be on the flooded side but it is only with electric pump.Just started this this year.before 1 turn of motor and doing the fires up.I guess I will have to live with it.But my Farmall Cub started doing the same thing and just rebuilt carb so I see if it fixed it.I hate this crappy gas nowdays

[G.M.]

Originally Posted by flatmotor40

That is the way mine just started doing after cranking first with almost 1 spin of engine and then run it shut it down for 20 minutes or so crank for seems like 5-10 rounds before fires and seems to be on the flooded side but it is only with electric pump.Just started this this year.before 1 turn of motor and doing the fires up.I guess I will have to live with it.But my Farmall Cub started doing the same thing and just rebuilt carb so I see if it fixed it.I hate this crappy gas nowdays

It's hard tell if this condition is pumping fuel or lose of fuel in the carb after shut down. I hadn't noticed it before the return line but I have been busy with property projects and haven't driven the 39. I have a sight glass that mounts on the carb showing the fuel level in the bowl at all times. I think I will try and find it this morning and put it on then I can tell where the problem is. G.M.

[ford38v8]

George, a word of caution regarding the sight glass... Ford discovered that they were unreliable for indicating float level due to under hood air flow. If you can dampen the effect of the wind, it should work for you.

[G.M.]

Originally Posted by ford38v8

George, a word of caution regarding the sight glass... Ford discovered that they were unreliable for indicating float level due to under hood air flow. If you can dampen the effect of the wind, it should work for you.

Not much air flow over the top of a 39 deluxe engine that's one of the main problems as described before. G.M.

[Cartravel]

The use of a return line is an excellent idea.

I think there is some confusion in terminology in this discussion. A "check valve" is a valve that allows flow in only one direction. A "pressure relief valve" is a valve that maintains a specific pressure. You cannot set a check valve at a specific pressure, e.g. 2 1/2 psi. A pressure relief valve with a return line would work in place of the needle valve and would be an improvement IMO. expavr already mentioned that one is available.

[Steves46]

With all due respect, would blocking-off the stock fuel pump and running directly from an electric fuel pump with a pressure regulator eliminate the problem all together?

[Old Henry]

Originally Posted by Steves46

With all due respect, would blocking-off the stock fuel pump and running directly from an electric fuel pump with a pressure regulator eliminate the problem all together?

Yes. Or, run the stock mechanical pump and only turn on the electric when vapor locked like most people do.

[expavr]

Originally Posted by scooder

I've looked into the use of a return line for the fuel line. My thinking wasn't born from pump temp or vapour lock. Only because I've been lucky enough to have never had it. My thinking was born off multi carb setups. I feel that when using a electric pump with enough flow for high performance use, the regulator is wound down (pressure wise) so much that I'm sure it hinders flow at high demand. Really don't want a lean out situation with my foot to the floor.
I feel I could have my cake and eat it with a return line setup,
Thoughts on this?
many thanks
Martin.

When you set up a fuel delivery system for hi performance you should be building into that system fuel flow to keep the A/F ratio in the engine at or near optimum at WOT. This starts with the electric fuel pump which is continuously pumping the fuel at whatever maximum pressure is needed for WOT. When you're not at WOT the fuel pump which continues to pressurize the fuel line at the higher pressure is adding heat and possibly air thru cavitation to the fuel due to lack of demand in the carb. The fuel flow is "deadheaded" at the regulator it can go no where but to the carb where its not needed. A fuel return line sends the uneeded fuel supply from part throttle operation back to the tank where it blends with the cooler fuel in the tank. I came to this conclusion after several bouts of what I think was VL2 fuel starvation on a supercharged engine. Compare the fuel pressure your electric pump puts out versus the pressure on your fuel regulator. My guess is that you will find a big difference between the two and while some of that difference (2-3psi?) might be needed to compensate for line loss between the pump and regulator your electric fuel pump is operating well above the engine's fuel demand at part throttle.
I'm not familiar with how to setup a multiple carb system, but it would seem that if you set the fuel flow for engine demand at WOT based on whatever the carbs' design allowed the fuel delivery system should be able to maintain that fuel pressure to the carbs. Here I'm assuming that you're using a fuel log of some sort that feeds each carb. As far as leaning out at WOT this would be where the individual carb tuning would become important. I suggest raising that question on the HAMB web site.
Les

[gary635g]

Major vapor lock today temp near 90 here in Yuma hit the freeway and vapor locked very bad. I stoped and poured ~ 2 qts. of water over the pump restarted and drove 25 to 40 ~ 20 miles with the choke fully applied. I will do a pressure check tomorrow. After I got home I put a zip lock bag with ice and water in it over the pump and drove a bit it worked ok and beats peeing on the pump. Gary

[scooder]

Les, thank you for your reply, that makes sence.
Martin.

[G.M.]

I installed a sight glass tube on the 97 to watch the fuel level in the carb. Installed the carb this morning and put a pen line on the tube where I thought the carb fuel bowl level should be. Cranked the engine over to fill the carb and the fuel level came right to the bottom of the line. Started the engine, adjusted the fuel pressure with the return line needle valve to 2 3/4 lbs going to the carb. The fuel level in the sight glass stays at the line with 2 3/4 lbs adjusted pressure in the carb line, 3 1/2 lbs full flow to the carb and no return fuel with the needle valve closed or 2 lbs with the needle valve wide open. NO change in carb fuel level with the return closed or fully open with a 3/16 OD steel brake tube return line. If it runs at 70 MPH with the return line wide open there is no need for the return line needle valve.
NOW THE INTERESTING PART.
When I shut the engine down with the needle valve even PARTIALLY open the fuel gauge drops to BELOW zero showing about 1/2 lb of vacumn on the pressure gauge immediately at shut down and the fuel in the sight glass was slightly below the line.
At shut down with the gauge showing over 3 lbs and the return line needle valve CLOSED the sight glass was just over the top of the sight glass pen line. The differences of the fuel level in these two cases are so close it doesn't matter.
The thing that matters IS the pressure gauge showing a 1/2 lb of vacumn with the return line open at shut down, this indicates fuel is syphoning back the return line drawing fuel from the carb line and fuel pump. This will make restarting after sitting say 10 minutes a little harder as I experienced, it took 4 or 5 turns of the engine to start. With the return line CLOSED I had pressure that remained in the fuel pump and line for several minutes slowly bleeding down through the fuel pump check valve as described in the Ford service bulletins.
My conclusion is IF there is sufficient fuel to run the engine continually at 70 MPH with a 3/16" OD return line FULLY OPEN which I will have to measure the ID which is the important part then NO adjustable needle valve will be required. I believe the ID will be in the .120 to .130 range. I still have to road test at 70 MPH with the return WIDE OPEN.
We still have the fuel drain back through the return line pulling the fuel from the pump and carb line when the return line is even partially OPEN after shut down. A simple 1 lb check valve in the return line will solve that problem. It won't effect the fuel return because that pressure is above the 2 + lbs we get with the valve wide open and the check valve will shut off the return when the pump stops pumping when the pressure drops to 1 lb. There will be a little fuel returned as the shut down pressure drops from it's 2 1/2 to 2 3/4 lb to 1 lb.
Supposed to get around 90 next week so I can check fuel pump temperatures with the return working but I'm sure the VL problem in the pump is gone with the return.
While the carb fuel level sight glass is on I will check the effect of heat boiling the gas out of the carb after shut down. If fuel leaves the carb bowl I will see it on the sight glass. I don't think I will see much fuel lose with Bob Shewmans 1/2" vented carb spacer being in place. Pictures to follow. G.M.

[ford38v8]

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?