Copper fuel line for marvel

[tcslr]

I looked at photos and the fuel line from the fuel pump to carburetor has a loop. The loop aspect t is upward by that I mean loop us to valve cover. 
has anyone experienced vapor locking due to engine compartment getting hotter and the top loop (then fuel) eventually vaporizing…. I had a fuel starve issue and am wondering if that could be the problem?

am I over-thinking this? tilting at windmills?

Tom

 

[Morgan Wright]

37 minutes ago, tcslr said:

I looked at photos and the fuel line from the fuel pump to carburetor has a loop. The loop aspect t is upward by that I mean loop us to valve cover. 
has anyone experienced vapor locking due to engine compartment getting hotter and the top loop (then fuel) eventually vaporizing…. I had a fuel starve issue and am wondering if that could be the problem?

am I over-thinking this? tilting at windmills?

Tom

 

 

Fuel after the pump is pushed, fuel before the pump is pulled. Vapor lock happens when pulled, not pushed.

[smillard]

Vapor lock can and does happen after the fuel pump. It happens where the most heat is.  Todays gas evaporates much easier and quicker than gas from back in the day.    I had that problem and resolved it by adding a vapor filter after the pump and before the carb and return line from the vapor filter to the tank.  Keep the fuel moving and it wont have time to heat up and can't vaporize.

Edited June 7, 2022 by smillard (see edit history)

[Morgan Wright]

I don't think vapor lock is the correct term for vapor after the fuel pump. It happens, and it causes all kinds of problems, but it's not vapor lock, which is the term for vapor disabling fuel pumps and causing the car to stall. Vapor after the pump injects vapor into the carb causes rich mixture and other problems but it doesn't stop the flow of gas or "lock" it.

[32buick67]

Not sure how relevant this is, but last year I was using a copper fuel line in 90F ambient and I had no vapor lock issues while running and stopping/starting.

I recently changed to a 5/16 ID rubber fuel line this spring2022 for convenience because I was testing and tuning many Marvel carbs on my 32-60 engine, which included 90F days.

 

Small statistical data point - the copper or rubber lines between the fuel pump and Marvel carbs had no change in performance on multiple carb types over the last 7 months, which is a good thing.

Note, I rebuilt my fuel pump and ensure it was a healthy unit prior to these tests.

31-90 Pump:

 

Here are some specs on Buick fuel pumps, 31-90 included:

 

 

 

Hopefully this is helpful to folks.

 

 

[Bill - 29 Buick]

Tom:

 

I have experienced whatever it's called (I call it vapor lock) when the car ceases running as the gas presumably vaporizes in the pig-tail between the fuel pump and carb, in my 29 McL-Buick.

 

This happens when it's very hot (90+ or more) and I've been traveling at close to 60MPH for extended periods on black asphalt hwys. (long stretches of lighter coloured cement hwys. lower running temp. by about 5 degrees).  I can actually feel the car starting to seize-up - generally when climbing long hills.  To correct the problem, I flip on a low-pressure (2-4 lb) electric fuel pump which pushes gas into the carb.  

 

Like 32Buick67, I have also replaced the copper pig-tail line which screws into both fuel pump and carb with a rubber hose that slides on and off appropriate fittings on both.  Saves on damaging the screw fittings and is a whole lot quicker to get off and particularly back on.

 

Bill McLaughlin

1929 Silver Anniversary Buick Newsletter

1929 McLaughlin Buick Roadster

Edited June 10, 2022 by Bill - 29 Buick (see edit history)

[carbking]

Bill - the below is NOT an argument, rather an alternate possibility.

 

If there were vapor in the line, and the mechanical fuel pump functioning normally, then the pressure from the pump should push the vapor into the carburetor, and the carburetor bowl is vented, so excess vapor in the bowl would escape through the vent, and the carburetor would have the proper level of fuel in the bowl.

 

Another possibility is that you truly do have vapor lock, normally defined as vapor in the fuel pump itself. A diaphragm style fuel pump WILL actually pump vapor, just very inefficiently. So the bowl is being depleted as the pump is not pumping fuel. Now turning on the electric pump will push the vapor out of the mechanical pump through the fuel line, and it will vent through the carburetor bowl vent. Since the electric pump is not connected physically to that huge heat source (the engine), the electric pump works as it should.

 

Again, not arguing. You are there, and I am not.

 

Regardless of the location of the vapor, your electric pump is correcting the issue.

 

Jon

[Bill - 29 Buick]

Jon:

 

No argument from me. You are the carb expert.  I’m just a dedicated 29 McL-Buick driver.
 

Looking at your possibilities, I’d say that my occasional “vapor lock” is in my mechanical fuel pump, as you suggest. 

 

The nice thing is that the electric pump corrects it almost instantly. 
 

Thanks for your help. 
 

Bill McLaughlin

1929 Silver Anniversary Buick Newsletter

1929 McLaughlin Buick Roadster

 

[Mark Shaw]

 Most, if not all, mechanical fuel pumps are reciprocating diaphragm pumps that produce intermittent flow characteristics.  These pumps require more net positive suction head (NPSH) than rotary pumps because they start and stop the flow on each stroke cycle.  The weight of the liquid in the entire length of the suction line must be accelerated on each suction stroke of the pump.   The NPSH available (atmospheric air pressure) required for these fuel pumps is often exceeded when travelling at high altitude.  Higher temperatures exacerbate the problem by significantly lowering the vapor pressure of gasolines and alcohols.  So, when driving on a hot day and/or at higher altitude, these factors often result in vaporized fuel on the suction side of the original mechanical pump.  

     In my opinion, the simplest solution is to install an electric fuel pump close to the fuel tank to shorten the length of the suction line and pressurize most of the the fuel line ahead of the mechanical pump.  This secondary pump can also shorten initial start-ups for vehicles that tend to boil fuel out of the carburetor when shut down.  Just be sure to power electric fuel pump through the ignition so it cannot run with the ignition off.

     Another successful but more involved solution is to install a bypass fuel line from the carburetor inlet back to the fuel tank.  The bypass fuel line continuously replenishes the carburetor with cooler fuel from the tank to minimize heat exposure from the engine compartment while the fuel slowly refills the float bowl of the carburetor.   Heat shields and fuel line insulation can also work to minimize lower vapor pressure due to heat, but these solutions do not address the NPSH problem associated with reciprocating pumps.

Mark Shaw

My $0.02

 

 

 

     

Edited June 11, 2022 by Mark Shaw (see edit history)

[Morgan Wright]

This guy has a loop de loop on the suction side. But with the Stewart vacuum tanks it really doesn't matter, they can suck like a Hoover.

 

 

[tcslr]

Thanks, gents.

Mario - I replaced the rubber hose with period correct copper.

 

Bill, 

I have experienced mechanical pumps ‘locking up’. In cars, it is invariably been at high temps during extended operation. A solution is an intermittent electric pump - like you mentioned - that can be turned on ( instant switch)  and overcome ‘vapor’?

 

Another possible solution I’ve observed being used was adding 5-10% diesel or kerosene ( volume) to ‘reduce’ vaporization. 
 

Mark, 

that was a good basic summary of pumps and pressures. I’ve also heard about the recirc line.

 

What I’m - I guess asking - if one wants to keep a car dead original ( configuration) but constrained by modern fuels - let’s face it, modern fuel is light years better than what was available 90 years ago - even ethanol addition  - any tricks? To keep it going?

 

Tom

[Bloo]

1 hour ago, tcslr said:

What I’m - I guess asking - if one wants to keep a car dead original ( configuration) but constrained by modern fuels - let’s face it, modern fuel is light years better than what was available 90 years ago - even ethanol addition  - any tricks? To keep it going?

I remain unconvinced that modern fuel has to be a problem. The ethanol-laced stuff *IS* horrible, and can be damaging to old cars. I wish it would go away. I however do not believe that one cannot run it in an originally configured car in most cases. More often than not, it is an excuse to not fix a problem that might be rather hard to sort out. On the other hand some cars were always prone to vapor lock. Also some 1920s cars have really overdone the carburetor heat. You did not post make model and year. Beyond "Buick" and "Marvel" I have no idea. You might have an overactive heat riser.

 

But back to your question of what can you do. Run a fuel sock on your fuel pickup if at all possible. Check your fuel line from the tank to the engine with one end plugged and a mityvac at the other, and be sure it holds vacuum. This verifies that it has no pinholes. Don't assume you would see a wet spot from a leak, sometimes you do not see one. If any rubber hoses are used, make sure those do not have pinholes. Use 30R9 fuel injection hose. You don't need the pressure rating, but 30R9 is rated for Ethanol. It is also lined and will not develop tiny cracks which become leaks along the reinforcement strings as it ages. That was a common problem with the old hose used in carbureted cars originally. Make sure your mechanical fuel pump is getting enough movement at the diaphragm. On some cars the cam that drives the fuel pump can wear out and the diaphragm will not have enough movement. Sometimes this can be checked by bolting on a partially assembled fuel pump. Make sure the check valves in the fuel pump hold vacuum. Find some creative way to check them with the mityvac. Avoid at all costs having a fuel pump that has to be "wet" to prime itself. That is a recipe for disaster. On the other hand, a really good pump might re-prime before the carburetor runs dry. Replace any cork carburetor floats. Brass would be nice. If the float is to remain non-brass, use new natural cork (not rubber-and-cork-dust), or maybe balsa wood, or even <gasp!> nitrophyl. Seal the float with cyanoacrylate, or gas tank sealer, or something else that is impervious to fuel and also to ethanol. The original sealer was shellac, and ethanol dissolves shellac, so that won't do.

 

Edited June 12, 2022 by Bloo (see edit history)

[Mark Shaw]

On 6/11/2022 at 6:28 PM, tcslr said:

if one wants to keep a car dead original ( configuration) but constrained by modern fuels - any tricks? To keep it going?

By dead original; if you mean no electric pump or bypass, you will need to drive on cooler days and at lower altitudes. 

 

One more option is to install an accumulator on the suction side of a mechanical pump to keep the fuel flowing continuously.  I am not aware of any retrofit units available for gasoline applications, but some of the older mechanical fuel pumps have what appears to be an air filled dome that may work as an accumulator.