vapor lock additives or ideas

[tcslr]

Next week, we are taking the '32 Chevy on the Founders Tour.  The weather is to be hot and humid and I am wondering what problems we might have with vapor lock.  This periodically occurs when hot and longer days.  The engine is rebuilt and runs very well.  I did install an electric pump to help assist ( and I installed an isolation or kill switch normally leaving the electric pump un-energized).

 

Are there any additives that help reduce potential of vapor locking?  Someone mentioned Marvel Mystery oil - which I don't use.

 

The fuel line to the carburetor runs along the block and between the valve cover and gooseneck.  I suspect the vapor problems really occur in the mechanical pump as the engine eventually gets hot.

 

I'm just thinking are there any things that I can do to reduce the potential?  Certainly, opening the hood between stops helps.  Ultimately, it's part of the touring adventure but would be nice if it didn't happen - just trying to reduce the potential.

 

Thank you, Tom

[nickelroadster]

If you can find it, the best thing is to use non alcohol gas.  10% ethanol makes the gas boil at a lower temp so it vapor locks more readily.

[Spinneyhill]

What is vapour lock? The volatiles in the fuel boil off into a gas. In this country the octane rating is increased by adding aromatics, which have a low boiling point, hence they evaporate readily and are called aromatics. The lighter fractions start boiling off at about 90 to 100 F. As well, ethanol evaporates readily. Its boiling point is c. 173 deg. F.

 

So, use the lowest octane fuel you can get (fewer highly volatile aromatics in it). Then arrange some cooling or shielding of the fuel line and fuel pump. Move the fuel line away from the engine. If you add MMO, you are diluting the fuel but you still have the low boiling point aromatics in the fuel. I doubt it would be very effective.

 

Should the car have "dust pans" around the bottom of the engine? If so, does it have them? If not, try fitting some. It is my understanding they improve the cooling effect of the air flowing through.

[Sweet64rivi]

Here's a link to gas stations in PA that sell non-ethanol.  Not sure if any are near Huntingdon.  Maybe seek out a local  http://pure-gas.org/index.jsp?stateprov=PA

[Spinneyhill]

Some proper facts. Ethanol is not the problem. I found this quote in a document entitled "Ethanol Fuel Properties and Data Page" from

txideafarm.com
 

"Older automotive systems are much like conventional aircraft systems, in that fuel from the pump “dead-heads” against the metering device on the engine, waiting to be used. This is a hot environment, and the fuel gets hot while it waits to be used. The critical area is usually the low pressure inlet to the fuel pump. If the fuel begins to boil, the vapor bubbles cause the pump to lose its suction ability, and it ceases to pump fuel. This is vapor lock. Low boiling points, high RVP, and low latent heats of evaporation act to make this problem more severe. All gasolines have severe disadvantages relative to ethanol by any of these measures. In tests, neat ethanol has proven virtually impossible to vapor-lock."
 

Edited July 16, 2016 by Spinneyhill (see edit history)

[DavidMc]

Tom ,

In answer to your question about additives I have found adding kerosene reduces vapor lock, I haven’t tried Marvel Mystery oil as it is not available here in Australia.  Others have reported improvements with Diesel fuel but when I tried Diesel, it made no difference.  The problem with Kerosene is you need to dilute the fuel with at least 10 -15% for it to be effective and if all of the conditions are against you nothing works and I have tried everything. I have relocated the fuel line away from the exhaust system, fitted heat shielding, fitted a bypass electric pump removed the engine trays to allow more cool air around the engine, raised the leading edge of the hood to allow more air flow into the engine bay. But on a hot day when in stop start traffic or on a long climb none of the above are sufficient and a wet rag around the carburettor is needed but that is very temporary .  I have been on tour climbing and had to keep wetting the carburettor every 100 feet or so- not fun when there is no overtaking lane and traffic following.

Fuel is made up of many fractions with varying boiling points and the lowest boiling point fractions boil at very low temperature.  Adding kerosene does not change that but even though the theory may be unclear it has on many occasions been the only way I could keep running. 

Again I do not dispute the theory but I have found that octane rating makes no difference but 10% ethanol certainly does and must be avoided in hot weather.  In winter my cars will run perfectly on any fuel including 10% ethanol and, incidentally they run fine on 10-15% kerosene and I suspect would run fine on 100% kerosene once hot.

My cars are Packards of the 1920’s.  I have restored three and driven them all extensively over the last 30+ years and they have all vapor locked under the same conditions. Stop start traffic &  long climbs.

This is not a new problem.  I have copies of letters written by the Packard Motor Car Company to its dealers regarding the problem.  The first was written March 17 1930 headed “ Boiling Gasoline”.  Some quotations from that letter are interesting: “The combination of high operating temperature together with blended fuel including very volatile fractions has in some cases caused trouble through the boiling of fuel in the vacuum tank, the carburettor and the line connecting these two units ……”           A minor modification was suggested in the letter.  However, a further letter was sent to the dealers  some 16 months later dated July 31 1931 advising that the previous modification needed to be replaced with a  more drastic change where the carburettor float bowl  needed to be fitted with a vent connected to the intake manifold.  In that letter Packard referred to the above letter and stated in part:  “It will be well for you to read this letter again because the situation has become even more serious. The gasoline on the market today is more susceptible to vapor lock than the fuel of a year ago and the corrective measures at that time are not adequate today.

The problem of high volatility fuel is far worse today that it was in 1931 as modern fuels have become increasingly volatile which is not a problem for the cars of today as they operate with fuel under high pressure where the boiling point is far higher.

The problem seems to worse on some cars no doubt due to the proximity of the fuel system to heat.  The Packards have the vacuum tank over the exhaust manifold which combined with high under hood temperatures makes the problem worse than on cars where these conditions do no exist.

It is quite possible you will not have a problem particularly if you can keep away from hills and keep the car moving to keep the air flowing through the engine bay.

Good luck with your tour, let us know how it went.

[MCHinson]

I can only relate my personal experience with my 1937 Buick on the Sentimental Tour. As long as the temperature was under 95 degrees and I used non-ethanol fuel, I had no problem. With a temperature of 95 degrees and ethanol containing fuel, I had to use the electric fuel pump. If you can find non-ethanol fuel, I suggest you use it. If you have a problem be ready to flip the switch to activate the electric fuel pump. That is what works for me. Enjoy the tour.

[joe_padavano]

11 hours ago, Spinneyhill said:

Some proper facts. Ethanol is not the problem. I found this quote in a document entitled "Ethanol Fuel Properties and Data Page" from

txideafarm.com

 

Just out of curiosity, what exactly qualifies "the Johnson Family Homestead" as experts in the chemistry and physical properties of gasoline and ethanol?

[Spinneyhill]

Have a look at the Family and Friends link and then GW's page. GW is well qualified to write this.

Edited July 16, 2016 by Spinneyhill (see edit history)

[MCHinson]

Some more research is needed before I am going to assume that "GW" knows what he is talking about.  

 

Google tells me that the boiling point of ethanol is 173.1 degree F.

 

The boiling point of gasoline ranges between 104 and 392 degrees Fahrenheit.The wide range of boiling points is due to the many different blends of components available to provide different characteristics such as higher octane, lower fuel deposits and overall volatility.

 

https://www.reference.com/science/boiling-point-gasoline-4ee47a3b379ed4c2

[Mark Shaw]

Spineyhill is correct that fuel from the pump “dead-heads” against the float valve on the engine, waiting to be used & therfore has time to get hot in the engine compartment.  I learned from someone with a Packard Twin Six car (these cars had the fuel line running between the manifolds) to install a bypass back to the fuel tank.  The bypass allows the fuel to continuously return to the tank minimizing residence time in the engine compartment while continuously providing cool fuel from the tank.

[tcslr]

I'll try to find 100% gasoline.  Some folks mentioned adding 10-15% diesel ( or kerosene) - the rationale being that it will lower the vapor pressure OR 100% gasoline OR aviation gasoline ( 100 octane).  It sort of makes sense as the compression is low (5-1). 

I had a bad vapor lock event last year on Wednesday during the Founders Tour.  It was very hot ( mid 90s) and we had just made a longer run ( 35 miles?)  Typically I don't use the electric fuel pump but maybe need to be quick with the toggle ( cut-off) switch.

 

It is to be a hot week and I am a little nervous.  I hope for a problem-free tour - but seems every tour has something - especially since I like the older vehicles ( mid 30s and older).  electrical and generator one year ( ran off the battery but charged every night), water pump packing leak - and I hadn't brought additional -packing, vapor lock and generator/battery issue.

Tom

[DavidMc]

Some interesting information here but keep in mind that Tom’s original question was for ideas that work particularly the use of additives.   More comment on this would be of interest.

However picking up on some of the information, one of the main ideas that comes up every time vapor lock is discussed is avoidance of ethanol containing fuels and yet we learn that ethanol has a higher boiling point than the lowest boiling point fractions of gasoline which would lead you to conclude that ethanol fuels would be less likely to cause vapor lock. Are we just biased about ethanol because of its other negative effects?   My experience has been that it makes the problem worse but there is no doubt it is not the sole cause, any fuel will vapor lock in my cars under the “right” conditions.  There is no practical way, when you are experiencing the problem, to experiment with different fuels, you go for what you hope is the best available. 

Another comment that resonates with my experience is  “……..fuel from the pump “dead-heads” against the metering device on the engine, waiting to be used. This is a hot environment, and the fuel gets hot while it waits to be used”  

There is fuel in the engine bay moving very slowly through to the engine.  It is subject to high under hood temperature and radiant heat from the exhaust manifold.  The low flow rate allows plenty of time for the fuel to get hot.  The stored volume in the engine bay is large especially on car with vacuum tanks.  A solution is to fit a pump that keeps the fuel in circulation back to the fuel tank.  Ideally we want all of the fuel not flowing to the engine to be flowing back to the tank but there- in lies the difficulty.  The fuel flow rate to the engine is very variable over the range from idle to full power at high revs, but the return flow to the tank will be at a fixed rate.  That fixed rate needs to be restricted so that it does not starve the engine under any condition - with some margin for error.  This idea is discussed in great detail in a much earlier thread: 

http://forums.aaca.org/topic/213513-modern-fuel-vapors-and-a-54-bentley/?page=2

A problem with assessing  vapor lock cures is you cannot try something then drive the car down the road to see if it works.  The car may drive well for a long time until the conditions tip it over the edge.  I have friends who have made some change that they are convinced has cured their vapor lock but they rarely drive the car. Some long time later it is typical to find that what they thought was a fix did not work.

It’s a difficult issue and one that generates differing opinions a bit like the “what is the best oil to use” subject. 

When the weather is very hot and I am on tour my best fix has always been to add as much kerosene as possible, I don’t know why it works but does. 

[F&J]

2 hours ago, DavidMc said:

A solution is to fit a pump that keeps the fuel in circulation back to the fuel tank.

 

2 hours ago, DavidMc said:

Ideally we want all of the fuel not flowing to the engine to be flowing back to the tank but there- in lies the difficulty.  The fuel flow rate to the engine is very variable over the range from idle to full power at high revs, but the return flow to the tank will be at a fixed rate.  That fixed rate needs to be restricted so that it does not starve the engine under any condition - with some margin for error

Run this out there for some thought:

 

A early Bosch EFI I have, the pump is high pressure with reserve flow.  It runs at 28 psi to make the system calibrated from new.

 

There is a pressure regulator in the system, at the motor.  The pump runs the same speed at idle or wide open throttle.  The unused flow and excess pressure constantly gets pumped back to the tank. EFI does not need the return to prevent vapor lock, I know that.  But the byproduct of the system getting the pressure regulated,  is that gives a return system working full time. 

 

 

If someone could design a very basic return system for the old engine driven mechanical pumps we have, why would that not work?  Those pumps are capable of a lot more flow than the tiny bit needed for running.  You'd need something to regulate the pressure for the carb, but let the pump run at max flow to dump the rest to the tank.  ?

[Spinneyhill]

I think the next thing to find out, really, is whether the presence of ethanol causes any reduction in the boiling point of any fractions in the gasoline mixture. So far we know the lighter fractions boil at just about body heat. What about if we add ethanol?

 

[ply33]

First, my '33 can vapor lock: Typically after a long run (>30 minutes) at high speeds (60 MPH or so) in 95°F to 100°F temperatures. If after a run like that you stop the car and just idle, the engine can die. Or, alternatively, you park it for a few minutes (say to fill the tank), on a restart it will run fine for a short while until the carburetor bowl goes dry and then die. The quick fix for this is to cool the fuel pump down. Once back on the road with enough air flow through the engine compartment, the car will run fine again.

 

All of the above are observations from when driving in California.

 

We all like to complain about gasoline. Especially in California where our "special blend" is often blamed for much higher gas prices and a litany of various other problems.

 

A few years ago I drove the car to a meet in Arizona. It was April so the highest temperature was only in the 80s, far cooler than I'd experienced the above problems. But from the first tank of Arizona gas until I was able to fill the tank again in California I was continually battling vapor lock. I'd always figured California gas was "bad gas" and that the car would be happier with gas purchased in another state so this surprised me.

 

I then did a quick check and it turns out that part of the "special blend" is a requirement for a lower Reid Vapor Pressure in California (6.9 or 7.0 psi) than required nationwide (7.9 to 9.0 psi depending on state and season). So it seems, at least for my car, that California gas is better than elsewhere in the nation with respect to vaporizing in parts of the fuel delivery system where it shouldn't.

 

I guess I ought to mount an electric pump near the tank and rig it to a momentary switch to assist in starting after long storage and to compensate for the above vapor lock issue, but I really like keeping the car stock.

[Spinneyhill]

Back to my reference, George George (see above for full ref.). On p. 78 he discusses alcohol blended petrol.

 

"A Cooler Engine with Alcohol Fuel: due to the high latent heat of the alcohol, engine temperatures are generally lower when running on alcohol-blended fuels than when running on petrol and the greater the percentage of alcohol in the blend, the lower will be the temperature."

 

Hmmm. So that might mean you should get less vapour lock on E15 fuel.

[C Carl]

I am pretty sure I have posted this elsewhere. From "Marks' Mechanical Engineers Handbook" , 3rd Edition , June 1930. It explains the degradation , and resurrection of gasoline quality 1915 - 1930 or so. This corresponds perfectly with David's Packard info. I don't know about Packards or Chevvys or Plymoths , etc. and the extent to which they pre-heated the intake to deal with the low volatility components of this sad chapter of gasoline history. But I am very familiar with Cadillac , and have been told that Lincoln had similar exhaust heated intake. YOU MUST DROP THE INTAKE TEMP ! Block all exhaust heating , and insulate and interrupt thermal bridging to your intake. Insulate the carb from the manifold. Yes , it is worth it. Cool that carb. In the case of Cadillac , intake/carb pre-heating persisted inordinately , even after gasoline improved. In the case of my mid '20s Cadillacs with pressurized gas tanks , I have a certain advantage. Tom , I sure wish you a safe and enjoyable tour , full of happy events , and as few unpleasant ones as possible. I know you will report back to us.  - Carl

[Spinneyhill]

Let's have some more facts from GW Johnson's paper.

 

Gasoline has a latent heat of evaporation usually near 145-150 BTU/lbm, i.e. the amount of energy needed to vaporise the gasoline per pound mass. Ethanol has a latent heat of evaporation of 396 BTU/lbm, so gasoline is far easier to vaporise than ethanol.

 

The Reid Vapour Pressure of ethanol is about 2 psi. The RVP for automotive petrol is 9-15 psi, so it is far more volatile than ethanol.

 

OK, this might be it. He says " Sometimes (not always) the RVP of an E-10 blend can be higher than that of the base gasoline." but nothing else.

 

This paper says a 10% ethanol added to a 9.0 psi RVP gasoline gives a RVP of 10.0 psi. I also says the RVP must be limited from 1 May to 15 September to 9.0 in E15.

http://www.ethanolproducer.com/articles/8222/e15-cracking-the-rvp-nut

 

Carl, many makes had intake heating, e.g. 1930 Dodge Brothers 8, Studebakers of the '30s - my 1939 has a bi-metallic spring to operate it automatically. My Dodge's valve is not connected and must be closed - on cold days, I can get icing in the carb after a few minutes running and have to shut off for five minutes while it all warms up again.

 

 

 

Edited July 17, 2016 by Spinneyhill (see edit history)

[ply33]

1 hour ago, Spinneyhill said:

I think the next thing to find out, really, is whether the presence of ethanol causes any reduction in the boiling point of any fractions in the gasoline mixture. So far we know the lighter fractions boil at just about body heat. What about if we add ethanol?

 

 

Found this about ethanol in gasoline (on page 2):

 

Quote

Blending of ethanol into gasoline at 10 volume percent causes the RVP to increase by about 1 psi despite the fact that fuel grade ethanol has a lower vapor pressure than gasoline (see Figure 1). The low vapor pressure of fuel grade ethanol is caused by attractive forces between the ethanol molecules. The strongly electronegative oxygen atom in each ethanol molecule is attracted to the somewhat positive hydrogen atoms in other ethanol molecules. The attraction between ethanol molecules means that it has a stronger tendency to stay as a liquid and not vaporize into the more dispersed gaseous state. However, when blended into gasoline at relatively low concentrations the more numerous gasoline molecules disrupt the attractive forces between ethanol molecules and allow the ethanol to readily evaporate, raising the vapor pressure of the blend. Not surprisingly this increase in vapor pressure with ethanol is more marked with the lower RVP hydrocarbon blendstocks. This would be true with the addition of any component which raises vapor pressure, as the final pressure is a weighted average of the pressure contributions of all of the components. As ethanol content is increased above about 20% the vapor pressure increase becomes less, and above about 50% ethanol vapor pressure for the blend is less than that of the gasoline.

 

So basically 10% ethanol blends have a higher vapor pressure than "pure" gasoline and will thus vapor lock more readily. This seems to be confirmed by the antidotal evidence presented here by various people. And, if I am reading things correctly, higher RVP is allowed for summer blends which seems backwards to me with respect to what we want for our low pressure carburetor based fuel delivery systems.

Edited July 17, 2016 by ply33 (see edit history)

[Spinneyhill]

The Ethanol Producer article seems to imply the summer blend has a lower RVP requirement than at other times.

 

OK, I take back what I said above after further research. I have learnt a few things today!

Edited July 17, 2016 by Spinneyhill (see edit history)

[ply33]

8 minutes ago, Spinneyhill said:

The Ethanol Producer article seems to imply the summer blend has a lower RVP requirement than at other times.

 

OK, I take back what I said above after further research. I have learnt a few things today!

 

Yes. Re-reading and looking at some other sites, the RVP is required to be lower in summer. So I had it wrong above about that. But it does look like ethanol raises the RVP and they are typically allowed to have a 1 psi increase in RVP with 10% ethanol.

[Spinneyhill]

I found something, perhaps the Ethanol Producer magazine, that said they should have a 9.0 psi. RVP with 10% ethanol, but they got a waiver from the EPA way back in 1992 or so allowing 10 psi. Other reading shows it is hard to get it lower. California has (or had) a lower RVP requirement than other States?

 

This helps I think:

http://www.ethanolrfa.org/wp-content/uploads/2015/09/RVP-Effects-Memo_03_26_12_Final.pdf

Edited July 17, 2016 by Spinneyhill (see edit history)

[C Carl]

Wow ! Looks like this will eventually boil down to a definitive resolution. Don't let it drop. I know the vast amount of experience and high education level this has attracted can sort this out. Somebody certainly can referee this , maybe time to shake out the old boy network. Spinney' , here you see a couple of stages in my test bed mode. Aluminum foil sheets and "spit wads" made it remarkably easy to experiment. I don't know what the configuration of your carb/intake is. I ran into terrestrial carb ice in a Citroen 2 CV bouncing around Europe in the Winter almost 50 years ago. Being a pilot , I knew something about this. Rigged carb heat , (hot air intake) , and voila' , never stalled out again. I had bought the car in Denmark cheap from its frustrated owner , but it took me a while to realize what was happening. Got down to the French Riv. Life was great ! Way back on the somewhat labyrinthine back streets of Nice was a humble restaurant , Chez Jaquee' (sp. ?) . Large bowl of fresh mussels , 1/2 liter of wine , and , of course the most French of French Bread , abundant. 1.25 Francs. Two bits , U.S. at the time. Friendly Scandinavian ladies did not make any negative value judgements based on my primitive conveyance. What great outlooks on life they had. What fantastic , hopeful , innocent times ! Nice. We who are old now , are the luckiest generation who have/will ever live. Nice. Weep. - Carl

[tcslr]

Chevrolet - in 1932 - did have a intake heating butterfly valve - of which I disabled.  Like Mr ply33, I like to keep it stock BUT I am also a hypocrite as I did add a fuel pump and a momentary switch ( I like that and shamelessly steal good material where-ever I find it).  Usually I don't use it but sometimes.

as a ChE by Undergrad, and anecdotally, ethanol seems to get a bad rap.  Consider a bottle of liquor.  The ethanol doesn't seem to vaporize unlike say a can of gasoline.  Ethanol does separate in gasoline if permitted to sit for a long period of time.

 

[joe_padavano]

9 hours ago, F&J said:

 

If someone could design a very basic return system for the old engine driven mechanical pumps we have, why would that not work?  Those pumps are capable of a lot more flow than the tiny bit needed for running.  You'd need something to regulate the pressure for the carb, but let the pump run at max flow to dump the rest to the tank.  ?

 

GM already did this back in the 1960s.  All my Oldsmobiles with high performance engines came from the factory with fuel return.  The pump had an additional output barb that returned part of the fuel back to the tank through a separate return line.  There was a restriction in this outlet fitting so pressure to the carb was not reduced.  You can easily retrofit a system like this to a vehicle without fuel return, assuming you can run an additional return line back to the tank.  On the 1971 Olds 442 W-30 cars, there was a single outlet line from the pump and the fuel return actually came off the filter that was between the pump and the carb. This same concept could be used on any car with a carb and mechanical pump (or even an electric pump for that matter).

 

 

[carbking]

If the vehicle is new enough to have a pressure fuel system, we have been recommending the use of the return line for more than 30 years.

 

While it would lose points at a points show, it really reduces driveability issues in hot weather (notice I used the word "reduce", not "eliminate").

 

The easy way to do this is to disconnect the fuel line from the carburetor and install a three line filter with what is called a "vapor" line. The vapor line will be somewhat smaller than the fuel line. The three connections on the filter will be "in" (from the pump), "out" (to the carburetor), and "vapor" (return to the fuel tank). The return line, FOR BEST RESULTS, SHOULD run ALL the way to dump into the tank. A couple of places in the tank would be the filler neck, or drop the tank, remove a bolt from the sending unit, drill a hole lengthwise through the bolt, and sweat in a piece of tubing. The bolt can then be reinstalled, and the line attached to the tubing. Just running the line back to the input side of the pump does NOT help very much.

 

The return line will eliminate vapor lock issues, and will also reduce, but not totally eliminate hot soak issues (which are often mis-diagnosed as vapor lock).

 

And while ethanol can make the issue worse, ethanol is not the major cause. There are other aromatics in todays fuel which, for this issue, are worse than ethanol.

 

EDIT: - Joe posted much the same while I was typing. My "source" for this idea was basically to look at what the car manufacturers did in the 1960's when the engine compartments became "smaller" due to lowered hood and larger engines. As a good friend that posts on another forum is so fond of saying "engineers do things for a reason"!

 

Jon.

Edited July 17, 2016 by carbking (see edit history)

[DavidMc]

Joe,

No problem plumbing a return line back the tank but how do you determine the size for the restriction orifice needed in that line to ensure that the return flow never starves the feed to the engine?    The attachment to post #13  deals with this but its not simple.

 

 I have learnt a lot form the information being exchanged here and the attachment from Spininghill regarding the effect of ethanol on RVP is particularly interesting and surprising. 

 

 

[F&J]

24 minutes ago, joe_padavano said:

GM already did this back in the 1960s.  All my Oldsmobiles with high performance engines came from the factory with fuel return.  The pump had an additional output barb that returned part of the fuel back to the tank through a separate return line.

 

14 minutes ago, carbking said:

The return line will eliminate vapor lock issues,

Yes, I have seen the OEM GM return line at the pump, but I have another question:   The GM return barb/hose is very small, so my question is, does even a tiny return work to eliminate lock, even with constantly changing and newer fuel blends?

 

It sounds like both of you suggest that "any size" of a return will get rid of the trapped pressure from a vapor lock?

 

 

[carbking]

F & J - I have not done any research on how SMALL a line may be used. Typically, when using the 3 line filter, the "vapor" line will be one "size" smaller than the fuel line. Examples:

 

3/8 inch fuel line - 5/16 inch (sometimes 1/4) vapor line

5/16 inch fuel line - 1/4 inch vapor line.

 

The idea is to keep the fuel moving through the fuel pump, not allowing it to sit on the low pressure side of the pump, where heat can cause bubbles in the liquid.

 

Jon.

[F&J]

30 minutes ago, carbking said:

The idea is to keep the fuel moving through the fuel pump, not allowing it to sit on the low pressure side of the pump, where heat can cause bubbles in the liquid.

Here is a cutaway of a Bosch fuel injection pressure regulator that uses a "high flow return capability"

 

I have this type on a factory stock older daily driver car.  I do have a fuel pressure gauge at the motor that I added.   I have adjusted this valve, but because it was designed for 10X the pressure of a carbureted engine, the spring is just too strong to go much lower than 25? PSI.  But, it has a huge flow capability on the return hose which could compensate for the rare occasion of a incredibly hot day.( I'm taking about a massive fuel boil, that is so intense, that a pre-drilled orifice on a homemade return system, would be overtaxed?)

 

I wonder if a very weak spring could be used to get it to work at 2 to 3 PSI?   (they are crimped sealed, not made to be taken apart, though).  If not, maybe a web search for some type of aftermarket "3 hose regulator" for racing engines with carbureted engine?

[F&J]

Take a minute to view this page on the link below...

 

I think there is a good chance of finding a high quality "return type" regulator somewhere. 

 

Read the specs text; it says it can be used on high pressure fuel injected, but "also can be used when converting to carbs".   But it's lowest setting is 5 PSI, and I think we'd need 2 or 3?   Any thoughts on 5PSI to these early carbs where 5 might lift the float?

 

https://www.dellorto.co.uk/shop/car-accessories/fuel-pumps-regulators-accessories/malpassi-turbo-fuel-pressure-regulator/

[joe_padavano]

1 hour ago, carbking said:

The easy way to do this is to disconnect the fuel line from the carburetor and install a three line filter with what is called a "vapor" line.

 

As Olds did on the 1971 W-30 cars with AC filter GF-432.  Note the small barb for the return line, which is 1/4".  The filter has a restriction built into the barb to prevent loss of pressure to the carb.

 

By the way, that is NOT a "vapor" line, it is a fuel return line and carries liquid fuel back to the tank.  These cars had a separate vapor line from the tank vents that ran to the charcoal canister for emissions control reasons unrelated to the fuel return issue.

 

 

Edited July 17, 2016 by joe_padavano
clarification (see edit history)

[F&J]

If my 32 Nash with engine-driven mechanical pump, was heading for a trip through the desert..     Here is what I would try:

 

Use a 8-10 PSI full time electric booster pump at the rear near the tank.   Then that pumps feeds through the stock pump. 

 

The Malpassi 5 PSI "return type" regulator is in the line between the stock pump and the carb.

 

Then add a 2 hose small inline low pressure regulator between the output of the Malpassi and the carb inlet. These can be set to 2 or 3PSI as I recall

 

The 8-10 PSI pump insures a constant flow of cooling fuel through the stock pump, if using the Malpassi regulator upstream.  Then the small 2 hose regulator won't be overtaxed by fuel boil, or the 8-10 pump.

 

Right now, my Nash has an electric booster pump that feeds through the stock Nash pump.  I use the pump to prime the carb after sitting for a week, then shut it off and the mechanical pump then runs the engine.  In other words, the stock pump does not need any modifications to have an electric pump feeding "through it"

 

 

[carbking]

Joe is of course quite correct in that the line is not a true "vapor" line, which is why I placed the word "vapor" in quotes. However, most parts house employees will call it a vapor line (incorrectly) and not know about a "return" line. Sometimes, when trying to purchase an item, better to use the incorrect terminology in common useage rather than confuse the parts man

 

Joe mentioning the charcoal cannisters brings us another misunderstood issue. Lots of individuals removed these cannisters in the mistaken idea that doing so would aid both performance and economy......it doesn't!

 

The emissions laws were very inconsistant in the 1970's and early 1980's. Some of the "heavy duty" trucks carried no or very few emissions requirements into the early 1980's. My Dad had a motor home which was built, obviously, on a truck chassis, and had no cannisters. The motor home had a 75 gallon tank MOUNTED BETWEEN THE TWIN MUFFLERS! Even though the tank was well vented, the vent could not prevent pressure from building up in the tank. Quite dangerous when removing the fuel cap for refilling when the engine was hot. Since there was no factory installation to go on, I used three cannisters from light trucks with 25 gallon tanks, which solved the issue and also slightly improved fuel economy.

 

Jon.

[JACK M]

The bottle of liquor evaporates quickly around here.

Not me, but those idiot aquaintences.

[joe_padavano]

1 hour ago, carbking said:

Joe is of course quite correct in that the line is not a true "vapor" line, which is why I placed the word "vapor" in quotes. However, most parts house employees will call it a vapor line (incorrectly) and not know about a "return" line. Sometimes, when trying to purchase an item, better to use the incorrect terminology in common useage rather than confuse the parts man

 

Amen!  This is why I just order by P/N and don't rely on the person behind the counter anymore.  Frankly, since parts stores around here rarely have what I need in stock, It's much easier to just order on line.  Parts show up on my doorstep rather than my needing to make two trips to the parts store and deal with incompetence. Shipping cost is usually about the same as local sales tax anyway.  Heavy or oversize parts (rotors, calipers, exhaust pipes) are about the only items that make sense to buy locally to avoid excessive shipping costs.

[ply33]

9 minutes ago, joe_padavano said:

 

Amen!  This is why I just order by P/N and don't rely on the person behind the counter anymore.  Frankly, since parts stores around here rarely have what I need in stock, It's much easier to just order on line.  Parts show up on my doorstep rather than my needing to make two trips to the parts store and deal with incompetence. Shipping cost is usually about the same as local sales tax anyway.  Heavy or oversize parts (rotors, calipers, exhaust pipes) are about the only items that make sense to buy locally to avoid excessive shipping costs.

 

Off topic, but my preference is to keep as many local businesses in business as possible. But I don't like two trips to a store to get an item either.

 

Fortunately I have the modern invention by either Elisha Gray and/or Alexander Bell (depending on who you believe) called a telephone. I can use the telephone to assure the parts I want are available or, if not at in stock, can be delivered to the store from their warehouse sometimes that afternoon and usually no later than the next morning. I find it generally faster to get parts and I get the option of looking at them and deciding if they are correct before I pay and take delivery. Not sure if I am paying extra for this type of quick and personalized service, but it is worth it to me.

[DavidMc]

Jon,

 

Would you care to elaborate on what you mean by " heat soak" issues as opposed to vapor lock .  I guess you are talking about what happens when the car is stopped after a hot run and will not restart until it cools, due to what I would have called vapor lock.  I am interested to know how it differs from vapor lock.

 

It is my understanding of what we are all talking about here is fuel that cannot be pumped due to the formation of vapor bubbles in the fuel lines.   If vapor is forming in the carburetor float bowl then the situation is different and the venturi probably draws off either pure vapor ( with insufficient energy to keep the engine running) or a mixture of liquid and vapor causing that jerking effect that happens some time.

 

 

 

 

[cahartley]

8 hours ago, ply33 said:

 

Off topic, but my preference is to keep as many local businesses in business as possible. But I don't like two trips to a store to get an item either.

 

I can use the telephone to assure the parts I want are available or, if not at in stock, can be delivered to the store from their warehouse sometimes that afternoon and usually no later than the next morning. I find it generally faster to get parts and I get the option of looking at them and deciding if they are correct before I pay and take delivery. Not sure if I am paying extra for this type of quick and personalized service, but it is worth it to me.

 

No kidding.

I learned (but nearly long enough ago) to not trust web results which SAY an item is in stock at a particular store only to go and come home with nothing....... 

A lot of parts people are no better than their computer but I can't fault THEM for not knowing every XYZ for every car on the planet so I, too, search by part number AND verify it well as I can.

THEN I make the call to verify it's IN STOCK and ask them to hold it for me as I'll be in in X minutes.

No more driving 35 or more miles for nothing....... 

Edited July 18, 2016 by cahartley (see edit history)