2023 BCA National Meet, Spokane Washington, July 11-15 2023

[maxinvan]

I was wondering about the diesel additive in the petrol, but you answered that question, telling us you added about one gal to 12 gals petrol, I note that although you were uncertain as to it’s effectiveness you kept adding it, therefore the conclusion I draw is that it did not adversely affect the cars performance and you obviously felt it may be helping.

[Larry Schramm]

I was on a tour a couple of weeks ago in Alabama with a southern group and I was told by members of that group in hot conditions that 10% diesel to gas will help vapor lock. 

Edited July 30, 2023 by Larry Schramm (see edit history)

[old-tank]

3 hours ago, Larry Schramm said:

I was on a tour a couple of weeks ago in Alabama with a southern group and I was told by members of that group in hot conditions that 10% diesel to gas will help vapor lock. 

Nope.  You still have 90% volatile gas with essentially no effect.  Vapor lock occurs on the suction side of a fuel pump.  The only things that work is a pump near the tank that will push fuel and any vapor; a return system; copious insulation or rerouting the fuel line.

[Larry Schramm]

28 minutes ago, old-tank said:

Nope.  You still have 90% volatile gas with essentially no effect.  Vapor lock occurs on the suction side of a fuel pump.  The only things that work is a pump near the tank that will push fuel and any vapor; a return system; copious insulation or rerouting the fuel line.

 

All of my cars and trucks up to 1917 use gravity feed for the fuel.  After that the next two vehicles have a Stewart-Warner vacuum system.

Edited July 30, 2023 by Larry Schramm (see edit history)

[NTX5467]

5 hours ago, Larry Schramm said:

I was on a tour a couple of weeks ago in Alabama with a southern group and I was told by members of that group in hot conditions that 10% diesel to gas will help vapor lock. 

Just curious if they were using current "pump" diesel or "off-road" diesel with a bit more sulphur in it?

 

NTX5467

[Larry Schramm]

1 hour ago, NTX5467 said:

Just curious if they were using current "pump" diesel or "off-road" diesel with a bit more sulphur in it?

 

NTX5467

 

Pump diesel.  Go to the same pump with two nozzles.  Put in 1 gal diesel and fill up the tank with the gas.   Most of the cars of that era have about a 10 gallon tank.

Edited July 31, 2023 by Larry Schramm (see edit history)

[Bill - 29 Buick]

When I get time to work open the car - probably in Sept. after getting my Cord ready for Auburn, I'm going to try one of these filters with a vapor separator and see if that helps.  Of course, it will be cooler then but I may get some inkling of what's going to happen next summer, in the heat.

 

Billy

 

[38Buick 80C]

48 minutes ago, Bill - 29 Buick said:

When I get time to work open the car - probably in Sept. after getting my Cord ready for Auburn, I'm going to try one of these filters with a vapor separator and see if that helps.  Of course, it will be cooler then but I may get some inkling of what's going to happen next summer, in the heat.

 

Billy

 

?

So curious how is that supposed to work (I mean the plumbing of it, not the technicalities of the vapor separation itself). The return tube goes where?

[Larry Schramm]

1 hour ago, Bill - 29 Buick said:

When I get time to work open the car - probably in Sept. after getting my Cord ready for Auburn, I'm going to try one of these filters with a vapor separator and see if that helps.  Of course, it will be cooler then but I may get some inkling of what's going to happen next summer, in the heat.

 

Billy

 

 

I would think that the unit would be used with an electric fuel pump.  Does the return line go back to the fuel tank?

[B Jake Moran]

Yeah that’s a puzzler.  It has to be returned somewhere. I would think a person would have another modification at the gas tank.  

[Bill - 29 Buick]

2 hours ago, 38Buick 80C said:

So curious how is that supposed to work (I mean the plumbing of it, not the technicalities of the vapor separation itself). The return tube goes where?

The person who told me about it said the third tube should be facing up and it can be connected to the fuel line behind the fuel pump (ie. between the gas tank and fuel pump).  Beauty is that you don't have to go all the way back to the tank - it can be just a few inches from the fuel pump.

 

Bill

[Bloo]

I'm not sure it is really like what is shown in the cutaway. I have used these to combat vapor lock, and it helps a little but not a lot. Buick and Chrysler used forms of this. In addition to the one pictured, there is also a version with the third port parallel to the fuel ports, and there is also a 3/4 sized one for Chrysler K-cars. These are for a very specific problem, and @carbking has an explanation posted on his webiste somewhere, but I can never find my way back to it so I can't link it here. I'll get back to that specific problem in a minute.

 

I have never heard that one of these filters had to be in a specific orientation, and I don't really believe it does. When I used them I believed I was separating vapor, and tried to get the return (small) port up high in the system, but that doesn't really make any sense. Also the factory systems usually didn't have the filter at a high point. If you are "vapor locked", and the engine is not running because it has no fuel, the float valve is wide open. Vapor can already escape. No, the important part of the 3 port filter is that .062" jet and the return line, which on most factory installations I have seen goes all the way back to the gas tank and dumps fuel there. To duplicate that you need an extra vent port on the gas tank.

 

You can use this with a mechanical fuel pump, at least if the pump is big enough, and in many cases it is. You just have to be able to supply everything the engine needs plus the .062" "leak". Many factory installations used a mechanical fuel pump. I don't believe it would be practical to use this with a vacuum tank, but I have not tried. Some fuel is always circulating, and the mechanical fuel pump diaphragm always moves a little, rather than staying stationary during periods when the float valve is closed. It may carry some heat out of the fuel pump and back to the tank. This is why I believe it helps a little (not a lot). It does not give you the huge benefit you would expect if you were "letting the vapor escape" (like I thought many years ago).

 

You can also use this with an electric pump, or with an electric pump pushing through the diaphragm pump. That last version is not recommended if you are going to leave the electric pump running all the time, but I have done it when using a brand new diaphragm and a rear-mounted electric pump. It helps a little more, because if fuel boils anywhere, such as in the line under the car, the pump keeps forcing more fuel in and any vapor is forced out the .062 jet into the return line, or at least that is what I was hoping for. Did this solve the problem? No, but it helped a little bit more than the 3 port filter by itself. As I recall it gained me about 5 degrees F in ambient temperature before the car would stop running completely.

 

The real reason those filters exist is to solve a specific hot-soak problem. On Buicks, they are typically used on air conditioned cars. When a mechanical fuel pump boils in a hot soak situation (you just shut the car off on a really hot day), and the carburetor is full, and the float valve is shut, the pressure in the fuel pump rises dramatically. The pressure cannot escape back to the tank because of the inlet check valve in the pump, so it overpowers the closed float valve, opening it, and blows whatever liguid gas is in the fuel line and filter into the carburetor bowl. The fuel in the carburetor then runs over through any hole it can find (usually the main discharge tubes) and floods the engine.

 

Edited August 1, 2023 by Bloo (see edit history)

[KAD36]

When first seeing that filter my assumption was it went after the pump and the 3rd line would go back to the filler neck area to not introduce vapor into the suction line.  Having trouble visualizing how it works tied in line just ahead of the pump if I’m understanding the thread properly….

[EmTee]

I agree; my understanding is that this filter mounts between the pump outlet and the carburetor inlet.  When the carburetor inlet needle valve is closed (fuel bowl full) the small nipple connects to a line that runs back to the top of the fuel tank.  This allows cool fuel from the tank to circulate in the fuel line to the pump (suction side) rather than simply dead-ending the flow, allowing underhood heat to soak the gas held in the line while the needle is closed.

[KAD36]

22 minutes ago, EmTee said:

This allows cool fuel from the tank to circulate in the fuel line to the pump (suction side)

But if there’s vapor in that line ( going by the vapor chamber call out in the cutaway) and it’s reintroduced into the suction line doesn’t that defeat the purpose?  That’s why I thought it had to go back to the tank.

[EmTee]

Yes, the small nipple outlet on the filter goes back to the tank.  If working as designed, this setup should prevent heating the fuel in the suction line to the point where vapor lock occurs.  The check valve in the fuel pump keeps the pump from sucking air through that 3rd pipe, since the filter is on the pump outlet.

[Bloo]

I have heard of people looping these back to the pump intake, and even have heard of a factory setup like that but can not verify that it existed. I can't imagine how that would work. I'm pretty sure it would make matters worse. One of the most important things you can do on a mechanical fuel pump system is to make absolutely sure there are NO LEAKS AT ALL in the suction line from the fuel pump intake all the way to the tip of the fuel pickup at the bottom of the tank. When the gas tank is out, I use a mityvac to verify the integrity of the steel line. I also verify the fuel pickup line in the sender or tank. A steel line inside a tank can have rust pinholes. The copper pickup lines GM used are often cracked. If there is a rubber hose connecting the tank to the steel line on the chassis, I replace it with a lined one like SAE 30R9. Leaks on the suction side do not usually show by leaking fuel on the ground, even when the car is not running. I am not sure how that can be, but it just is. Looping the filter we have been discussing in this thread back to the suction line would effectively leave you a .062" hole in the suction line! In my opinion, this filter has to have it's own line all the way back to the tank.

 

The faster you can recover from "true" vapor lock, which as I understand it means boiling in the suction line under the car. the better. An engine with a carburetor will keep running as long as there is gas in the carburetor, perhaps badly if the level is low or the gas is boiling in the carburetor, but it will run. As long as the engine is still running there is a good chance for recovery, maybe even before you realize anything is wrong.

 

Also of very high importance are the check valves in the fuel pump. They should hold vacuum. None are absolutely perfect, but they should hold vacuum for quite a few seconds dry, and definitely not leak down instantly. It was an unwritten rule in the old days to NEVER change or mess with a properly sealing check valve when overhauling a mechanical fuel pump. In my opinion, it is still true of the phenolic check valves. You can change the springs under the phenolic if you want but I probably wouldn't even do that. The problem today is if there is any rubber or elastomer in the valves, then you would have to put the new ones in for ethanol compatibility or to combat rubber rot. They might not seal well until they break in. Always check and nitpick them until they seal properly if there is any way to do so. I'm guessing it took a month or two back then for break in, and as little as some people drive these cars today, it might take 10 or 20 years. I don't have a good answer for what to do there.

 

If the check valves have to be wet with fuel to seal, I think you are going to have a bad time on hot days. If the fuel pump has boiled dry when the car was parked hot, there won't be any gas to help them seal. If there's no gas in the carb to get the engine started either, you might crank until the battery is dead. Most mechanical fuel pumps are driven by the camshaft. Camshafts run at half crankshaft speed, and most fuel pump cams have one lobe. It follows then that it takes 2 turns of the crank for one stroke of the fuel pump. For reference, that's one whole run through the firing order, or 6 starter "chugs" on a 6 cylinder engine before you even start to get a second fuel pump stroke. How long does that take? How long did it take for those check valves in the pump to leak down when you checked them with vacuum? Is the suction from the first stroke already gone when the fuel pump makes a second stroke? It is going to have a really hard time lifting fuel all the way from the tank if so. Do you have an .062" hole in your suction line?

 

Edited August 3, 2023 by Bloo (see edit history)

[NTX5467]

When I first read of the use of a "vapor separator" in place of a normal inline fuel filter, in an effort to decrease vapor lock in Bill's '29, I thought "That's interesting".  When I read further, to the issue of putting the vapor line back into the main fuel supply line, on the tank side of the pump, that seemed as if it might be a "good hack", as it would not require any significant modification to the existing fuel system.  BUT . . .  if what was actually going back to the pre-pump location was vapor, then putting vapor into a suction situation would only increase the vapor there, due to the suction.  Not desired.

 

Chrysler and GM both used vapor separators in some of their factory fuel systems.  With the vapor line generally horizontal or vertical (on the top of a vertically-oriented fuel filter.  In either case, the vapor/return fuel went back to the fuel tank itself.  In reality, an inexpensive way to get "return fuel" using an existing fuel pump.  Later, GM started to use "3-line" fuel pumps in some applications with an in-carburetor fuel filter.

 

In about the 1984-1985 model years, we started to see "hot fuel handling" complaints on 305 4bbl Monte Carlos and Camaros.  GM had issued a TSB and related "kit" of parts to install or change location of.  I thought this peculiar, UNTIL I looked under the hood of an affected Camaro.  THEN it all made sense!  Due to how the underhood-area plumbinb was (hvac, hoses, etc.), NO air was reaching the QJet carb.  No way, no how.  One owner wrote to a car magazine stating that the dealer had done the TSB with little to no improvement.  End result was that with the very small float bowl volume of a QJet, as soon as the fuel enters, it is consumed by the carb jets into the engine.  With little in reserve, as soon as that supply is depleted (through heavy throttle movements and such), the engine becomes unresponsive, temporarily.

 

A few years later, these TSBs would be obsoleted by the 1987 EFI/TBI fuel eystems.  The engineeers knew this back then, so no real desire to spend lots of money on re-designs which would only be beneficial during certain times of the year and certain conditions.

 

The use of diesel fuel is a means of decreasing the volatility of the current fuels, I suspect.  Obviously, "octane" is not a consideration for these older, low-octane requirement motors.

 

To me, any exposed steel-type fuel lines probably should be polished with 600-grit red ScotchBrite to increase their heat reflectivity, then clear-coated for durability.  Under the car, out of sight to a casual observer, then some reflective/insulative "wrap"/heat shielding tubes can protect the fuel lines from heat radiated by the roadways and added to by under car heat from the engine compartment.  At the back, something of a silver mylar plastic heat shield for the fuel tank, while the vehicle is being driven, which can be easily removed for judging purposes?  I suspect that more modern vehicles would be a bit more involved to do this on than an earlier model vehicle.  Key thing would be to decrease the amount of heat absorbed by the fuel (above ambient temperatures) between the gas cap and the carburetor, as much as possible.  Remember the "clothes pins on the fuel line" to help decrease vapor lock tendencies??

 

Back in about 1988 or so, a motor home appeared in our service department one summer afternoon.  Complaint was "No power.  Top speed down hill of about 55mph".  One of our better techs drew the job.  He went for a ride with the customer and his family.  Although it was a normal Chevy 454 powertrain, it had no power, yet everything checked "normal".  On a whim, the tech got a pair or vice grips and clamped-off the return line from the fuel pump.  Suddenly the MH cruised at 70mph, with ease, as it should have.  He came into the parts counter wanting a carb jet.  He told me what he was going to do and I managed to fine an old carb jet in a dusty drawer parts bin.  He installed that jet in the return line from the pump.  Issue solved!  As it turned out, the customer had left MIdland, TX that morning on their way to Dallas.  Only being able to run 50mph on a Texas Interstate was not good or enjoyable.  They had stopped at any Chevy dealer of any size, plus some motor home specialists, about five times before they got to us.  An aux pusher electric pump had been installed at the tank, with little improvement.  No other shop had found anything significant.  Then our guy had a thought that perhaps there was too much return fuel, and addressed that possibility, which worked.  By the time they got to us, it was later in the afternoon . . . a long day for them to go several hundred miles.  When they left, they were smiling!

 

The older cars (as I recall from back then) sometimes had vapor lock issues when they were new or "just used cars".  Just a part of cross-country travel in the vacation season of the year, back then.  Whatever issues there were back then have been amplified by hotter vacation seasons (!!!!) and flakier, higher-volatility fuels.  Nobody wants to be sitting on the side of the road, with an inoperable engine due to vapor lock issues, now or in earlier times.

 

Just some thoughts,

NTX5467

Edited August 4, 2023 by NTX5467 (see edit history)