vapor lock additives or ideas

[cahartley]

3 hours ago, DavidMc said:

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.

 

Good question Jon.

I understand "heat soak" to cause fuel in the carburetor to percolate thereby causing a flooded situation.

I experienced heat soak with my '65 I6 200 engine Mustang when the heater core was plugged so the coolant spacer between the carb and manifold wasn't doing its job.

It was hard starting hot and diesel a lot when shut off when hot.

Once I restored flow through the heater and spacer my problems were over.

I've read a LOT about these issues but still don't truly understand vapor lock....... 

 

 

 

 

 

[ply33]

4 minutes ago, cahartley said:

Good question Jon.

I understand "heat soak" to cause fuel in the carburetor to percolate thereby causing a flooded situation.

I experienced heat soak with my '65 I6 200 engine Mustang when the heater core was plugged so the coolant spacer between the carb and manifold wasn't doing its job.

It was hard starting hot and diesel a lot when shut off when hot.

Once I restored flow through the heater and spacer my problems were over.

I've read a LOT about these issues but still don't truly understand vapor lock....... 

 

As I understand it there are at least two heat related failure modes on carburetor equipped cars:

 

1. "Vapor Lock": Pumping action failure due to vaporization of the fuel in the pump. Pump is designed to move liquid, not gas, so it becomes ineffectual at best when this happens. This seems to be the problem I occasionally face and my cure is simply pouring some cool water on the fuel pump. I often carry drinking water in summer, so I am carrying the "tool kit" needed to get back on the road but it is an annoyance.

 

2. "Heat Soak": A hot restart issue caused by fuel expanding or boiling in the carburetor float bowel when parked. In this case the fuel makes its way into the manifold causing an over rich mixture. I haven't seemed to have had this issue, but have heard of many others that have. Apparently you will have a better chance of starting the car if you hold the accelerator down (do not pump) to get more air through the engine to clear it. One suggestion for fixing this on the simple single barrel carburetor on my car is to adjust the float to a bit lower than factory spec. Other suggestions include insulating the carburetor better from engine, especially exhaust manifold heat.

[cahartley]

Interesting you mentioned the float thing as just 3 days ago I got weary of the gassy smell in my Mustang (Autolite 1100 carbs are infamous for that), popped the top off the carb and raised the float 1/8", which is quite a bit, but the fuel left in the bowl suggested it would stand the change.

It did.

The gassy odor is now nearly nonexistent and the engine performs the same.

Maybe the mileage will improve too........I hope........

[hwellens]

7 hours ago, cahartley said:

Interesting you mentioned the float thing as just 3 days ago I got weary of the gassy smell in my Mustang (Autolite 1100 carbs are infamous for that), popped the top off the carb and raised the float 1/8", which is quite a bit, but the fuel left in the bowl suggested it would stand the change.

It did.

The gassy odor is now nearly nonexistent and the engine performs the same.

Maybe the mileage will improve too........I hope........

You raised the float which puts the gas in the carb at a higher level and that helped?

[carbking]

Ply33's answer is very good. Adding a wee bit:

 

(1) Vapor lock - air bubbles form on the inlet side of the fuel pump (low pressure). While the pump will actually pump vapor, it was not designed to do so, and does so very poorly. So the pump is said to be vapor-locked, and no or very little fuel goes through the pump to the carburetor.

 

(2) Heat soak - percolation can certainly occur in the carburetor, generally after engine shutdown, but it also can occur during long periods of idling in extremely hot weather.

 

But carburetors have a variety of vents: bowl vents, idle air bleeds, main air bleeds, accelerator pump vents, etc. Since the vapor is lighter than the fuel, it will be on top of the fuel in whatever portion of the carburetor (bowl, accelerator pump cylinder, idle well, main well, etc). As the volume is increased when a liquid is transformed into a vapor, some pressure will result (50 years ago I could tell you who stated this law of physics, but cannot remember without looking, and hopefully he/she will forgive me for not citing his/her name  ). This pressure will be relieved through a vent, generally into the air cleaner (the accelerator pump vent is a different animal and will be discussed below). During a period when the engine is not running, the air cleaner can become saturated with fuel vapors. This will explain why a very hot engine will sometimes start right up, and then stall after a few seconds and be hard to start. If the throttle plate(s) were closed, the mixture in the manifold would not be oversaturated and the engine would start, but then the vapors in the air cleaner would be significant in relation to the fuel delivered by the carburetor, and create a mixture so rich that the engine could not burn this mixture AT IDLE. The solution: if your engine is prone to this issue, run the engine at a fast idle  for 15~20 seconds after it has been started when hot. The higher engine speed will allow the oversaturated mixture to burn, and thus clear the air cleaner of the vapors. Likewise, if the engine seems to stumble or misfire when idling in very hot temperatures, run the engine at a higher idle, or blip the throttle occasionally to keep it clear. This condition is also referred to as "loading up".

 

The accelerator pump vent - on some vehicles, the operator will occasionally notice that the accerator pump will pump little or no fuel ON THE FIRST SHOT! If I had a nickel for every good accelerator pump that had been replaced for this reason, I could buy the island of Hawaii and retire  ! The problem can be, and often is, percolation in the pump cylinder. Think of the construction of the accelerator pump circuit. We have a cylinder, normally filled with fuel, some form of an inlet to the bowl which is generally a valve, but on newer cheaper units, a slot in the upper portion of the cylinder, a passage to a pump discharge valve then to the pump jet, and the accelerator pump. Under very hot conditions, vapor bubbles can form in the pump cylinder. This creates pressure in the pump cylinder, can overcome the designed closed pressure of the discharge valve, thus causing a small amount of fuel to leak past the discharge valve through the pump jet into the engine. Over time, the entire fuel volume of the pump cylinder may be depleted, meaning that on the first stroke of the pump there is nothing to pump and thus no squirt into the engine. When the pump is lifted for the second squirt, the inlet fills the cylinder, and the pump works. This is NOT new! The issue was recognized by the carburetor manufacturers in the 1930's, and at least two methods were devised to attempt to deal with the issue. The first and least expensive method was to increase the mass of the discharge valve (or use a stronger spring, if a spring-loaded valve) thus attempting to combat the pressure in the pump cylinder. The second method was more successful. A check valve was incorporated in the the accelerator pump. This consists of a tiny ball in a chamber with a vent at the top of the chamber and an inlet to the pump cylinder below the ball. The mass of the ball is designed to be significantly less than the mass of the discharge check valve, so that bubbles in the the pump cylinder will lift the ball, discharge into the vent passage, and discharge through the vent into the carburetor bowl, where they can then be vented out through the bowl vent. When the accelerator pump is engaged, the mass of the ball will cause it to rise in the chamber, closing the vent at the top of the chamber, and allowing the pump to function normally, even on the first squirt.

 

EDIT: when starting an engine susceptable to these issues, try the methods in the link below:

 

http://www.thecarburetorshop.com/Troubleshooting.htm#Hardstartcold

 

Jon.

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

[JACK M]

7 hours ago, hwellens said:

You raised the float which puts the gas in the carb at a higher level and that helped?

 

Maybe more pressure on the needle valve ?

Or he is holding the float assy. upside down while adjusting. If it worked all is good.

[cahartley]

7 hours ago, hwellens said:

You raised the float which puts the gas in the carb at a higher level and that helped?

 

I raised the float to put LESS gas in the carb.

[joe_padavano]

32 minutes ago, cahartley said:

 

I raised the float to put LESS gas in the carb.

 

Unfortunately, that is not what you got.  Raising the float measurement raises the level of fuel in the float bowl.  Lowering the float lowers the level of fuel. A carb works just like the float in a toilet tank.

 

If, however, your carb hangs the float from the underside of the air horn, and you adjust the float level while holding the air horn upside down, then yes, "raising" the float lowers the fuel level. Of course, once you turn it over and install that air horn back on the carb, you see that you actually LOWERED the float relative to the engine (and relative to gravity).

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

[cahartley]

No I did NOT.

I RAISED the float height with the carb top upside down.

 

[JACK M]

Your description is confusing.

It would seem to me that you are describing a lowered float position. As Joe said, relative to the engine and gravity.

[JWLawrence]

I had good experience using  5% diesel in the gasoline. Also, vapor locking occurs in the unpressurized part of the fuel system. That is why an electric fuel pump can overcome the vapor locking. Protecting the fuel lines and parts in these unpressurized  areas may help.

 

(o[]o)

 

[tcslr]

Well, an update of conditions and observations.  Conditions were tougher - daytime temperatures were 90 to about 93 with humidity varying.  The tour did not have excessive long runs ( >30 miles at a clip) and only several fairly long hills ( 5% grade for about 1 mile).

On day one after a long climb, the Chevy started to vapor lock and the use of the electric fuel fixed the solution but as soon as I cleared the vapor locking, I then turned off the pump..  I did have some increased temperature but not severe over-heating.

That afternoon I added about a 5% addition of diesel -  ( temps about 92), I did have some difficulty starting the hot engine ' hot start' then carburetor vaporization?

After diesel addition, and the next morning especially, the car was a little harder to start.  I have NOT yet examined spark plugs.

 

Day 2 - higher temps by a degree and one instance of vapor lock - with ~5% diesel AND cleared by use of electric pump. Strange.  Continued harder starting or rather slower starting - typically, it fires on the first few revolutions of starter.  Increased diesel to ~7%. 

 

After ~7%, starting was a little 'harder'..... So decided next iteration was back to 5%.  During the heat of the day, the car was hard to start - it would fire on a cylinder or two then require chiocking to get it to start and it was almost always irregular - not all cylinders firing then cleared to all cylinders firing in 10-12 seconds. 

 

Observed another car using 10% diesel - and significant exhaust smoke.  Friends told me they did not see smoke at any time from 5-7 to maybe 3ish%.

 

By day four, I was really tapering off the diesel addition shooting for 3-4ish% I just was getting frustrated with the harder starting.

 

Additional measures after any run then tour stop was to open hood to aid cooling AND pour a little water on the fuel pump.  Starting was always hard so I started to pour a little water on the fuel line to carburetor ( I have it insulated and assumed that the water-soaking would result in transpirational cooling - alas, still hard start).  Almost AWLAYS needed to choke it AND use about 1/4 foot throttle to start.  Almost ALWAYS fired irregularly but cleared after 7-10 seconds to consistent cylinder firing.  Then idled fine and ran OK.  With the higher percentage diesel in the morning with a cool engine, it seemed to have a periodic misfire that disappeared after about 5 minutes, medium to high throttle and then warm engine.

 

Some suggestions from some folks on the tour: change the line from copper to SS.  polish the copper entering the pump ( better reflection? lower emissivity?), add more insulation, go to 10% diesel.

 

Use of the electric pump all the time seems to flood the engine after I stop ( especially after running for some time)  I can hear the electric pump running and then it sounds like ( after say 7 seconds) to start to dead-head.

 

I think the car needs re-tuned to run the diesel addition - but how?.  It generally does seem to help but the slower starting is a problem and confusing - any thoughts?

 

 

[F&J]

13 minutes ago, tcslr said:

think the car needs re-tuned to run the diesel addition - but how?.  It generally does seem to help but the slower starting is a problem and confusing - any thoughts?

This is no help to you, but the antique tractors in depression, started on gas, then switched to all diesel, then to shut down at days end, it was switched to all gas for a few minutes.

[DavidMc]

I have found kerosene to be more effective in avoiding vapor lock and it does not seem to make any difference to performance or starting.  The main problem with kerosene is that it is only available (here in Australia) in 5 litre bottles so its best used with a low fuel tank in order to get about 10%.  I tried diesel on a particularly hot day when vapor lock was a serious problem it made no difference to the vapor lock but I do not recall any starting issues.  I have always used kerosene since then.

[DavidAU]

"The main problem with kerosene is that it is only available (here in Australia) in 5 litre bottles"

 

Bunnings sell it in 1 litre bottles

[DavidMc]

I mean't that 5l was the largest readily available,  Bulk from the service station would be better .  We had a BP nearby that had a kerosene bowser years ago, that was ideal. 

[JACK M]

Same thing as lamp oil.

Maybe Wal-Mart or the likes.