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Veteran
Posts: 101
Location: Palm Beach County Florida | I have been plagued with vapor lock ever since I had the Vintage Air system installed last year on my Poly engine CRL
I replaced the four-blade fan with a six blade.
I had a Walbro electric fuel pump installed.
I insulated the under hood fuel line and the line from the tank to the fuel pump.
It will still vapor lock after a 20 minute drive and a 10 minute heat soak.
Engine temp remains normal.
On a family vacation two weeks ago, we stopped at Mount Airy, North Carolina.
We expected to see Andy and Barney at the Andy Griffith museum but we found a car show instead.
Low and behold, there was a beautiful 55 Desoto. I spoke with the 80 year-old owner at great lengths.
He restored the car 12 years ago, added A/C and converted to 12 volts. It was gorgeous.
When I asked him about vapor lock, he said he cured it on his car by using Sunoco REC 90 that has no ethanol.
Does anyone use REC 90?
A half hour down the road I kicked myself for not taking pictures of the data tag and engine number for Dave. Sorry  |
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Expert 5K+
Posts: 9911
  
Location: Lower Mainland BC | .
Gerard: Alcohol will definitely evaporate easier than straight up gasoline. So try a full tank of the Sunoco REC 90 (after using up or syphoning out what you have in the tank right now) and see if there is a change. My guess is that there will be
an improvement.
Up here in Canuckistan, the Chevrons have 87, 89, 91 and 94 octane gas. While all four have "Techron" (probably a bit of Toluene (??)), only the 94 has zero ethanol. The others have up to 10% ethanol. The 94 is pricier (than our already stupidity expensive gas prices - lots of taxes added on in BC), I try to run it whenever the price drops enough that I don't have to report a rape to the police. (Ouch).
As for not getting the photos of the cowl data tag, VIN and engine number on the 55 Desoto, there are three of us who currently appreciate and "file" this info for future use: frwl (Igor), RDP (Robert) and 56D500boy (me). I tend to focus only on 56 Dodges but Igor and Robert have a much wider interest.
If you were presented with a photo opportunity like that in the future, the other photos (in addition to the cowl data tag, VIN and engine number photos) would be the overall car, showing the paint combo and exterior trim, and the interior (assuming that it was using stock fabrics, etc) including the shifter cluster, i.e. PF or TF.
Good luck. Try a good tank of REC 90.
"REC-90 is an ethanol-free, 90 octane unleaded gasoline blend designed for use in recreational/marine engines which can be damaged by the ethanol found in other gasoline blends. It is also usable in some aviation engines and automotive engines, though it has not been thoroughly tested for cars and trucks."
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Expert
Posts: 3035
 
Location: N.W. Fla. | On my 331 Hemi, using E-0 gas, usually 87 or 80 octane, I found I had to install a phenolic spacer under the carb to keep it from crapping out at stop lights after running a ways. Also uses a HH alloy Squeeze plate. Back in the 90s-mid 2000s the 331 Hemi I had in a '47 Plym only had the squeeze plate & no problems. Guess gas had deteriorated in quality between '05 & '09 when I got the '60 Plym going. |
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Veteran
Posts: 101
Location: Palm Beach County Florida | I did not get to the gas station yet as I still have 3/4 tank, but I got stuck again today. Same pattern as previously, a hot soak and subsequent stall after starting. The fuel pump was running rat-tat-tat-tat not the normal click-----click-----click. I took the gas line off the carburetor - nothing. I took the gas line off the fuel filter inlet on the chassis rail under the driver seat - nothing. I sat and waited 45 minutes and everything working normally. Last week I had wrapped header wrap on the exhaust pipe where it runs near the fuel line and gas tank. I guess that was not necessary. I have called to get a replacement fuel pump under warranty. |
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Veteran
Posts: 148
Location: Mandurah, Western Australia | Does your fuel tank cap have a working vent? |
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Expert 5K+
Posts: 9681
Location: So. Cal | I would go over your fuel line very closely to see if there is a kink in it somewhere - something that is inhibiting your pump from doing it's job. When I experienced a similar problem with my '67 Barracuda, it turned out to be a partially plugged fuel line from the tank. After disconnecting it from the tank & pump, I blew it out with compressed air from both ends, and crap shot out of it. After that, no problems. |
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Veteran
Posts: 101
Location: Palm Beach County Florida | Gas cap vent! I was associating the gas starvation to the heat but it could be vacume. I should have thought about that. I was getting gas odor in my garage last year and I ordered a new cap. Gotta check that today. |
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Expert 5K+
Posts: 9911
Location: Lower Mainland BC | JedRhule - 2023-09-14 6:38 AM
Gas cap vent! I was associating the gas starvation to the heat but it could be vacume. I should have thought about that.
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Elite Veteran
Posts: 655
Location: Finland | The only way to get rid of odors and oil drips is to sell the classic car and buy a an EV...these are pigs on wheels after all and have always been.. |
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Veteran
Posts: 101
Location: Palm Beach County Florida | Gas cap is a G-37 and I checked that it vented properly.
I have eliminated all the other causes so I assume I have a defective fuel pump. It has a one year warranty. |
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Veteran
Posts: 101
Location: Palm Beach County Florida | While waiting for a replacement fuel pump, I drained the gas and put in 5 gallons of ethanol-free gas.
I drove the same route, with heat-soak time, that caused the vapor lock earlier and the car performed perfectly.
Can it be that simple?
Of course, the outside temps here in south Florida have dropped to the mid 80's from the low 90's.??? |
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Expert
Posts: 3035
Location: N.W. Fla. | JedRhule - 2023-09-23 11:36 AM
While waiting for a replacement fuel pump, I drained the gas and put in 5 gallons of ethanol-free gas.
I drove the same route, with heat-soak time, that caused the vapor lock earlier and the car performed perfectly.
Can it be that simple?
Of course, the outside temps here in south Florida have dropped to the mid 80's from the low 90's.??? Possibly. Also gas comes in Summer & Winter blends, Summer is less prone to evaporation in the heat. Never have heard if done also to the E-0 gas. |
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Extreme Veteran
Posts: 341
Location: Wisconsin | JedRhule - 2023-09-23 11:36 AM While waiting for a replacement fuel pump, I drained the gas and put in 5 gallons of ethanol-free gas. I drove the same route, with heat-soak time, that caused the vapor lock earlier and the car performed perfectly. Can it be that simple? Of course, the outside temps here in south Florida have dropped to the mid 80's from the low 90's.??? Yes, ethanol gas becomes volatile at a lower temperature than ethanol-free gas, so that certainly is going to help your situation, possibly even resolve it.
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Expert
Posts: 2596
Location: Upplands Väsby, Sweden | I had problems with vapor lock on a newly rebuilt engine 383 RB. As soon as I stopped, I couldn't start the engine. The fault was this, which had become worn and was not included in the renovation estimate. It turned out that it was worn at one end and then it could not put on the fuel pump lever. Chrysler Big Block Fuel Pump Push Rod
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Board Moderator & Exner Expert 10K+
Posts: 13054
Location: Southern Sweden - Sturkö island | The reason for the wear of the pump push rod is the lack of zink & phosfor in the oil. I always use ZDDP additive to the oil. |
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Expert
Posts: 3400
Location: Chestertown, NY ( near Lake George) | Still have 2 new ones in my tool box, went thru 2 of them as the stock ones wouldn't work with a steel roller cam in my 426 Maxwedge. |
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Extreme Veteran
Posts: 406
Location: Hilltown, PA |
Where is your electric pump mounted?
In general vapor lock of the type you describe is attributed to the "quality" of todays gasoline. This is partly true, and as pointed out is mostly (but not all) due to the addition of ethanol is significant quantities which makes the fuel more likely to vaporize - or at least the methanol component - which plays havoc with older fuel systems.
In order to overcome this issue you need to understand why modern fuel systems don't suffer the same problem. In a modern fuel system, which is going to be fuel injected, the gasoline is sent from the tank to the engine by a high pressure pump mounted inside the fuel tank. This is important because it means that the entire fuel system is under pressure, and it is this pressure that prevents the fuel from flashing to vapor anywhere in the system. Think about your radiator - the whole reason you have a pressure cap is because the pressure on the coolant raises the boiling point - the same physics applies to any liquid including fuels.
In addition, modern fuel systems retain pressure even when the pump is shut off to prevent hot soak fuel vaporization. This is done with check valves in the pump and regulator.
So knowing this, we can also deduce that lowering the pressure over a liquid like gasoline lowers its boiling or flash point - and this is exactly what an old mechanical pump does. When you "suck" on a fuel line you lower the pressure to invite the fuel to flow, unfortunately you also invite it to vaporize.
When installing an electric pump on an older car you need to install that pump as close to the fuel tank as possible, and also as low as possible so that the pump creates a siphon from the tank on its inlet side. Many people don't understand how important this siphon is, but it is this siphoning action that puts at least a little pressure on the inlet side of the pump. By mounting the pump as far back as possible you ensure that the entire fuel line from the pump to the carburetor is under pressure. Mounting the pump even a few feet forward of the tank defeats the entire purpose of installing it. Ideally you would mimic modern fuel systems and install an in-tank pump and a regulator as close to the carburetor as possible.
Another issue is the type of pump you are using. Inexpensive tat-tat-tat or plunger action pumps may or may not have check valves in them to prevent fuel pressure bleed off. If the fuel pressure can bleed off when the pump isn't running, then the fuel can vaporize during a hot soak, and now your cheap pump has to work harder to re-prime the system. By using a good quality vane style pump and matched regulator the system will maintain pressure when shut down, and be able to provide instant pressure to that carb when the pump is turned back on.
The second cause of vapor lock issues on a hot soak is vaporization of the fuel in the carburetor. Many folks combat this by installing an electric fuel pump and running it for a few seconds to refill the carburetor before starting the car. The truth is a properly installed electric pump will refill the carb in a matter of moments, so "priming" shouldn't be necessary.
Gregg
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Expert
Posts: 3035
Location: N.W. Fla. | wizard - 2023-12-04 8:02 AM
The reason for the wear of the pump push rod is the lack of zink & phosfor in the oil. I always use ZDDP additive to the oil. Or use pre-SM oil.... |
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Expert
Posts: 4043
Location: Connecticut | wizard - 2023-12-04 9:02 AM The reason for the wear of the pump push rod is the lack of zink & phosfor in the oil. I always use ZDDP additive to the oil. Using a ZDDP additive is a waste of money. In order to be effective, the zinc must be blended into the oil at the time of refinement. Use a high zinc oil, like Valvoline VR1. Regarding the vapor lock issue, there is no need for an electric fuel pump. These cars ran fine back in the day with a manual fuel pump. Today's fuel doesn't evaporate as fast as you may think. Verify that the fuel line isn't excessively close to the exhaust manifold.
The heat soak issue, where the fuel in the bowl is evaporated in a few minutes, an hour or a day just doesn't happen unless the carb is sitting directly on the intake without a gasket. If you want, add a phenolic gasket between the carb and the intake. Then if you are still experiencing a hot start issue, open the shop manual and go through the diagnostic procedure. Ron |
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Vapor Lock
