Vapor lock - 1965 390

Scott Fonner

Scott Fonner

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Gold Member
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Oct 3, 2016
Thunderbird Year
1965
Engine runs fine, never an overheating issue, but as engine is at temperature it has an irregular engine pace. At stops I use the brake and give it a little gas. Recently shut off and wouldn't restart until cooled down, about 30 minutes. Believe it's vapor lock.
Opinions on type of gasoline radiator and braided fuel lines requested. Thanks in advance.
 

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Has the engine or fuel system been modified from stock? Do you have a carb spacer inbetween the carb and the intake manifold, and if so is it heated with engine coolant like mine is? Also, what are the ambient air temp conditions when this happens?
 
Original 4 barrel, stock. Uncertain of spacer. It was a very hot day, 90+, but also has the irregular idle on moderate days when engine is warm.
 
Hey Scott. My '64 has never had vapor lock so I tend to believe that is not the issue.

A carb spacer has two functions, 1) it increases engine torque and throttle response, and 2) it can help to insulate the carb from the heat of the engine and reduce the chances of gas boiling in the float bowls. Worth checking to see if you have a spacer. If not, there are spacers made of phenolic resin to provide insulating protection.

A hot engine can run poorly and become hard starting just based on the temperature of air entering the air cleaner. That's why I asked about engine mods. Do you think the engine temperature is in the normal range or could it be running hot due to poor radiator cooling or a stuck thermostat? You can use one of those laser thermometers to see what the actual temperature of the radiator is.

Next time this happens, you can try opening the hood and pulling off the air cleaner, then see if it starts normally with cooler air available.

Doug
 
Check your engine timing. I had This problem when I advanced My timing to far. A good rule of thumb is loosen the distributor bolt and turn the vacuum advance to point to no more than to 7 o’clock if your standing in front of the car. This will give you the best power Perfornance for your engine with a stock carburetor. Make sure there is a spacer of at least 1/4” under the carb. I would Back the timing off to 6 o’clock and see if it starts better when hot. Mine likes about 6:30. There it starts fine in hot weather.
 
64ZCODE said:
Hey Scott. My '64 has never had vapor lock so I tend to believe that is not the issue.

A carb spacer has two functions, 1) it increases engine torque and throttle response, and 2) it can help to insulate the carb from the heat of the engine and reduce the chances of gas boiling in the float bowls. Worth checking to see if you have a spacer. If not, there are spacers made of phenolic resin to provide insulating protection.

A hot engine can run poorly and become hard starting just based on the temperature of air entering the air cleaner. That's why I asked about engine mods. Do you think the engine temperature is in the normal range or could it be running hot due to poor radiator cooling or a stuck thermostat? You can use one of those laser thermometers to see what the actual temperature of the radiator is.

Next time this happens, you can try opening the hood and pulling off the air cleaner, then see if it starts normally with cooler air available.

Doug
Click to expand...
Doug, I did remove the air cleaner and it made no difference. Will look at spacer.
 
I appreciate all the informed suggestions.
 
Hi Scott. Another possibility is the fuel pump is getting dodgy. When the engine is refusing to start, try seeing if the accelerator pump is squirting gas into the throat of the carb or adding a little gas into the carb and see if it will then start. Doug
 
Doug, I did use a spray of ether which didn't help. Will look into other suggestions.
 
Hey Scott

If the ether bunny won't kick the engine over, then it's probably the ignition system. You can check to see if the cylinders are getting spark as follows: pull a spark plug, re-connect it to the spark plug wire, hold the spark plug against the engine block, and crank the engine with the ignition on. You should see a bright blue spark arcing across the spark plug contacts. If not, then spark isn't reaching the cylinder.

If that's the case, could be a failing coil or if you have a stock ignition, could be the condenser in the distributor is failing or the points are degraded. If that's the case, you could replace the points with a Pertronix electronic ignition module and at the same time, replace the rotor and the distributor cap and the coil. That will provide a much better, stronger pulse to the spark plugs. This is an upgrade that will have a lot of benefits and hopefully will also resolve your runability and starting problem.

Doug
 
Am I "way out there", stubbornly believing it's vapor lock? Trust me I'm usually wrong diagnosing this Ol gal. Will check into ignition system, thanks Doug.
 
Hi Scott. Just thinking out loud on this, if an engine won't try to start and the ignition system is functional, then it's a fuel issue. Vapor lock would prevent gas from reaching the carb. However, if squirting ether into the carb won't kick the engine over, then I think you can eliminate the possibility of vapor lock. One possibility is that the engine is flooded. I'm sure you know the procedure for this condition, which is to push the pedal all the way to the floor and crank the engine for a bit to expel the extra gas, then try starting it again.

But, the ignition systems on these old TBirds are weak at best and do a piss poor job of lighting off the fuel mix in the cylinders. The stock coil is pretty weak, coupled with resistor ignition wiring that reduces voltage to the coil in the run condition, and stock spark plug wires that don't convey much spark to the cylinders. Think of pistons the size of soup cans, that's a lot of fuel/air mix to ignite. That's why I advocate getting an electronic ignition module installed, with hotter coil and more conductive spark plug wires. When you do that, you'll notice that the engine is idling faster and you need to back out the engine idle speed screw to get the idle down to where it should be, proof positive of better combustion in the cylinders.

Doug
 
I'll buy that. As always thanks for all the suggestions.
 
Don’t “guess” at setting the timing by turning the distributor to “6 or 7 o-clock”. Who knows if someone my have installed it a tooth or two off in the last 50 years. Use a Timing Light.
 
I would even just get a new preferably a high output coil and see if that helps...somtimes an old coil will start to break down with heat, the more heat the less power it may have
 
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