Vapor lock?
Yesterday, for the second time this summer, my 60' 2x4 experienced what if believe to be vapor lock. Both times the temp was 90+ and the car starts and runs fine however, after about a 1hr. drive it will drain the battery trying to restart. The 1st time this happened I had my wife push the car, can't drive a stick, and we got it restarted-only to again die when I stopped to let her back in. After repeating the process a second time she jumped in as I drove by and as long as I kept the rpm's up it continued to run. Yesterday, not having my wife along, I removed the air cleaner before the battery ran all the way down and the engine restarted but still required high revs to continue running. If this is vapor lock are there any remedys besides the ones I have tried?
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Re: Vapor lock?
It could either be vapor lock or flooding.
Vapor lock occurs when the fuel in the feed line to the pump gets hot enough to produce excess vapor, which the fuel pump cannot handle because it is designed to pump liquid, not vapor. Vapor lock can cause the engine to stall while running, or it can occur on a restart due to loss of fuel in the bowl due to hot soak percolation and vapor in the feed line to the pump, so the pump cannot refill the bowl. The result is too lean a mixture to light the fire.
Many vintage Corvette owners have problems with hot restarts in hot weather. This may be flooding due to percolation of fuel from the bowl that causes and overrich mixture that will not light.
In this case the best thing to do is open the throttle at least 3/4 and crank the engine until is starts. The high throttle opening will prevent fuel flow through the idle/off idle and main systems due to low manifold vacuum and venturi signal. Cranking with high throttle opening just pumps air through the engine, clearing out the excess fuel vapor, and when it gets below the rich ignitibility limit, the engine will fire.
The basic procedure should be in your owner's manual and is referred to as starting a flooded engine or "unloading".
So next time this happens, try the unloading procedure. Crank the engine with the throttle at least 3/4 open. Try five to eight seconds of cranking. If it doesn't fire, stop cranking, but keep the throttle open. Wait a few seconds and crank again.
If the above gets the engine to fire the problem is probably flooding due to hot soak fuel percolation. If it still won't fire, it could be vapor lock in the fuel feed line to the pump.
You can also do the smell test. Stick your nose close to the exhaust pipe. If you detect a stong fuel odor, it's flooded. If not, the problem is probably vapor lock.
If the engine will be shut down for less than an hour, it's a good idea to open the hood. Free convection will cool things down. If you don't want to open it all the way, just pop the hood release for that first inch of opening, which will also allow free convection to vent the hot underhood air - just not as fast.
Another test is to remove the air cleaner(s) at idle, then shut down the engine. Look at the main venturi discharge nozzles and make sure liquid fuel does not drip out of them. If it does, the bowl fuel level is too high or the needle and seat are leaking.
And if you haven't already done so, check that the heat riser moves and wire it full open.
DukeLast edited by Duke W.; May 28, 2012, 09:38 PM. -
Re: Vapor lock?
I had what sounds like the same problem as you with my 1x4. I had to purchase a phenolic spacer to go between the carb base plate and the top of the intake manifold. The spacer is a poor conductor and it reduced the temp enough that it never happened again. There is probably several discussions of the spacers in the Archives.Comment
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Re: Vapor lock?
Duke,
Thank you for the insight and describing both Vapor lock and Hot soak fuel percolation. As a result I now know that the problem is hot soak fuel percolation and not vapor lock. Prior to posting my request I did search the Archives however, no one ever answered the question the way you have. Again, thank you.Comment
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Re: Vapor lock?
Richard, I am getting numerous phone calls a week from fuel injection owners having the same problem as you have. They don't like it when I mention it is only going to get worse as the % of ethanol is increased. So I am very patient and give them numerous things to try that may improve the situation a tad.
One solution Richard is better fuel. If you can do something about the heat under the hood that will help too.
Removing the hood would be a big help (quote from a former national judging chairman aka Dennis Clark).
He was clowning around but was actually telling the truth.
One could write a book on this subject but what it boils down to is the gas is boiling and killing our cars.Comment
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Re: Vapor lock?
Using non ethanol gas will help with this problem. That product is becoming more available. A local Valero station has a dedicated non ethanol pump (90 octane and not too expensive.) That phenolic plate will also help much. I have a '71 Olds 442 that had this problem. The above fixed it.Comment
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Re: Vapor lock?
winter hood, summer hood......Comment
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Re: Vapor lock?
My understanding is that the original design for the 58' vette included a functional vented hood to remove excess heat however, Zora vetoed the idea and we were left with the one year only non functional wash board hood. Was Zora wrong?Comment
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Re: Vapor lock?
Zora did not have to contend with "Obama Gas"Bill Clupper #618Comment
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Re: Vapor lock?
You should be able to find non ethanol gas in your area at pure-gas.org. I was able to find stations all across Washington state last year on a road trip.
PhilComment
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Re: Vapor lock?
"My understanding is that the original design for the 58' vette included a functional vented hood to remove excess heat however, Zora vetoed the idea and we were left with the one year only non functional wash board hood. Was Zora wrong?"The problem in C2s is a vented hood will drive the hot air directly into the HVAC inlet at the base of the windshield. That's why the hood vents are fake.
I believe C1s pick up heater air up front, but the fresh air vent is at the base of the windshield.
About fifteen years ago the Cosworth Vega guys got all excited about a vented hood. A few of them bought them and the cars were virtually undriveable in the summer. All that hot underhood air went right into the HVAC system, and these cars were already hot to begin with in summer weather.
I told them they were nuts, but a few went ahead and spent several hundred dollars on the seeping piles. I doubt if any are still installed.
DukeComment
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Re: Vapor lock?
I'd like to know what gas all of the people are using that have this problem. I don't on my '65, even in 90 degree plus weather. I use Shell Vmax. I do need to feather the throttle for a few seconds and drive off as soon as possible, but I don't understand why everyone is having such problems. My guess is that people are buying their gas at Walmart, or Costco (and it's made in china). That, or they're trying to get their car to idle at 600 rpms. Or, they're using dated wires and the doghouse for the distributor. I couldn't get mine to idle very well with those, either.
People have been blaming ignition problems on the fi units (and now Obama) for 50 years.
GeorgeComment
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Re: Vapor lock?
My 63 with a JB rebuild seems to run fine with shell Vpower, 100LL and now I'm trying shell high test. Seems to run and start fine. Use it every week throughout the year in NJ.
My 61 with a 62 FI unit is about ready to rumble and I will try to get a 2nd hood for summer driving just to be 'cool'. Not sure how to mod it or if it will be needed but it would make a neat project and experiment.Comment
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Re: Vapor lock?
Regardless of what "brand" of gasoline you use, what you get is likely from the same refineries and distributors.
EPA regs tightly control gasoline properties like the distillation curve and Reid vapor pressure, which are primary considerations for vapor lock and percolation. There are also limitations on certain hydrocarbon families and some specific compounds.
About the only differences in brands are the additives including detergents. The majors have their own formulations and advertise them heavily in an attempt to differentiate their product. EPA regs require detergent additives, and there is an ASTM test that all have to meet.
Gasoline, nowadays, is basically like engine oil - generic - but instead of two generic formulations for motor oil, gasoline has one for each area of the country, and there are something like a dozen or more different areas, and for each area the properties vary by season.
There was a lot more quality variation back in the sixties when there were only a few industry standards for gasoline.
DukeComment
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Re: Vapor lock?
Now that's funny Clupper.
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