Vapor Lock and should I buy a new Holley?
 

Hi Guys,

I just got back from a 720 mile road trip to attend the “Corvettes on the Columbia” event in Pasco, Washington. The event was great fun, and my car ran great… except twice.

The first problem happened when we were near Yakima when I pulled off the interstate to refuel. The weather was hot and sunny, with 95 F temps. Leading up to this stop we’d been doing a steady 70-80 miles per hour, with stretches at 90mph+ where the roads were open. All good. The engine ran steady between 180-190F, no signs of overheating, even with the A/C on. When I pulled off the highway the exit led to a stop light. As soon as the car came down to idle speed it simply died.

It would not restart. I tried the usual trick of holding the pedal to the floor, to no avail. A couple of nice fellows in a farm truck kindly stopped and helped push my car across the intersection to free up the left turn bay I was blocking.

After waiting about 15 minutes for the car to cool down, it restarted with some difficulty. I proceeded to the gas station and filled up while keeping the engine running as I was afraid of a repeat of the no-start problem.

We carried on to our hotel in Pasco and parked the Vette. The next morning when it was time to go to the show grounds, the car started up normally.

No issues arose until Sunday when driving home. We stopped for lunch in Yakima and when it came time to start the car after lunch it would not start. Same situation as before: 90+F temps, hot and sunny. This time I put ice packs from my cooler around the hard fuel line to the carb to cool things down. After about 5 minutes I was able to restart the car.

I presume my troubles were related to the dreaded “vapor lock”? My car had no issues with this before. I live in the cooler climate of Vancouver BC where 90 degree temps are rare. Another possible factor is the gasoline I run as here in BC my local Chevron station sells 94 octane premium with zero ethanol. In Washington State the highest octane I could find was 92, which may contain 10% ethanol (or more?) Would the ethanol in the gas combined with very hot ambient temperatures have caused the vapor lock? BTW, the car ran just fine on 92 octane – no pinging or knock at all.

So, was it vapor lock that prevented the car from starting when it was really hot outside? If not, what would cause this behavior?

In other posts I’ve relayed the various problems I’ve had with the Holley 1850 carb fitted to my stock 300hp engine as the original Holley 3810 was removed long ago. I had my current carb rebuilt a couple of years ago. That stopped most of the leaks, and rough running. But this carb still has issues with leaks as I can often smell gas around the engine after shut off. I also think this carb is set too rich as the tailpipe appears rather ‘sooty’. Other issues are the fact that this carb doesn’t have the fuel bowl inlet. To adapt the carb to my car the PO used a piece of rubber hose and screw clamps to attach the hard steel fuel line to the banjo fitting on the carb. Also, other than the small screen in the inlet, there's no fuel filter! Now that itself hasn't caused any specific problems yet, but I'm sure the day will come when a bit of gunk will get inside the carb and cause trouble.

The car’s been like this since I got it five years ago. I'm now thinking it might solve a number of issues if I replace this carb with a correct Holley 3810 carb. That would solve my fuel line and filter issues. It might also address the persistent leaks, gas odor, and rich running, etc.

Brand new Holley 3810 carbs are still available from Specialty Parts Direct for a rather pricey $750, But considering the time and trouble I’ve had with my present Holley I’m sorely tempted to just lay out the cash for improved reliability and safety. If any of you have experience with Specialty Direct and their new Holley 3810's then I'd love to hear about it!

Your thoughts on the vapor lock, and the merits of replacing mycarb with a correct Holley 3810 are welcomed.

You describe vapor lock, it sure could be vapor lock or a related condition exacerbated by high alcohol content or poor fuel line routing. But it could be a tired coil too. Why you believe a different carb, correct or otherwise would fix this I am not sure, but it might!
I was once tortured by a correct Holly on a Chrysler 440, similar symptoms as you describe. I pushed that car and begged it as if a stubborn camel one too many times until I slapped a Edelbrock AFB on it and never looked back.

In your case you should want to know what the problem is. When it won't run you need to establish what's missing - gas or spark.

Dan

I don't believe you were experiencing vapor lock but rather a combination of heat soak and fuel percolation. The heat soak happens when you slow down and shut your engine off at those temps and there is not enough air being sucked throw the radiator. In your case it is compounded by your A/C condenser (which is the system's radiator) that is dumping additional hot air onto your radiator. The stopped engine builds additional heat and it typically will effect your starter more than most other things due to the expansion from the heat and you will experience starter bind or what sounds like a weak battery.

Fuel perc is compounded by the ethanol fuel we have today. It will boil in the float bowls and effect the air to fuel mixture. Most members here have found that if you turn the engine over a few revolutions without touching the accelerator and then hold it 1/3 down while continuing to crank it will start but run rough requiring some "feathering" of the gas until it clears up.

I assume you have a mechanical fuel pump. If that is not correct, please tell us.
Vapor lock describes a fuel pump that is unable to pump fuel because the liquid gasoline inside has vaporized. Cooling the pump is the short term solution. .... If the liquid gas is not vaporized in the fuel pump, but in the line going to the carb or in the carb float bowls themselves, that is called percolation. Percolation can be solved by turning the engine over so the pump pushes liquid gasoline through the line to the carb to cool them and replace the vaporized gasoline. Of course it is possible to have both vapor lock and percolation, in which case the only solution is to cool the fuel pump. .... There are two common long term solutions to these problems. One is to shield the fuel components from heat (e.g., insulated carb spacer). The other is to add an electric fuel pump and fuel return line. As it is farther from the heat of the engine compartment, the electric pump is less likely to vapor lock. And having a fuel return line allows fuel to constantly circulate through much of the fuel system to help cool both the fuel and the components.

None of the these problems are likely to improve by changing carburetors.

Very good information in both responses. I dealt with a "correct" Holley on my '66 until finally replacing it with an Edelbrock AFB, very similar to the Carter AFB that served me faithfully over 40 years on my '65. But, replacement was for reasons other than vapor lock or similar conditions.

I did deal with a similar problem on the '66 some years back that I assumed was either vapor lock or fuel percolation. Leaving the car sit for 30 minutes or so would usually solve the problem on mine as well. After fighting the problem for a few frustrating months, I finally figured out the root of my troubles was a weak fuel pump, just barely getting enough fuel to the carb to run. I really don't remember how I finally determined that the fuel pump was the culprit (too long ago . . . . . ), but once it was replaced there was no more "percolation" or "vapor lock" problem.

Worth taking a look!

What 68hemi said.

Seems there's two definitions of percolation in the car world..
One is the fuel is vaporizing in the pump, line and/or carb.
The other which I use is the fuel is percolating from the float bowl to the intake.

After the engine finally starts, does it seem flooded? (black smoke, running slightly rough)
Is your fuel pump manual or electric?

When you're running down the road the fuel entering is cool from the short time it spends in the line and carb. Now you stop the car with 190* water temp which will rise because the engine heat is absorbed by the water. The fuel in the line (after the pump) and in the float bowl expands as it's heated. The expanded fuel ends up in the intake manifold leading to a flooded condition. Now you'll have to wait for that percolated fuel to evaporate before it's going to fire. I'd start with checking the carb float level or just lower it a tad and see what that does. Holleys are easy with the carb on the car.

A Holley float level test but it's possible to spill fuel on the hot engine.
After the engine is running hot turn it off and wait 15 minutes, then pull the float level sight plugs in the float bowls. (I put a rag under the sight plug to catch any spilled fuel) If fuel comes out, lower the float. Repeat as necessary.

You can also just pull the air cleaner and watch with a flashlight in the carb throat to see if it's dripping fuel after hot engine is turned off.

I've had the same situation you're describing before which Holleys seem to be more prone to it. Fixed by making the fuel and/or engine cooler. There's many methods. Cooler thermostat, block the heat crossover passage on the intake, make sure heat riser valve on the exhaust manifold operating, carb insulator, lifter valley splash shield if you don't have one, and/or float level drop.

Also wouldn't hurt to test the temp gauge by using an infrared temp gun on the thermostat housing. It could be running hotter than you think. Corvette electric gauges aren't well known for their accuracy mostly due to ground problems but sending units can vary greatly. I lived year round near Palm Springs many years and dealt with making vintage cars run in hot temps a lot.

I've posted a ton of info on here about this problem - including spacers/fuel injection gaskets/etc for percolation and adding a "booster" electric pump for vapor lock (and yes they are different symptoms of the same problem - heat)...

A search will turn them up in spades.

You have received plenty of great advice and info from everyone. I'm just adding, most folks do not take into consideration that when we turn off our engines the hottest water rises to the top of the cooling system. Therefore, your gauge may read an accurate number in Degrees while running, (water circulating), but the poor Intake Manifold and Carb. get the hottest water around at shut down. Al W.:flag:

Those with real temp gauges that work know this when the needle pegs after a quick heat soaked hot restart. No question about it, our old carbureted cars often struggle to cope with gas laced with alcohol in hot weather. As Frank indicates, there is a lot of info on this forum to help you deal with it.

Dan

Alex, a couple of things you didn't mention is if you happen to have headers on the car, or what ignition system you're using.

The 1850 Holley has been around a very long time and works well when everything is in order. I have experienced an issue in the past with the pressed in plug on the secondary bowl weeping. This could account for a fuel smell at times. Some J-B Weld does a good job of sealing them, but otherwise the carbs are very reliable. I do recommend replacing the rubber fuel hose with a solid metal line as soon as you can. Lars Grimsrud has a paper available that has excellent instructions on how to make you own line and it doesn't cost much at all. PM him and I'm sure he can send it to you. :thumbs:

This is a 2818 from a 1965 L-79, but similar to what you're describing...
https://cimg1.ibsrv.net/gimg/www.cor...ec492f31ec.jpg

I've also used an aftermarket carb heat shield between the manifold and the carb. They are inexpensive to make and do an excellent job of keeping manifold heat away from the float bowls. They are also quite easy to make yourself out of a thin sheet of aluminum. Just make a cardboard template that clears any carb/manifold obstructions and transfer to the aluminum. Cut, trim and fit to your application. Add one additional gasket and it shouldn't create hood interference. You can also order one from JEGs or Summit. I prefer to make my own, but you can also trim an aftermarket to fit your particular application as well.
https://cimg2.ibsrv.net/gimg/www.cor...26c815577c.jpg
DEI also offers a wide variety of heat shielding that can be slipped over any fuel lines that may be getting too much heat from the exhaust manifolds or headers. A lot of the aftermarket vendors carry it or you can order it directly from DEI.
https://cimg9.ibsrv.net/gimg/www.cor...79911d1f63.jpg

Finally, if you are running a points distributor, one other thing to check (after a long extended run at high speed and high heat conditions) is the point gap. I've had the gap close up under these conditions when traveling from Flagstaff Arizona (cooler high altitude conditions), to Gila Bend Arizona (hot low altitude conditions), where the car wouldn't start after stopping to refuel, only to find the point gap almost nonexistent. The old 'match-book cover' trick solved the problem very quickly. :D

Good luck... GUSTO

It would not hurt to insulate your hard line from the fuel pump the the Holley carb with high heat tubing........I got mine in black............. Lots info and great comments........

Had same issue with my 66 put a phenolic carb spacer under carb problem solved:thumbs:

That is the first time I have heard this theory of the float height causing the issue. It makes a lot of sense. I always battle heat soak on my Holley 2818. The car always fires up instantly when it's not heat soaked, but on a hot day, forget it. I will have to lower my fuel level a bit and see what effect it has.

if your intake has the "heat slot" under the carb plug both end to keep the exhaust heat from the carb .. remove the spring from the heat riser valve so it stays open .https://www.google.com/search?q=inta...CaE-T0wKItIZM:

I 100% agree with this post. This has been my experience with personal, customer, and fleet cars with carburetors ever since the fuel was reformulated for fuel injection and alcohol was added. I eliminated it in my '67 GTO by re-connecting the vapor return system, and helped it a bit in my '61 Corvette by installing Masonite carb insulators. Living where it is HOT 4 months of the year, it is a true heat soak and percolation is reality.

Hi Guys,

Thanks for your great tips and advice regarding ways to prevent vapor lock/percolation.

I've ordered a brand new Holley 3810 carb to replace the 1850c presently on my car. Although I've had a carb kit put in the 1850c, it continues to have symptoms such as leaks, fuel smell, erratic hard starting, etc. The fuel line is cobbled together with the last section to the carb being a bubba'd piece of rubber hose instead of the OEM steel fuel line direct to the carburetor. That carb dates back to the early 1980's and I'm done with battling it and fearing an engine fire.:ack:

I'll also be going thru the entire igintion system to establish a baseline: new coil, wires, plugs, points, rotor and cap. The stuff on the car now is of indeterminate age and I've had the car for over 4 years.

I'll post an update once the new carb is installed.

Shit I shoot

Almost 5 year old post.
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