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Vapour Lock Definition

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I have seen many thread about vapour lock but nothing about what it actually is or how it is caused.

Is it only found on Smog equipt or all 70-78Z's

Can someone who knows about this in detail enlighten us all?

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I'll give it a try...

If the gasoline was all made up of high volatility compounds, then the gasoline would evaporate too easily during hot weather and vapour lock could occur. Vapour lock refers to the situation when the fuel boils in the fuel lines so it cannot be delivered correctly to the engine. When vapour lock occurs, the engine operates as if it was running out of fuel.

The gasoline we buy at the pumps is not the same year around. During the summer, the refiners supply gasoline with a lower volatility to reduce vapour lock problems on our vehicles. This low volatility gasoline also helps protect our environment by reducing hydrocarbon emissions caused by gasoline evaporating. During the winter months, high volatility gasoline is produced to help our cars start better during cold weather. If we try to use gasoline made for warm weather use during a winter cold snap, then the engine may not start! During fall and spring, the gasoline is blended to an intermediate volatility to enhance vehicle driveability during those climatic conditions.

Am I correct?

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Or htis:

Vapor lock occurs when the vapor pressure of the fuel is higher than the surrounding environment. In older engines with "sucking" fuel pumps at the engine the pressure in the fuel line to the tank was reduced by the sucking action of the fuel pump drawing fuel form a fuel tank nearly twenty feet away, and when heated, the gasoline actually boiled creating a vapor of gasoline which the fuel pump could not handle, thus the name "vapor lock".

Today's fuel pumps are in the fuel tank where they push the fuel under pressure to the engine systems. Excessive fuel which is not used is sent back to the fuel tank. This causes a constant flow of pressurized, cool fuel in the lines to the engine system, be it fuel injection or carburetor. As a result you would have to heat the fuel line with a propane torch to get the fuel to boil and even then it would be cooled by the flowing fuel circulating from the tank to the engine and back again to the tank. Vapor lock as we once knew it is a thing of the past.

When gasoline overheats and boils inside the carburetor bowl or fuel pump of a hot engine, it ceases to flow. This can cause stalling or hard starting. This is called vapor lock, and it usually happens during hot weather. If a hot engine won't start, all you can do is let it sit and cool off. You should check the cooling system to see if anything is causing the engine to run unusually hot (a bad thermostat or cooling fan, for example). Switching brands of gasoline may also help.

:eek:

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I think guy must have had an encylopedia for lunch!!ROFL (just kidding guy).He is correct. The carbs on the Z are on top of the exhaust.On hot days when at idle that heat boils the fuel in the carb bowls.Just like boiling water this causes the air in the fuel to expand.Now instead of liquid fuel for your carbs to atomize it has gas vapor.Kinda like when they pump the bottom of the keg at your favorite pub.Beer vapor. Have fun!! Daniel -Oh yeah, the best description I have heard is your car starts bucking like a bronco as the engine gets fuel then vapor then fuel.

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Yep Daniel , I spend my whole lunch time finding the correct answer, so do I deserve an A+?????LOL

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Good job, Guy. BTW, the early Z's didn't come with the tank-mounted electric fuel pump, just the mechanical "sucker" mounted on the engine block.

I wouldn't think vapor-lock would be much of a problem in the UK, but in the southern reaches of the US the 100+ degree days can cause problems. It may help to insulate the fuel rail - I've seen small-diameter tubing insulation on some of the auto parts sites.

My '71 is a "pre-electric", with only the mechanical fuel pump. I wrapped the fuel rail with aluminum foil, shiny side out, ("real" insulation is on my to-do list, albeit near the bottom). Doesn't look very professional, but I don't have vapor lock problems. There is no doubt also a way to insulate the carb bowls, but I haven't tried.

JIM DOZIER

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Hey Jim, The foil insulation has a gotcha.It keeps heat out until it gets in.Then it acts like a blanket in july and holds the heat IN.The shield between the exhaust/intake is the answer. Daniel

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BUMMER, Daniel :( ! You're right, insulation can work both ways. I understand the heat transfer "stuff" (I did stay awake MOST of the time in ChE Thermo class ;) ) and also understand that the "heat entrapment" problem could arise. (Driving a hundred miles and then parking in direct sun for a few hours in August might do it.) However, I haven't had any problems so far.

I agree about the intake heat shield - no Z south of the Mason-Dixon line should be without it:finger: .

JIM DOZIER

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Hey, you think you got problems? Here on the Central Coast of CA we still get 'winter gas' even though the temp never goes below 50 most of the time. It is often 70 or 80 here for good stretches during the 'winter'. This stuff vapourizes at the drop of a hat! Thank God for electric fuel pumps. Just turn the key to 'on' and listen until the bubbles hit the tank (blub-blub-blub-blub) and hit the ignition.

steve77

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Thank you so much guys. Now I know why my car has been broncoing in the heat. I thought it was vapor lock, but you verified my claim. Now I have to insulate my hoses or get a heat shield to cover my exhaust manifold. Any suggestions? The only wierd thing is that my car just started doing this. I had driven it in the heat before with no problem until now. It was 88 degrees F both times when my car got vapor lock. Any more suggestions why it would all of a sudden happen now and not before?

Thanks ahead of time,

Ben

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If it just started suddenly, I doubt it's vapor lock, unless you still have the water line connected to the intake that is.

Sounds like either an ignition problem, bad tank of gas, fuel filter clogged, plug fouled, plug wire shorting across another wire..... if it were vapor lock, it would have been doing it all along, or at least to the point you would have noticed it.:ermm:

Probably end up being one of those things that make you slap your forehead and ask yourself, "Why didn't I think of that"....:cheeky:

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I tend to notice vapour lock during exessive periods of idling, say at traffic lights on a hot day. It occurs when attempting to take off at high speed. It is often quite hot in Australia so its no surprise. I have a heat shield, plus my extractors are HPC Coated to prevent heat transfer...It still happens despite this.

Trick is, to know when it might happen, so you dont end up getting smoked off the line!

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Unfortunately I can't tell you which of the following fixes worked for my vapor locking 73 Z because I did them all at once: Re-installed the mechanical fuel pump(already had the electric running), fabricated a heat shield, hooked the fuel recirculation back up, and insulated all of my fuel hoses with 1/2 inch copper pipe foam insulation from the hardware store. Absolutely no vapor lock anymore. Victor.

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Hmmm... Well I replaced the gas filter and there was a bunch of rust in it. It is wierd because when I first got the car in 99 it sat for awhile and I had the filament and rust removed from the tank. Now it is there again. Also, the diaphragm in the gas pump is sucking in air with the gas. I took it on a drive yesterday and it did not have the problem, but it did feel a little shakey. As regards to gas, I go to this generic place all the time just to support a small business near my home. I am going to start using brand name gas from now on.

I will keep you guys posted on how the car is running.

-Ben

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I just went on a drive and the car drove fine. I didn't go on a long one, but the weather was hot, I went up hills on the freeway, got on the gas some, and drove it around town in traffic. I am hoping that it is the gas filter like 2manyzs said. The car felt like it had a lot of power, but if it was the gas filter, why did it all of a sudden start doing this? The only time that the car would get bogged down was in the heat, on the freeway, and usually uphill. I would think that is when I need the most fuel. I am going on a drive with some guys from the forum tomorrow. that will be the true test. Thanks for everyones comments.

-Ben

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V8 engines sometimes get vapore lock because the carb is too close to the intake manifold and the guel in the carb boils. So they put a non-heat-conducting spacer under the carb to keep it a little cooler.

If you remove the webbing from the intake for the fuel-inject Z, would heat from the exhaust affect the injectors?

thx.

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My 78 280Z exhibits some bucking but only below a half a tank of gas. I has been explained to me that the fuel hose in the tank may have a hole in it and when the fuel gets low it starts sucking air & fuel. I fill the car up & it runs fine. The gas tank has been redone, fuel filter cleaned etc. The only way to fix is to pull the hose and basket by drilling another hole in the tank. The fuel tank seems to be a weak point on these cars especially when the car isn't driven much and allowed to sit. I have been told to keep the tank full when storing.

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On ‎03‎/‎20‎/‎2004 at 6:36 AM, tanny said:

Unfortunately I can't tell you which of the following fixes worked for my vapor locking 73 Z because I did them all at once: Re-installed the mechanical fuel pump(already had the electric running), fabricated a heat shield, hooked the fuel recirculation back up, and insulated all of my fuel hoses with 1/2 inch copper pipe foam insulation from the hardware store. Absolutely no vapor lock anymore. Victor.

Have you got pictures of the heat shields? what material did you use to insulate the metal fuel rail and fuel lines? I have the exact same problem and need a solution to percolation at the fuel bowls!

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@240znz, are you still with us? We haven't forgotten you.

Jalex, As I recall your heat shield is two piece. (can't remember which thread the pic was in.) It's possible that the gap in the shields between the carbs is defeating the intended function. Just a theory.  Instead of all this guesswork on everyone's part (don't get me wrong, treasure hunts are fun) have you, (or any other member with the gremlin), considered using an infrared thermometer to measure the temp of the the fuel system components under the hood? You are still connected to the fuel rail by the valve cover aren't you? I think this was suggested by another member a while back. I'm sure that everyone (including you) would love to have raw data to peruse. I'd start at the firewall and work my way forward to the float bowls. The findings would invaluable to you and others with the same problem.

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Hey all. Be aware that 240ZNZ has been sidetracked by kids, catamarans, mountain biking, craft beers, etc, etc, etc. Plus living in New Zealand itself is a major distraction. Many lame excuses for why his "zed" is still in pieces. Oh, yeah, now it's winter again...just sayin..............

Cheers, Mike

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Anyone heard from the other New Zealander whose avatar was his wife holding a white poodle?  Super nice guy that was a lot of help to the members here. 

Can't think of his name and hadn't seen any comments from him in a year or so. Seems like he had a 2.4 in an Austin Healey?  

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Maybe yer brain conflated Healey Z with New Zealand Z?  See how easy that could be...  (got to use an uncommon word, yay).

 

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