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5thhorsemann

Vapor lock questions for the hotter climate guys

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The eastern seaboard is getting roasted lately, yesterday we hit 103 and I had parked the car in the sun after a spirited highway run. Like 15 min. later I got in started fine and off I went, I didn't make it a half a block when she started to go heavy lean so I ducked into a parking lot where it sputtered and died and I drifted into a shady spot and popped the hood.

I got a gallon of water and cooled the carbs (twin su r/t's) fuel pump and hard lines. After a little coaxing I got her to start again and got myself to an air conditioned bar.

Today its over 100 again, I did a short run to the gas station and the hardware store and back home. I parked in the sun for only 4 or 5 minutes, started it up and a half a block down the road it sputtered and stalled. I did the water trick and off I went. It seems to be that only when she's parked in the sun will she get hot enough to stall. It seems like opening the hood and splashing water on the fuel delivery components is enough to fix the vaporlock, so I'm not that concerned about it.

My question to the desert dwellers is, how did you modify your cars to combat the vapor lock issues on your early carburated 240 Z? I did a search and read a bunch of stuff, but vapor lock is a hard search.

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Typically, the daily temps reach over 100º every day from June to early October here in the SoCal desert. They're usually 110-115º this time of year. Even with the A/C on, I haven't experienced vapor lock with my '71 Z. The only mods on the car are a bigger radiator and aux electric fans that come on with the A/C.

Prior to getting my current Porsche 914-6 which has carbs, I had a 914-4 with fuel injection that was easily vapor locked. A wet towel on the fuel lines helped with that car. Slow stop & go traffic on hot pavement was deadly - had to keep the air moving through the engine compartment.

Dennis

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These cars are know to have vapor lock problems. They came with asbestos insulation on the fuel rails. If yours is deterorated or missing the problem will be agrevated. One of the Datsun solutions starting in '72 or '73 was adding an electric fuel pump near the fuel tank to push the fuel against the vapor pressure. Perhaps you could add an electric fuel pump.

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I've heard of carb guys recirculating their fuel. Maybe you could put a fuel pressure regulator right at your carbs, with a return flow line that feeds to your fuel/air separator (draining back into the tank). I don't know whether any of the lower pressure regulators are built that way (i.e. like the higher pressure EFI regulators).

FAIW, my 280 will get a momentary vapor lock now after only a few min of sitting. This heat is brutal! I feel for you!

Edited by FastWoman

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The 240Z has a fuel return line. Make sure that it isn't plugged.

With an electric fan, and an electric fuel pump I haven't had any problem with vapor lock, even at ZCON last July (When the temp was around 100). But my Z doesn't have air conditioning, so I don't drive it much when the temperature gets above 90F.

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We are running temps of 105 to 114 these days.My 810 runs fine EXCEPT when i park it for 15 to 20 minutes.Then i have a start issue as the fuel has become so hot it has pushed past the reg.FI cars don't vapor lock.

Sarah,since you like tinkering,if you ran a momentary "on" switch to the fuel pump(or FP relay),you could over come this by turning the FP on with the switch.Datsun designed their FI cars to allow power to the fuel pump ONLY when the motor cranking or turning.

Carb guys like the OP-insulate every line you can get your hands on under the hood.A functioning return system is mandatory.

Another possiblility is the injector blower from the later 280 cars.

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I already do that, ZTrain. I've got a switch wired in the console. I prime before every start. I have no trouble starting, but the engine runs a bit rough until I'm first able to take off down the street. Then everything is fine. Perhaps if I primed for longer... But as long as it starts, I'm fine.

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Try priming for 30 seconds.If you can hear the FP,you SHOULD notice a change in pitch.

On a related note,tomorrow i have some running around to do.I'm going to bring my IR thermometer with me just for shits & giggles.

Edited by Z train

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I recently went through the entire fuel circut and cleaned and blew everything out, including the returne lines. I Insulated the the lines using fiberglass matt insulation and reflective foil tape. It seemed to help a little bit, but Sunday the vapor lock happened again after sitting in the sun for 15 min. or so. I guess I will have to put the electric pusher pump back on the car.

When I went with the round top carbs, I was told by many that it wasnt necessary to prevent the VL problem, so it was omitted, one less thing to fail. I guess that was wrong.

I know there is a company called Pegasus racing that has the replacement fuel pump that was installed on the 73 recall, anyone use this pump? http://www.pegasusautoracing.com/productdetails.asp?RecID=85 This is the exact pump that was removed from my car, it has been internally modified since the original install to use less power and pump more efficently, but it is the faucet replacement.

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If you are in the market for an electric pump you might look at the low pressure rx7 pump. I've got them on both of my 240's here in Texas and never had VL. They are very quiet and about $30 on eBay.

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Here we go again. FI cars can, and do vapor lock. It's the fuel that vaporizes. Fuel does not care if the car is carb or EFI, if fuel gets hot enough to exceed vapor pressure...it vaporizes. In a hose, a bucket, a tank, a fuel rail, or ANYWHERE.

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The electric fan on the radiator with an adjustable cool down setting makes about as much sense as anything. Cars sitting heat sinking from the engine compartment plus what the sun's adding would benefit greatly, I'd think from a cooling fan on the radiator trying to get the cooling system cooled down to say 180 for 15 minutes blowing air thru the engine compartment whole you are in the hardware store. Your cooling system will think you are pampering it while in reality you are cooling down everything else..... too.

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Bruce,here it's actually the heating radiating upwards off the asphalt that magnifies the heat.If i pop the hood and leave it sit on the safety catch,i have no issues restarting.

THe wifes 620 is my only carbed vehicle.I have a functioning return system and NO insulation and i have zero vapor lock issues.

Edited by Z train

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Here we go again. FI cars can, and do vapor lock. It's the fuel that vaporizes. Fuel does not care if the car is carb or EFI, if fuel gets hot enough to exceed vapor pressure...it vaporizes. In a hose, a bucket, a tank, a fuel rail, or ANYWHERE.

Fuel injection runs at higher fuel pressure. Fuel and physics DO care about that. That increases the boiling point of the fuel. Also most FI have the pump either in or by the fuel tank. The pump itself never has to try to pump hot vaporized fuel. Also with the higher volume pumps that are run with EFI, if the fuel under the hood is vaporized the pump quickly displaces it with cooler liquid fuel. A properly functioning FI system is highly unlikely to vapor lock. If, while the vehicle is turned off, the system is bleeding off fuel pressure due to a faulty pump check valve, regulator, or injector then the system will be much more susceptible to vapor lock.

Steve

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The electric fan on the radiator with an adjustable cool down setting makes about as much sense as anything. Cars sitting heat sinking from the engine compartment plus what the sun's adding would benefit greatly, I'd think from a cooling fan on the radiator trying to get the cooling system cooled down to say 180 for 15 minutes blowing air thru the engine compartment whole you are in the hardware store. Your cooling system will think you are pampering it while in reality you are cooling down everything else..... too.

Bruce, you hit the nail on the head. Heat soak is the major component driving the problem. With the engine shut down the cooling system is no longer carrying away the heat from the engine. That's why cars have catch tanks on the cooling system. Coolant temps rise after shut down because that big hunk of cast iron and AL is HOT. A hot day, hot engine, no air flow, one can get vapor lock. Popping the hood induces air flow as the hottest air rises and escapes and cooler, relatively, air replaces it. Heat radiating from asphalt is not helping but is just one contributing factor.

Steve

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Fuel injection runs at higher fuel pressure. Fuel and physics DO care about that. That increases the boiling point of the fuel. Also most FI have the pump either in or by the fuel tank. The pump itself never has to try to pump hot vaporized fuel. Also with the higher volume pumps that are run with EFI, if the fuel under the hood is vaporized the pump quickly displaces it with cooler liquid fuel. A properly functioning FI system is highly unlikely to vapor lock. If, while the vehicle is turned off, the system is bleeding off fuel pressure due to a faulty pump check valve, regulator, or injector then the system will be much more susceptible to vapor lock.

Steve

S.O.B,we actually agree on something.

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Yes less likely to. But they still can and do. Saying that they DO NOT vapor lock is FALSE, especially in our older systems. Why else would Nissan add the cooling snorkel in the latest evolutions? For the comfort and pleasure of the injection system? LOL

As a matter of fact, the hot fuel that sits INSIDE the bodies of the hot injectors WILL flash vaporize when the injectors are first fired, as the pressure drops to near atmosphere for the split second, each time the pintle fires. Yes, it happens that quickly, and affects how the FI car runs, until it clears up with cooler fuel. Note: Nissan pointed the blower snorkel at the injector bodies, not the rail.

I have datalogged the effect and can offer hard evidence of this.

Vapor lock in the rail of a 240Z is the same as the vapor lock in an injector of a 280Z. Just on a different scale.

Edited by cygnusx1

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Yes less likely to. But they still can and do. Saying that they DO NOT vapor lock is FALSE, especially in our older systems. Why else would Nissan add the cooling snorkel in the latest evolutions? For the comfort and pleasure of the injection system? LOL

As a matter of fact, the hot fuel that sits INSIDE the bodies of the hot injectors WILL flash vaporize when the injectors are first fired, as the pressure drops to near atmosphere for the split second, each time the pintle fires. Yes, it happens that quickly, and affects how the FI car runs, until it clears up with cooler fuel. Note: Nissan pointed the blower snorkel at the injector bodies, not the rail.

I have datalogged the effect and can offer hard evidence of this.

Vapor lock in the rail of a 240Z is the same as the vapor lock in an injector of a 280Z. Just on a different scale.

Really?Then explain why my Z engine(below) has NEVER "vaporlocked(for lack of a accurate word)

ZMOTOR.jpg

But my daily driver 810 has warm start issues due to the fact that the check valve in the fuel pump is basically shot,thus letting pressure bleed off allowing the vapor to form.But the Z's system is perfect,thus no issues.

Edited by Z train

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They don't all do it. It depends on how much heat transfers into the fuel rail and injectors. How do you know it's not happening? If you have a wideband O2, it can correct for it and you would never feel it. Nice engine bay BTW. Can you watch the EGO correction factors in a cold vs hot start? Is the hood vented? Oh yeah and you are the "merchant of cool!" ;)

Edited by cygnusx1

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1)They don't all do it. 2)It depends on how much heat transfers into the fuel rail and injectors. How do you know it's not happening? 3)If you have a wideband O2, it can correct for it and you would never feel it. 4)Nice engine bay BTW. Can you watch the EGO correction factors in a cold vs hot start?5) Is the hood vented? 6)Oh yeah and you are the "merchant of cool!" ;)

1)Right.The ones with MECHANICAL problems are the ones that do.

2)Are you saying that the engine bay of my turbo stroker is COOLER than the factory issued 810?

3)On cranking?

4)Thanks.

5)Neither hood is vented.

6)Yes,Yes- i am.

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Right, because yours does not vapor lock, no cars with FI do? Read the FSM. What is the allowable decay time for the factory fuel pressure after shutdown?

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