The Dreaded Vapor Lock

[jonathanrussell]

Hi @VaCat33. Sorry about your problem. I have some experience with and thoughts on vapor lock and will share with you. But, in my experience vapor lock doesn't shut the car down for 2 hours. The very worst cases of vapor lock resolve within 30 minutes (in my experience). So, I would at least do some testing on the ignition system. When the car dies, are you getting spark at all plugs? Cap, rotor, points all in good shape? Plugs less than a year old and NGK vs some other brand? As others have mentioned above...is there fuel in the bowls or are they empty for reasons beyond vapor lock? Stuck needle jets? clogged screen where fuel enters the needle jet chamber? Fuel filter? Fuel tank?

Vapor lock:

I spend summers in Hot Atlanta and vapor lock was at one point a problem with my 72. When I have everything set right, I can idle in traffic as long as necessary and it never vapor locks even on 100 degree days.

- I run BP 93 octane gasoline. I need the octane because my E88 head is slightly milled and pinging can be a problem. So, I don't run ethanol free because you can only find it in 89 or 90 around here. I have found ethanol fuel to have a lower boiling point AND....it gets very bad with age. I have found that a tank with fuel much over a month or so old begins to have a lower boiling point...based on my vapor lock observations. I drive my 72 a lot (most days) so keeping fresh fuel in it isn't a problem. When we are out of town for extended periods though I keep the fuel level low so I can fill up with fresh fuel when I return. So, my question is...how old is your fuel?

- During summer I disconnect the air intake hose for Winter and attach a different but same diameter hose and run it through the left side round hole in the radiator support. I then keep the summer/winter switch on the air cleaner in the Winter mode. This keeps cooler air coming into the engine.

- I use a Mishimoto aluminum radiator and stock fan. Temps never reach 50% mark on gauge.

- I wrapped my stock exhaust manifold and carburetor float bowls with a heat shielding product I purchased on Amazon. This lowered my float bowl temps by 20+ degrees.

- I run a Carter P4070 electric fuel pump with no manual pump. I also have a fuel pressure regulator set to about 3.5psi and a fuel pressure gauge in line.

- My fuel tank has been boiled, acid dipped, and coated on the inside, powder coated on outside so....clean fuel.

So, I do believe some if not all of the things above contributed to solving my vapor lock problems. 

As things stand now, the two things that cause my car to run poorly are....

1) any hint of fuel that is not completely fresh.

2) spark plugs older than about 8 months. Even though my plugs look perfect, once they are about 8 months old my car starts sputtering around 5k rpms. Change to new plugs and problem gone.

I have a petronix electronic ignition in a euro spec 240z distributor fyi. 

I hope something I have shared is helpful and that you are able to resolve your problem. Take care and let us know what you end up finding to be the problem.

J

[siteunseen]

23 hours ago, jonathanrussell said:

Hi @VaCat33. Sorry about your problem. I have some experience with and thoughts on vapor lock and will share with you. But, in my experience vapor lock doesn't shut the car down for 2 hours. The very worst cases of vapor lock resolve within 30 minutes (in my experience). So, I would at least do some testing on the ignition system. When the car dies, are you getting spark at all plugs? Cap, rotor, points all in good shape? Plugs less than a year old and NGK vs some other brand? As others have mentioned above...is there fuel in the bowls or are they empty for reasons beyond vapor lock? Stuck needle jets? clogged screen where fuel enters the needle jet chamber? Fuel filter? Fuel tank?

Vapor lock:

I spend summers in Hot Atlanta and vapor lock was at one point a problem with my 72. When I have everything set right, I can idle in traffic as long as necessary and it never vapor locks even on 100 degree days.

- I run BP 93 octane gasoline. I need the octane because my E88 head is slightly milled and pinging can be a problem. So, I don't run ethanol free because you can only find it in 89 or 90 around here. I have found ethanol fuel to have a lower boiling point AND....it gets very bad with age. I have found that a tank with fuel much over a month or so old begins to have a lower boiling point...based on my vapor lock observations. I drive my 72 a lot (most days) so keeping fresh fuel in it isn't a problem. When we are out of town for extended periods though I keep the fuel level low so I can fill up with fresh fuel when I return. So, my question is...how old is your fuel?

- During summer I disconnect the air intake hose for Winter and attach a different but same diameter hose and run it through the left side round hole in the radiator support. I then keep the summer/winter switch on the air cleaner in the Winter mode. This keeps cooler air coming into the engine.

- I use a Mishimoto aluminum radiator and stock fan. Temps never reach 50% mark on gauge.

- I wrapped my stock exhaust manifold and carburetor float bowls with a heat shielding product I purchased on Amazon. This lowered my float bowl temps by 20+ degrees.

- I run a Carter P4070 electric fuel pump with no manual pump. I also have a fuel pressure regulator set to about 3.5psi and a fuel pressure gauge in line.

- My fuel tank has been boiled, acid dipped, and coated on the inside, powder coated on outside so....clean fuel.

So, I do believe some if not all of the things above contributed to solving my vapor lock problems. 

As things stand now, the two things that cause my car to run poorly are....

1) any hint of fuel that is not completely fresh.

2) spark plugs older than about 8 months. Even though my plugs look perfect, once they are about 8 months old my car starts sputtering around 5k rpms. Change to new plugs and problem gone.

I have a petronix electronic ignition in a euro spec 240z distributor fyi. 

I hope something I have shared is helpful and that you are able to resolve your problem. Take care and let us know what you end up finding to be the problem.

J

100% agree with you. I've never experienced vapor lock. 

Your float bowls are low. Don't go by the 23mm, max them out and be sure your overflow hoses are connected to the air box. 

I set mine higher and never have any problems. 

[VaCat33]

Hello

I know it has been a while since my last post, but sometimes other things get in the way of playing with our cars. I did want to close the loop on my post. After many trials and tests we think we have the problem resolved…and IMHO it was not vapor lock, as I originally suspected.

Shortly after my last post, I ran the car on a relatively cool day (mid 60s) and sure enough it died after 40 minutes and would not restart for a while. Given the mild temperature, I began to suspect some other cause, as some of you suggested.

I drove the car to my mechanic’s garage. The drive is about 20 minutes. I got there without problem and left the car running. Within 15 minutes the car died. At that point we disconnected the fuel line at the carb to check the flow. Upon cranking the engine, no fuel was reaching the carb.

We checked and confirmed the fuel line between the pump and carb was clear. So, we installed a new replacement (GMB brand) fuel pump. The car started and ran for 30 minutes or so and died. Again. we disconnected the fuel line at the carb…no gas. At this point we suspected a possible problem between the tank and the pump, so we ran the fuel pump inlet hose directly into a five gallon can of gas. Cranked the engine but no fuel at carb.

I bought a different replacement (US Motor Works brand) fuel pump. Installed it…would not work right out of box. Ran the test with fuel pump inlet hose in can of gas. Cranked engine…no fuel at carb.

We installed a used Kyosan Denki pump…the car ran flawlessly for three hours. So, I acquired a new old stock (NOS) Nikki pump. The engine has been running fine for hours at a time. Totally baffled…could these modern replacement pumps be that bad?

During all these tests where we had the car running for hours, we also discovered a couple intermittent ignition issues…which may, or may not, have contributed to the original problem. Twice while running the car. it suddenly died (no stumbling…just died). A quick check revealed no spart at plugs. The first time this occurred, we had power all the way to distributor. A check of the original cap revealed the center contact was damaged and perhaps causing an intermittent problem. The second time we had no power from the coil. The resistance on the coil tested within specs but since it is a NOS coil, I suspect it might be compromised and failing at operational temperature. All seems to be working fine with new distributor cap and coil.

Thanks for listening and all your help.

Jim

[Patcon]

Good update Jim.

Yes the new pumps can be that bad. I really think it's the valves in the new pumps. Sometimes they just don't seal or they stick open. It shuts off soon after that...

[SteveJ]

Make sure you get the plug wires seated far down enough in the cap. If there is a gap, it will arc between the cap and plug wire, eating away at the plastic in the cap.

As for the fuel pump, a couple of years ago I replaced the fuel pump one someone's car with a Delphi pump. I wasn't happy with the results, so I swapped the diaphragm over from the Delphi to the stock fuel pump. The old pump ran great with the new diaphragm. 

[emccallum]

Jim,  

 Thank you for posting the follow up. It will be a while before I actually crank my rebuilt motor, but I just checked my parts list and I purchased a US Motor works fuel pump! Thanks for the heads up and glad you seem to have it sorted.

ernest

[cgsheen1]

On 8/22/2022 at 5:05 PM, VaCat33 said:

... Totally baffled…could these modern replacement pumps be that bad? ...

My experience is YES, they can be that bad.

I pulled an original off a 240Z that had bad diaphragms and replaced it with one we got from Rock Auto (a GMB maybe?). The new one wouldn't pump fuel. I took it off and could work it manually and it pumped just fine. I started to wonder if there was something wrong with the eccentric in the L24. Then I compared the arm of the new pump to the arm of the original pump and there was enough difference in its aspect that the lobe on the cam wouldn't move it enough to pump. Ordered a different brand and had the same problem. Took a third try before I found a working mechanical fuel pump. 

[emccallum]

This thread has made me rethink my engine restoration. I have old Nikki and Ampco fuel pumps. I believe both are the originals to 240s. After reading a bunch of threads I decided to order a NOS Nikki that according to others has all the same internals as the one for the 240. I will attempt to rebuild one of my old originals and do away with the made in china knock off.