hls3073z

Here is the interesting thing. The Z's don't experience vapor locking until the temperature get's over 95. So if the temp never gets higher than that no problem. My feeling is that the problem happens in the fuel bowls on the carburetors and in that small hose going to the jets, however, if the fuel is recirculated back to the tank then the fuel that goes to the carbs is cooler so it improves the margin. The other thing is that the Z432A may have ceramic coated exhaust pipes and a very good shield over the exhaust header. That would be a much better design although more costly for the mass market that the 240z aimed at.

Here is the interesting thing. The Z's don't experience vapor locking until the temperature get's over 95. So if the temp never gets higher than that no problem. My feeling is that the problem happens in the fuel bowls on the carburetors and in that small hose going to the jets, however, if the fuel is recirculated back to the tank then the fuel that goes to the carbs is cooler so it improves the margin. The other thing is that the Z432A may have ceramic coated exhaust pipes and a very good shield over the exhaust header. That would be a much better design although more costly for the mass market that the 240z aimed at.

I'll do some reading but sounds like POR-15 will be useful. For now I just want to get the engine bay reasonable. Then I can really make a big effort on the exterior. My wife is on my case about getting the car moving so I need to focus on getting the motor back in there, even if the paint in the bay is not perfect. However, I do want to do everything possible to keep away any rust reaperance. The Sherwin Williams guy did not want to talk to me. Only shops. The guys selling PPG were very helpful but I didn't know all the questions to ask, but I'm getting there.

Thanks to both of you. Actually I was thinking about rerouting my fuel lines since I have stubbed off my mechanical fuel pump. That's another topic I need to bring up elsewhere. It looks like the magic word is "catalyzed Paint" and it not being compatible with other stuff. Not knowing what was used 20 years ago on the body would that mean I should totally strip it to bare metal, not pain over it? I could do the hood first to see what happens. How long does it take for bad things to happen if you paint over something that is not compatible? Is it immediate or a long term bleeding thru?

Thanks for your feedback. I have got almost everything out of the engine bay. I removed the brake boost, clutch master and loosened the fuel and brake lines Main thing left is the wiring harness but it is all disconnected at its end points so I could wrap it up. The battery tray and under the brake area are nasty and there's some spots under the brake area too. I was thinking I'd sand blast those rusty areas. I've used phosphoric acid with good results before so I'm thinking about that. I wonder if POR15 is based on phosphoric acid? Would you use POR15 without sanding off the nasty areas. seems like a lot to expect. My main question right now is after I get to bare metal should I spray some kind of primer, rustoleum? Before putting down the real stuff, or does the good stuff Sherwin, PPG or whoever have their own primer that they want used? That's the key question for now. You are a pro and your customers expect perfection, I'm wanting to DIY so I am willing to compromise but I don't want to totally screw things up. At the moment when I see raw metal I just want to seal it off with something before I get going with the good stuff. The outside was repainted 20+ yrs ago but the engine bay is the original 918.

the reason its loud is that I replaced the fan clutch with a totally different flex fan assembly. As it speeds up it flattens out but at low rpm it pushes lots of air which helps the vapor lock situation. Its not terrible but it makes it unpleasant to hit 6k. As I go forward with schemes to reduce the vapor locking I'm hoping to use an electric fan.

Hi Kats, thanks for your response. I understand that you are desiring to maintain stock as much as possible for aesthetic value. Sometimes I don't pay enough attention to that. I should mention that I really enjoyed looking at those photos, your cars are simply beautiful and they have inspired me to do better on mine. Anyway, to answer your question yes, when I bought the car in '76 it was mostly ok, it had already had the 73 carbs replaced by 71's. On hot days it had the problems you described. I was only 26 then, a fresh electrical engineer and didn't do much mechanic work before so I didn't know what it was. Apparently, over time all the other car manufacturers checked for this condition and made redesign if needed long ago I know it happened a long time ago on some cars but I never experienced it on other cars before. The Z would buck and pitch like a horse that didn't want to go. So one time I popped open the hood and I could hear something bubbling. I put my hand on many hot things and then I discovered I could feel the fuel bubbling in the fuel pump. I began talking to people and I discovered that an electric fuel pump was added in the back but I also discovered that it never came on. So it must have never been checked. I decided to make the electric pump run all the time. I added a switch to the oil pressure gauge so that if I lost oil pressure the fuel pump would shut off. I did this in case I had a wreck and the key stayed on so that it would not continue pumping fuel. I did more testing and discovered that the electric pump was plenty strong so I just bypassed the mechanical and eventually totally removed it. That helped a lot but still there were problems on Texas hot days with AC on. So next I installed a flex fan and that improved it a lot. Still some problems happened. I feel that there is a fundamental flaw in the design with those SU type carbs hanging over the exhaust manifold. At the moment my engine is totally removed so I am going to try some shadetree mechanic solutions like sheet metal shields containing foam insulation like a sandwich and insulation around the carb bowls and that small fuel line at the bottom that goes to the jets. Finally, I have a rust bucket 81ZX and I could take those fans and mount them to blow air from the other side of the engine like what was done on the FI on the 81ZX. After that I'm going to try electric fans on the radiator/ac condenser. That flex fan steels HP and is very LOUD. I did not mention it but of course I have rebuilt the carbs and adjusted the float settings but that made no difference, they were ok. 40 years later I now have more time to tinker with it. My daily driver is a duramax diesel pickup that sadly is much faster than the Z.

Hi Kats, I noticed that you still have a mechanical fuel pump and stock fan. Maybe it never gets very hot where you are so you must not have trouble with vapor locking problems. Here in central Texas I must use a flex fan (very LOUD) and electric fuel pump only and I still get a jumpy ride after sitting at traffic light for a while. don

I was surfing around at some 240 and fairlady restores in Japan and I saw a list of documents at the end. http://www.geocities.jp/datsunz903/ Report of study for exhaust humes entering from tail gate Sep 1971 I assume this document was originally in Japanese, is there a translated one somewhere?

I've decided to do a diy paint job on my 73 240 that I've had since 76. It has been repainted once like 20 years ago. For the moment I'm focussed on the engine bay. The motor is out and there's some rust spots that need attention. Then repaint the engine bay to 918 color, put the engine back in and then work on the exterior. After a few phone calls I got the best response from PPG. They had 918 in their system. Sherwin williams wouldn't talk to me and said they didn't go that far back. I'd like to start off small by stopping the rust right away. Pointers to diy docs would be appreciated.

thanks Charles, I wondered about that. I was quite surprised when I talked to the ppg guys that they said rustoleum "no problem". They seemed too laid back. At least they talked to me. When I called Sherwin Williams they said sorry don't talk to consumers and besides that car is too old for our system. I need to go post a question in the body paint section of the forum. I'm just anxious to stop that rust.

No problem there. The whole reason the engine came out was that I was replacing the clutch, (the problem was actually fatigued springs in the pressure plate). The exhaust had to come out and 2 studs twisted off on the header so we decided to pull the engine to get those studs replaced. So, yes, now is the time to do everything I ever thought about. Everything is mostly original, it has about 200K miles on that clutch. For the moment the focus is on stopping rust that has started in the engine bay. Any recommendations on paint for that? Sand to bare metal then rustoleum for primer and then PPG one step for the engine bay is the plan. The PPG guys looked up 918 and sure enough, Mexican Orange, they can do it.

thanks for the feedback. Sounds like its best for me to remove the tranny and 3rd member from the ZX. Then do some measurements. I'll check back with you on mustache later if need be. I would guess that the drive shaft is longer on the 2+2 ZX. Are you confident that the trannys 4 sp vs 5sp zx are the same length? so it should fit the same maybe increase the opening size inside the 240 for 5th gear slot? There was a table somewhere that showed the rear axle ratios so I can figure out the overall ratios. I'd like to get more rpms in the low gears for more torque on leaving the line. edit, I found the table and it looks like 1st gear is 3.0 vs 3.5 for zx vs 240 respectively so the 5 sp would make my off the line jump worse so probably should stick with the 4sp until I can get the rear axle sorted out. My off the line jump experience has been spoiled by my duramax 6.3L diesel in my truck.

I was under the impression that the diffy had to be done at the same time otherwise the dimensions wouldn't work, so I like your suggestion. I assume that the dog bone and mustache bar from the ZX won't work. True there's always work, for a while I thought about pulling the whole ZX drivetrain out and putting it into the Z, get fuel injection all that good stuff. But that's definitely another day.

Bart, I see that you are in the Netherlands. There is a good chance that the design of the car in Europe was different enough to avoid this problem. Are you sure that it ever gets to 100 deg in the Netherlands? ? It is that way almost every day here. Nissan definitely knew that there was a problem that was the reason that they added the electric fuel pump and published that document. Its also probably the reason that they decided to design in that separate cooling fan for the fuel injected Zs. They didn't want the problem to happen again.

Well at least you didn't use your mouth to try to suck fuel into the hose. That has been done by men older than 16. It got dramatically better when I bypassed the mechanical fuel pump. Actually, that and the flex fan made it acceptable but not perfect. I can see the fuel in the fuel filter and it doesn't feel warm so I think the fuel is cool enough. Right now I"m going to focus on that tiny fuel hose that connects between the bowl and jet at the bottom of the SU carb. Thats a small amount of fuel in that hose sitting right over that hot exhaust manifold. It must be boiling in there. There is some clear motorcyle fuel line that might work instead and it may be possible to wrap insulation over that. Only problem is that it has to be flexible for the choke to work. My goal is to eliminate the need of that flex fan. It is very LOUD. Not only that but at low rpm it steals just enough HP that it is noticeable on takeoff.

OK, tks for feedback. Zhed you are basically suggesting put studs up there at the top of the engine. In the process of getting the tranny out the studs on the exhaust broke off. After that happened I decided I really need to paint the engine area due to rust starting so I pulled the engine anyway. Of course I had told my wife that I'd have this thing moving out of the driveway in a couple of weeks. Now I'm thinking about repainting the whole thing. One other headache I have is that my driveway is slightly sloping so that made a problem with jacks etc. So now the decision will be whether or not to mount the tranny on the engine outside the body and then drop it in. One other complication is that I'm thinking about going back with a 81 2+2 ZX 5 speed and diff. I've read elsewhere that it should fit. This is how projects sometimes never end.

On my 73 240 I recently removed the tranny in order to replace the clutch. I got it out, it wasn't easy just using floor jacks and jack stands but I got it out. I was reading the manual and I see that it says to remove engine as well. Is that necessary? Would it be difficult to put the tranny in w/o having removed the engine? I can see that it will be difficult to get the tranny back up in there with engine in place due to the small up high tunnel.

There must be something fundamentally different about your fuel/carb setup. If you read the doc listed at the end they suggest that in the rare situation where the customer drives in 100deg weather you may need an aux fan and then they go on about how to set that up. Perhaps the return line fuel flow limiter was changed. In any case I think the basic problem is that heat exposed to that small hose that connects from the bottom of the bowl over to the carb jet is one source of the problem. See photo attached. I've also attached what I have done to the rear carb and my first pass heat shield. I did all this with the engine in the car so I was somewhat limited.

I was thinking of doing the same thing except instead of that metalic foil sandwich in between I was planning to spray that expanding foam insulation in there. It would require some screw spacers before spraying in the foam but then afterwards the screws could be removed. At the moment I have a glob of that foam around one of the carb bowls. BTW, this problem existed even when I used good old leaded fuel, so ethanol is not the problem. I do hate ethanol, don't get me started.

Yes, it does have a return line. You are correct that it should remove the opportunity for the fuel to get heat soaked in the lines, but if you stop and park the fuel stops circulating so that fuel gets soaked too. I even had the problem with idling at a long red light on hot summer day. I did see something in that doc about changing the fuel flow circulation in the fuel lines. Once you get rid of the mech fuel pump there is no reason to keep those lines going up front but I just never decided to cut them off and reroute near the firewall. Too much plumbing like work. I did run some pipe wrap anti freeze insulation over most of the lines. I think that most of the problem is in those carb bowls that hang right over the exhaust manifold. I suspect that the fuel is boiling in there or in those hoses that go to the jets of the SU's. Since the engine is now sitting out in the open I can get creative with some shielding.

got the doc. great. tks. I wish I had this doc 40 years ago, not kidding. Most of my Z had all the epa plumbing removed when it had the carbs replaced by the 71 versions before I bought the car. One big suggestion is the performance hood. I'd hate to cut up my hood but if I could get another I would try that. I'm trying to remember, did the 280Z FI versions have vents on top the hoods, the ZXs did? The 81ZX I drove to death never had a vapor locking problem, even when using the AC. It was a great boulevard cruiser, cold ac, soft ride, etc.

I'll look into the fuel rail connect points. I have it reversed since it doesn't have to go up front to a fuel pump. The other thing I'm considering is to make that exhaust manifold shield more effective by making another sheet just like it, layering them together and spraying foam insulation in between making sandwich kind of construction. I have sprayed that insulation around one of the fuel bowls. With engine out it will be a lot easier to put some things in place. I wonder how they handled this with turbo installations? That had to get super hot on that side.

I've had this car since '76, it was a daily driver a long time etc. then sat around so now I'm into a restore. From day 1 in 1976 its had vapor locking issues, I live in the Austin area and 100deg days are quite common. The symptom is you drive somewhere on a hot day, leave it parked for 15 minutes, come back and try to take off. It jumps and bucks a but after 5 minutes of driving things smooth out. Stop at traffic light for a while and it might start bucking again at takeoff. I do have an AC, gotta have that. I have done a lot to help this problem. removed mech fuel pump (you could hear fuel bubbling in there) electric pump was there but not wired up properly, so I fixed that. rerouted the fuel lines check carbs for proper float level put an extra shield under carbs above exhaust manifold replaced standard air filter with separate oval round filters. Finally the thing that helped the most is that I switched to a metal flex fan. It pushes A LOT of air at low RPM. Although loud it makes the most difference. So now, I've got the engine out and looking things over to see what else might be done to keep those carbs and fuel cooler. Any advice appreciated. On my list is install one of those ZX injector fans that mount over the spark plugs with ducting over to the carb area. go with electric fan(s) for the radiator. what else?