Captain Obvious

My honest opinion is that you're working in the minutia. I don't think there's any meaningful performance benefit to what you did to the valves. Looks pretty? Certainly. Bragging rights? Absolutely! Performance gains? I would have to see the dyno sheet before and after. I'm no engine builder, but I think there are waaaay bigger fish to fry before you start seeing any changes from the surface finish on the valves. Cam changes. Intake tract improvements. Combustion chamber design improvements. Exhaust tract improvements. All that stuff. I think the valves are in the .1% at the very end once everything else has been optimize. The NASCAR and Indy guys who have already squeezed out the other 99.9% elsewhere might see a tiny improvement, but not us. That's my uneducated non-expert read.

So what's the bottom line? It sounds much better. Are you calling this a success now? The thread was about severe driving problems. Are you claiming victory? That would be sweet!

You better. I'm going back into mine this off season.

LOL. MacGyver is still looking over his shoulder after all this. So the tubes on the small engine two-cycle thing... One is supply from the tank to the carb, and the other is the return from the carb back to the tank. The system operates just like the Z. The fuel pump pulls more then necessary from the tank, some of it is used by the carb, and the excess is pushed back into the tank. Continuously circulating. And the closed system operating under a slight vacuum is what allows it to be used in any position without spillage. Like chain saws. And as the fuel is used up, the duck--bill valve on the cap allows air into the tank to replace volume of consumed fuel. I've had that duck-bill check valve plug up on some of my small engine stuff and what happened to me is it runs great for a little while and then will stall and not restart. Too much of a vacuum in the tank and the fuel pump can't pull fuel out anymore. Loosen the cap and it'll run for a little bit and then quit again. So a little vacuum is good, but too much vacuum will starve the engine lean. I don't know why your clogged tank valve resulted in a puddle of fuel. (And it still bugs me. )

The fuel bouncing around would speed evaporation by increasing surface area. In other words, it would reach vapor pressure more quickly as the temperature goes up, or after something like a fuel fill up. When you stop for gas and woosh the cap, you release the vapor pressure. But it will re-attain that pressure when you put the cap back on. About the backpack blower... It's my understanding that the check valve in the cap allows air INTO the tank, but doesn't let anything out. My understanding is that entire system is supposed to operate under a vacuum as fuel is removed from the tank. If one would ask the question "so why doesn't the tank pressure go up on that" I don't have a good answer. I don't know why your blower ends up in a puddle of fuel when you shut it off. And maybe even more important... I don't know why mine doesn't. Maybe because you're taking fuel out so fast? Maybe because the float chamber is atmospherically controlled? Don't know, and now it bugs me. Thanks a lot.

I haven't studied it, but off the top of my head I suspect it has mostly to do with "vapor pressure" and temperature increase. Vapor pressure is basically the pressure at which a compound will exist in both liquid and gaseous phases at the same time. In your gas tank, you have liquid fuel, and fuel which has evaporated into a gaseous phase. When that whole thing reaches equilibrium, the pressure in the tank will be the "vapor pressure" of the gasoline (at that temperature). I think the biggest contributor to the tank pressure is the increase in temperature as you drive the car. Most times you start it in the cool morning and everything is the coldest it's going to be all day. Then you drive the car and everything heats up. When the temperature of the fuel and vapors in the tank goes up, the vapor pressure goes up too. Exponentially. So, yes... You are taking fuel out while the engine runs. But I think the volume reduction (as fuel is removed) is a smaller contribution to the overall tank pressure than the vapor pressure is. Then when you shut the car off at the end of the day and everything cools off, the pressure will decrease and it will pull air in through the gas cap as necessary to make up the difference.

If the early rack is like my later rack, then you have to run the grease holes open. No plug. If you put a bolt in the hole, it hits the bronze bushing on the end of the rack and damages it. BTDT courtesy of my PO. I guess you could run some short set-screw plugs that ran in deep enough so they did not stick up proud at all. But since there's no pressure and everything is under a boot, I think you're supposed to just leave the holes open. Now... About while you are greasing the housing? I have no idea. My later housing doesn't have any facility to grease it.

Gary, that sounds perfect. It should be easy to blow air into the tank and difficult (but possible) to pull it out of the tank. Enjoy the whoosh.

The fuel issues with Gary's car are getting the fuel TO the anchors. The carbs themselves are working great. It's the supply that's questionable. We were out this afternoon for about an hour and it's running excellent even with the intermittent low fuel pressure. I think at this point we're just going to go for it with a couple contingency plans in place in the unlikely event that it gets worse. Murphy and all that. Looking forward to the group meeting of the Flat Top Advanced Research and Development Society. And I'm thrilled that you've worked out the bugs from your system. I'm a little put aside that you didn't reach out for assistance. It wouldn't have taken me two years.

Sweet! Looking forward to shaking your hand and buying you a beer.

I don't think even the BE section documents the color changes like the ones on that chime unit. I think the only way to figure all of those out is individual inspection of all the wires on the side of all the devices plugged into the harness. In other words.... No way. I think we all just have to understand the situation and why it is the way it is. I think now that we have identified the issue, it's not much of an issue.

Hmmm... I lost a post somehow? Thought I had responded twice, but only one of them came through. @Patcon That doesn't sound like fun. Do you think you may have aerosolized the plating while stripping it from the parts? And did your Dr. ask you about the metals first based on symptons, or are just looking for ideas?

I would have guessed cad, simply from the time frame involved. But it's simply a guess. So have you got any examples of the two that you could post as a pic? I thought they looked pretty much the same. Difference as was described to me was cad was a little darker while zinc was a little lighter and brighter.

Weird. No, I don't have an obvious answer, but here's some musings. There's no guarantee that all three cylinders fed from the same intake manifold get exactly exactly the same percentage of input stream, but they've got to be close enough to not result in that. All those Z's on the road running carbs with the stock intake... I'm no expert, but I've not heard a contingent of people complaining that the intake manifolds were designed such that 3 and 4 run twice as rich as the rest. Those clean plugs don't look like they've got anything at all on them. Like they're still brand new out of the box. After ten minutes or so idling, I would expect to see something on all of the plugs. I can't see anything in the pic... Is there at least something on all of them? Maybe the root problem is with the clean plugs, not the dirty ones? I would confirm that all the cylinders are firing (probably by pulling spark plug wires while the engine is running or some other potentially dangerous method). Pull and ground each plug wire in turn and verify that the idle RPM goes down and gets rough? Don't get zapped, and don't burn out your ignition system by running OC. I would also check the valve lash and run a compression test. Make a note not only of the final peak compression pressure, but also make note of (about) how many compression cycles it took to reach that pressure for each cylinder. If four cylinders take three revolutions to get to peak, but the other two take ten cycles, that could be a clue.

So trying to pull this back on target... Assuming we can shake down the bugs in our intended 260 ride and make it to the event without having to push the car, I'd be happy to demonstrate a set of flat tops on a stock 260 engine. The doubters can sit in the passenger seat with a big grin on their faces. This car was pulled off the road maybe twenty years ago, and has since been the subject to a significant tear down and rebuild of pretty much everything but the engine. It's seen maybe a hundred miles since being put back on the road. So what's the smart course of action? Jump in in and drive 2000 miles round trip, of course!!

As Henry McCullough once said (while talking about money) - "I don't know, I was really drunk at the time". You be the judge.

OK, fine. I put up a different pic.

Oy. Moving right along... Thats not MacGyver esque.

I can feel the flat top love from here. Getting stuff ready for the trip:

Hahaha!!! You've obviously seen my toolbox! So before this thread goes completely off the rails... Hopefully the fast track shakedown of our intended ride goes well and there won't be any pushing involved. Hope to see all of you soon! Friends old and new!

Ummm... Yes? You don't pay me enough to push.

So I had forgotten that I had these snippets from the FSM that relate to that check valve. Had posted them somewhere on some thread prior. Details have faded. In any event, mention of the check valve started in 76. I don't know if it existed in 75 and they just didn't mention it, or if it was a new device added in 76. Here's the location on the car: Here's how it looks in the system schematic. This is from the 78 manual. Previous years had a similar pic, but 78 is the most accurate: And here's how you are supposed to test it. Note that this test procedure didn't appear at all in the FSM until 1978. It describes a device which allows air to flow easily ("smoothly directed") from the carbon can back to the tank, but dictates that it should be harder to push air from the tank towards the carbon can. They say "considerable resistance" towards the carbon can. My interpretation is that "considerable resistance" could cause a woosh:

Nissan wasn't very good at labeling the wire colors on the device side for many of the small devices like this. In other words... I wouldn't be surprised to find that the wire colors on the harness side are correct on the diagram, and they were just never identified on the device side. I would guess that the creator @wal280z of that colored wiring diagram probably just assumed the wire colors did NOT change since there wasn't any info to the contrary. So... Is there a three position connector hanging down between the tach and speedo that has black/yellow, green, and black? If so, that's where that buzzer plugs in, despite the color change to a pair of reds and a black.

Yeah, me too. But it's consistent. By that, I mean, it seems to build up pressure to a consistent pressure and then level off. Based on that, I believe it's working. Well that, and my tank hasn't ballooned out from overpressure.

Second. On my 77 it is under the car close to the fuel pump and I would also assume that 76 is the same. That said... It's a check valve, but it will build up pressure in the tank until the "cracking pressure" of the check valve is reached. I don't know how big of a woosh you get, but I get a significant woosh on my car. And I believe it's working properly.