Captain Obvious

Gotcha. was just getting a little ahead of myself. So now the round tops are on and it's running OK. And your timing numbers are back to reality. Sweet! I fully believe that the carbs weren't the original root of the problems as all evidence points to ignition, but if you're happy with the round tops, it would be a completely academic exercise to find out for sure. Sounds like you're not that curious, and I don't blame you. I agree with your assessment about resale value and the round tops... Whether the flat tops reputation is deserved or not, it's just so prevalent and has existed for so long that there's just no way most people will ever believe otherwise. Without getting into the design details, I went back to the flat tops because I believe that the flat tops are inherently a better carb design than the round tops. IMHO, the single biggest advantage of the round tops is the ability to make large adjustments to the mixture by cranking the nozzle knob while the engine is running, and not only that, but you can do front and rear independently. The air bleed style mixture adjust on the flat tops works too, but it's range of adjustment is much smaller than the round tops which means that you must have everything else working just right, or you won't be able to get the flat tops mixture right no matter where you crank that screw. And you only have one adjustment for both carbs. Other reasons? I've made a bunch of improvements to my flat tops to improve some of what I consider shortcomings, and I have so much time invested that I refused to lose that battle. Also, there's some sick satisfaction in being able to make work what everyone else says is impossible. I assume it's the same thing for the people liking Gremlins or Azteks, dome houses, Brussels sprouts... An "underdog" kind of thing. All that and the simple "stockness" of the flat tops on my 74. Anything else in there just looks wrong to me. You didn't ask, but it makes sense to explain the other side of the question... "Why did I put round tops on then?" Because before all of my carb work, I bought into the "flat top boat anchor" hype and picked up a set of round tops. My flat tops clearly weren't working right, and I used the round tops to keep my engine running while my flat tops were under the knife, and also to see how my engine "should" perform with the "good" carbs on it. Kind of a baseline for proper performance. Now that I'm done, I think my performance is about the same between the two designs, plus I get all the improvements of the flat tops. It's probably off the direction of your original topic, but if you want details about design improvements, etc, LMK.

Yes, when he says "leaning out" he means that at certain RPMs and throttle positions (4500-5000 RPM and light to medium throttle position) his wideband indicates that his mixture is lean. Details are in post #229 (page 10), but here's the Reader's Digest version: You can see from the results that at the same RPM, he's running leaner at part throttle, than he does at WOT. The recent interest in ignition timing details isn't because it would do anything to add fuel to the mixture, but it might reduce the effect. In other words, the root problem is that he's lean, but it might be OK to be that lean, if it weren't for the fact that it's causing performance issues.

Cool, thanks. But when that shaft is installed, the gear on it meshes with another gear on the crankshaft, right? So then what is it that keeps the oil pump shaft from having to backwards drive the entire engine through the crankshaft gear while you're spinning it? Seems like a pretty heavy load on a shaft that small. What prevents you from turning the entire engine over with your handheld drill? What do you do? Pull all the plugs to reduce the load and just go ahead and let the engine spin? Still seems like an awfully large load for that shaft... I'm assuming I'm missing something simple here, but I don't see it.

I ordered a new oil pump a few days ago and I've been waiting for it to arrive. siteunseen, thanks for the recommendation for the Melling pump. While waiting, I've been thinking about that priming the pump process I've seen mentioned. Sounds like a great idea, but I've got a couple questions. I got the general procedure... Put the pump on the block and then spin the pump with a drill via the distributor hole. But... I'm assuming that the priming operation has to be done with the shaft between the pump and the distributor removed or the drive gear that normally spins the pump would try to turn the motor over, right? My shaft is currently out, but it came out the bottom with the old oil pump. Does that shaft have to go back in from the bottom, or can I slide it in from the top after the pump is bolted into place?

Excellent! So it's working well with the flat tops and as soon as the round tops are done, you'll toss those on and see how they work? Here's a starting point for you... The flat tops are the same thing as round tops with the nozzles three turns down and then an air bleed around them to lean the mixture back out some. Keep that in mind when you're tuning the round tops. If you find you need three turns or more down to get it to run right, you've most likely got a vacuum leak somewhere. First time I tried this swap, I reused the same insulating spacers and associated gaskets. Problem was, however, that the bulges in the gaskets from the water passageways in the flat top carb bodies didn't seal perfectly against the round top bodies. It ran OK for a proof of concept test, but I needed more turns than I should have to account for the extra unfueled air leaking past that insulator gasket. So, the next time I had the round tops off, I replaced those gaskets and everything got better. Then the next time I had them off, I pulled all the studs and replaced with longer and went with the thicker insulators and all new gaskets. Then, I pulled it all back off and went back to the flat tops. I've not yet messed with the ZX ignition module, but I've heard good things about them. Mine (fingers crossed) seem to be working fine and I'm inclined to leave sleeping dogs lie. So... Are your timing numbers back to reality?

In my opinion nothing is less appalling than a vinyl top on a Z.

Wait..... So does that mean that the problems you were having have been fixed? It was an ignition problem? Haha! Nice. Yeah, my modified round tops turned out pretty well. I bought a spare set of flat tops and they were damaged in shipping so by the time they got to me they were parts only. I didn't feel too bad about them giving their internals in the name of experimentation.

knarfrabot, Here's some pics of the glove box lock, so you know what you're up against. Looking at the back side (inside the glove compartment side) it's clear that you would have to pull down on the latch to open it, not push up as I suggested before. It looks like coat hanger wire with a little hook on the end should work great for this. Hope this helps! Glove box lock: Cylinder with no key installed: Cylinder with correct key installed: Inside of the lock shell with cylinder removed:

Unkle, I agree that picking that simple lock would be child's play, and a lot better of a plan than prying or drilling. However, before he feels he has to resort to any of that... (prying, drilling, or picking), I offered up what I believe to be other completely viable options for him to try first. My point of contention was that I believe the suggestions I provided were, informed, thoughtful, non-destructive, and wouldn't cause any more damage to anything that hasn't already been done, and best of all, they are instant and free. It was an opportunity for me to give back to the forum for some of that which I've gained, and it was an attempt to share some of my recently acquired detailed knowledge of the inner workings of the Z locks with a fellow forum member and try to help him out of a jamb. What got my goat is that my informed, thoughtful, non-destructive suggestions were being cast aside as improper, damaging, low quality advice. That's what it sounds like to me when you call my suggestions shade tree advice and tell him "the right thing to do is let a pro deal with it !." I should be better than to react as I did. I should have just let it go, and I'm sorry that I did not contain myself.

Exactly. That was what I was thinking with one of my suggestions. I didn't remember for sure if you could easily get at all of those retaining screws with the door shut, but if you can that would be easy. Then once the door is off and he's out of the woods with his immediate crisis, he could decide how to proceed from there.

All the shade tree advice? Seriously? Simply because it's your field of expertise? All shrouded in magic and mysticism? My suggestions were non-destructive. I don't think he should drill it out either, and before he gets to that point he should seek help from a professional. But he's not there yet. Sure, if you want to and think you have the skills, you can: change your own oil, or unclog your own bathroom drain, or put on new brake pads yourself, or cut your own grass, or replace your own spark plugs, or wire your own stereo, or change your own light bulb, or paint your own kitchen. But don't mess with your own locks... There's professionals who do that. :disappoin Heck, I've even heard of people who aren't mechanics rebuilding their own engine. Or people who aren't electricians putting in a new outlet in their living room. Shhhhh... Even non-carpenters putting up sheds in their own back yards with no official training or certificates at all! Oh the horror! Wow... My other lock thread must really bug the crap out of you.

Or... If you're really really sure that you will never be putting the flat tops back on the car, you could do what I did with mine. Here's round tops redressed with flat top throttle shafts. Took some machining work, but now they're a direct plug-n-play drop in to where flat tops normally live. Integral return springs and all: Thanks for the tips on the thermo switch. Surprising, but I hadn't considered trying to take it apart. I never imagined there could possibly be anything salvageable in there. I must be slipping. I did looked (briefly) into a replacement, but didn't turn up anything good. The newer ones for the 280 are cheaper and plentiful, but they are backwards acting compared to the earlier years. I considered using one to actuate a relay to reverse the logic, but all of that is low priority. Once my engine is up to temp, the switch works just fine.

I've got all the locks from my 77 torn apart right now, and my glove box was keyed the same as the rest of the locks on the car. I would assume the 78 was done the same way. Are you sure the glove box is supposed to take a different key? Maybe the key is just worn? Regardless... Two suggestions: 1) First suggestion is that you put the same key you used to lock it back in the lock again and wiggle it around while you gently try to rotate it clockwise to unlock it. Try to angle the key tip to the right by pushing the key head to the left as you turn it. If that doesn't work, try the opposite... Try to angle the key tip to the left by pushing the key head to the right as you turn it. 2) I didn't try this, but maybe you could take off the three (maybe five?) screws that thread into the dash that hold the glove box door on? That might enable you to get the door loose enough to reach all up in there and manually push the lock catch up and open the door with the lock still locked. Maybe a long screwdriver and a flashlight while on your back with your head in the passenger footwell? Seems it wouldn't be a very secure lockable compartment if it was this easy, but you never know.

You probably know this already, but when you put the round tops on, your original center linkage between the two carbs won't work anymore. You'll need to swap over to the round top center. Also, you'll need to fashion some kind of return spring and figure out means to hook it to the heat shield because the round tops don't have integral return springs like the flat tops do. You can use your original flat top heat insulator blocks between the carbs and the intake manifolds, but most people switch over to the thinner square style that came with the early round tops. If you switch to the thinner ones, you'll need to pull all the studs and replace with shorter because the longer ones that work with the thicker insulator will now be too long and will hit the round top carb bodies. What else? You mentioned above that you wanted to keep your EGR... I guess you could hook your EGR control solenoid valve to the port vacuum source on the front carb (the same port that supplies the vacuum advance signal to the distributor). The rear round tops don't have any vacuum nipples on them at all so you'll have to route to the front carb to retain some sort of EGR control. The port signal from the front round top is a little different in design and location than the port signal from the rear flat top, but it's the closest thing you'll have available once you swap round for flat. Good luck and if there's questions about what hoses do what, let me know. I (unfortunately) know what each and every hose in that bundle of snakes does. PS - Your round tops are probably not real "Skinners"... They're probably Hitachi.

So you're thinking that your problems started up top? Did you see my reconstructed spray bar on my 74? Way overengineered, but I'm very pleased with how well it turned out. Here's a thread about it: http://www.classiczcars.com/forums/showthread.php?44750-Camshaft-Oil-Spray-Bar-Redesign-and-Rebuild The oil pressure on that 74 is fantastic. Unfortunately, my 77 is the one that's currently giving me troubles and it's got the internally oiled cam setup.

Lazeum, Thanks for the additional info. I read through your HBZ topic and I hope that I won't have to dig in as deep as you did. I've got a question though... I'm not sure I understand how the cam and rockers could end up taking damage from debris when the oil filter is supposed to catch that stuff. I could maybe see something in the lower end picking up a chip right out of the oil pan since everything in there is swirling in unfiltered oil, but even if some debris passes through the pump, shouldn't the oil filter catch it before it ends up in any of the bearing journals? Is it possible that your upper end issues weren't caused by debris, but were caused simply by low oil pressure that occurred when the pump stopped working? Or am I just putting too much faith in the effectiveness of the filter? :disappoin The chips I found were non-magnetic, but that doesn't mean they are the only ones that were involved. By that, I mean, the non-magnetic chips may be pieces of aluminum that were scraped off the inside off the oil pump body as something magnetic got pulverized and eventually passed through. No problem! It's nice to see current owners and previous owners happy with eachother.

I had the camera out so I snapped some pics of my original oil pump: Not sure what it ate, but it's obvious that something went through there that shouldn't have. :sick:

The reason I was asking about the RPM while timing is that I'm wondering if the wacky numbers you're getting are partially caused by the vacuum advance. The vacuum advance signal comes off the front carb, and it's a port driven signal which should be zero at idle, at it's highest vacuum a little above idle, and then fall off from there as the engine load increases and manifold vacuum decreases. At 1250 RPM, it's a toss-up if you're still running on the idle tubing feed to the balance tube or not. At idle, your flat tops should be dead against the factory set linkage stops on the front (radiator side) of each carb. The epoxy plugged Phillips head screws that the manual warns you not to mess with? You're still up against those stops at idle, right? I'm assuming when you said "TDC verified on the dampener" that means that your manually rotated your crankshaft until you had #1 piston at TDC and then verified that the timing mark on the dampener was in fact in lined up with the "0" mark on the timing gauge. Is that correct? So it won't even run at all unless your idle timing is set somewhere above 20 degrees BTDC. That's just not right.

Now who in their right mind would do such a thing? Don't people have better things to spend time on? OK... So I just went out to the garage and snapped a few pics from my collection: Purolator L10241: AC Delco PF1127: Note the separation at the seam where the original filter media was never glued properly at the factory: Here's a closeup of the seam separation: I used to be sold on AC Delco until I opened this one and discovered the open seam in the filter media. Then to make matters worse, they've since changed their internal construction from a metal support structure for the filter to a plastic cage. To each his own, but my current fave is Purolator. Anyway, good idea Bonzi. It would be prudent to open the one off the 280 when I get to that point.

Exactly. That's The Plan. Fingers crossed and all that. :paranoid: The only shavings I found in the pump were small slivers visible with an eye loupe (maybe 10X). There were no big chunks. What I found was small bits pressed into the gouges that were left in the rotor from whatever went through there. Think fillings in a tooth cavity. The previous owner did a rebuild of the engine, and from all I can tell, he was very good at cleaning. I'm not sure yet about other aspects of his rebuild, but I'm confident that he cleaned everything very well. In other words, I bet he cleaned out the pan and screen already. Hopefully this will be as simple as a new pump, and I think I'm going to change the oil and filter even though it's fresh. If that doesn't take care of it, I'm going to have to get into it way deeper.

Yeah, I've been all through the ins-n-outs of the power valves as well. Dug out the epoxy and played with the screws and all that. The reason I took mine off was that I was running very rich and I wanted to eliminate as many variables as possible. Then once I had them off, I realized that my car (other than foot hard on the floor) runs pretty good without them if you use the right needles. I mean, after all, without the power valve, the flat tops function exactly the same as the round tops. I tried round tops as well, and my performance was identical. YMMV. As a matter of fact, I modified a set of round tops to be a direct drop-in to my 260 so I didn't have to muck around with the round top linkages and return springs hooked to the heat shield. Granted, the extra idle tubing is a little cumbersome with the flat-tops, but there are advantages in that as well. The engineer in me sees the beauty in the functionality. But we're getting a little off course here with all the flat top talk... So, the bottom line is that unless there's some interpretation discrepancies on what your car is doing, I don't think round tops will solve your problem, but it will certainly simplify the engine compartment and hopefully make the problem easier to find. The timing issue is really perplexing... What RPM is the engine spinning while your setting the timing? Is it as a "reasonable" idle speed (like below 1000 RPM)?

Yes, the FSM has some pics, but they're lacking in detail and it's hard to figure out what's what. Here's one from the 72 manual, and another from 77. Only reason I know that the distributor shaft and drive gear are unfiltered is from looking at the pump design iteslf.

Thanks Jeff, I appreciate it! I'm hoping for the best. On that subject... Do you know off-hand what is lubed pre-filter? Just the distributor shaft and oil pump itself? Everything else is post-filter?

Well I still can't explain ON-OFF shuddering with any carb problem. Especially since you've got the correct fuel level in the bowls. I know from experience that once my bowls are up to the proper level, my car will idle for maybe 30 seconds to a minute or so with just the fuel that's in the bowls. And the when it finally reaches the point where the fuel has been sucked down to the point where the nozzle just can't pick up fuel anymore, it sputters a little bit until it just can't sustain running any longer and finally stalls. In other words, even under that situation, I get a slow painful gradual death. Not a "lights out - no wait... lights back on... lights out again" kind of thing. Once you've got fuel in the bowls, you've already made it past the smallest of the orifices. The fuel is pretty much home free by that point. I dealt with my power valves by eliminating them and I do think I'm a little lean at WOT because of it. I'm running early round top needles in my flat tops because they're a tiny bit richer, but not enough to make up for the loss of the power valve at WOT. The car starts instantly and runs great and if I put my foot to the floor, it doesn't fall on it's face, but I think it should go a little better. So again, like my plugged EGR port, it's a lower priority for me right now. What makes you say you need new floats? You mangled them a little trying to get that $*%@#@#$ float pin out?

Funny you mention that... Mine looks like shavings were forced through causing damage in the form of dents and abrasions in the rotor and body. :laugh: I didn't even bother to measure anything. I'm assuming that something grenaded inside the engine at some point in the past before I owned the car. Under magnification I was able to pick out some small chips that were still embedded in the rotor assy. I don't know what they were from, but I can tell you that they were non-magnetic. Probably aluminum, so best case is that they were material torn off from inside the pump body itself. It's pretty gruesome. So, I understand that the oil pump might not be the only problem, but after seeing inside the pump, it's clearly at least part of the problem. At this point, I'm hoping that any debris that made it through the pump got caught up in the oil filter and my "plan" is that a new pump will take car of it without having to rip the whole engine apart. I've not yet even had a season of enjoyment out of this one yet! The PO did a rebuild on the engine shortly before I bought the car, and although I'm always skeptical of anyone's work other than my own, I'm inclined to believe he knew what he was doing. Curious though with all the money he spent on the motot that he did not replace the oil pump. Anyway, used cars are always a crapshoot. I'm hoping that a pump will fix it, but I'm aware it might not. Brand independant? No-name ebay is just as good as genuine Nissan? Anything from RockAuto is good too? And SteveJ, those search results are light-years better than what I could turn up. Thanks for the tip.