Captain Obvious

Sorry, but nope. Manifold vacuum never pulls the piston up. The vacuum that pulls the piston up is on the wrong side of the throttle plate to be considered manifold vacuum. The reason the piston drops when you decelerate isn't because the throttle plate keeps the manifold vacuum away from the piston... It's because when you decelerate, there is very little air flowing through the carb. The pistons lift based on airflow. The more air volume that flows, the higher the piston. The less volume that flows, the lower the piston. And when you are decelerating with the throttle plate closed, there is very little air flow volume. I'll dig up some theory of operation documents for the SU's, but I suspect Blue has several at his fingertips. I might just stall for a couple hours and let him post 'em up. I'll let him get into all that Bernoulli stuff. And as for your idea about measuring using a magnified picture... That's a great idea, but someone beat you to it. It's called the "Optical Comparator." You put the part in question on a table and a picture of the magnified part is projected on a screen along with calibrated dimensional lines for measuring. http://en.wikipedia.org/wiki/Optical_comparator I've toyed around with the idea of getting one for my shop, but can't justify the cost or the space it would take up. In the meantime, I'll just have to resort to my calibrated Starrett, my good eye (with magnification) and my steady hands. So you want to send me your N-27's for me to add to my catalog? I'd love to double my sample size!

Yeah, I've done that kind of thing at times, but I really don't like to. Especially for larger wire sizes. I don't mind so much crimping two 20 GA together, but much bigger than that and I don't like it. So about adding completely new wires... On the 4 relay design, I did add a new R/B wire from the relay block out to one of the headlights. The original system daisy chains the filament currents together, but with one relay for each filament, you can't do that. You need another wire run to the front for one of the low beams. The two relay hybrid version shouldn't need to do that however. You'll have both sides HI beams running through the R/W (the largest wire) and both sides LO beams running through the smallest R/B (just like stock).

Yes, the fourth relay is different than the other three. That's why I was saying that three out of four of them are very easy to find (eg they are the same ones used in the Honda relay block I used), but I wasn't sure about the fourth. It might be a very common one as well, but I don't know. I stopped investigation when I went with the Honda block instead.

Hmmm... I'm not sure I'm understanding what you meant, but I didn't have to pull any new wires through the firewall: Original Red from the fuse box for power to right bulb relaysOriginal R/Y from the fuse box for power to left bulb relaysOriginal R/B for low beam actuationOriginal R/W for high beam actuation That's it. The branching for different relays I did out in the engine compartment inside the harness stem to the relays. For example, I needed two R/B wires to control two relays so I spliced a second R/B onto the original one that came through the firewall. Same for the power wires to multiple relays. And since only one of them is carrying any current at any given time I feel completely justified in that. So, yes... I did need extra wires, but I did the splitting inside the harness on the way to the relays. You could, if desired, make all the splitting connections by crimping multiple wires into the relay spade connectors and daisy chaining them using the crimp contacts as your junction points. I didn't do that because I didn't want to complicate the crimps, but that could work as well.

At the risk of telling you stuff you already know, I'm not sure you understand the suction piston operation... It's not pulled up by manifold vacuum. It's pulled up by the vacuum difference between the mouth of the carb and the area right behind the suction piston. In other words, not the area on the engine side of the throttle plate, but the area just BEFORE the throttle plate. The suction pistons don't operate by manifold vacuum, they operate by airflow speed through the carb. The more airflow through the carb, the higher the vacuum just on the downstream side of the piston and the higher piston is pulled. The intention is to keep the air speed through the carb venture the same regardless of how much air is being pulled through. That's the "Constant Velocity" part of the "CV" operation. So with that in mind, when you goose the throttle, the piston won't fall but will be pulled up. Quickly. Too quickly in fact! And if you pull the piston up too quickly, you'll run lean during that transition and sputter when you increase the throttle position (Kinda exactly what you're describing). That's why there exists the whole damper stalk and oil in the pistons. To slow the rise of the piston when you nail the throttle. So I agree that it sounds like you're running lean on transition, but I would start by looking into your damper oil level and viscosity or the operation of your jiggly bits on the end of your damper stalk. Those jiggly bits are a check valve intended to slow the piston rise but allow fast decent. I've seen more then one occasion where those little jiggly bits didn't work properly resulting in a lean transition situation. And as for your caliper, I'm not poopooing the idea of you buying a good Mitutoyo. I think it's a good tool choice. Go for it! Just don't try to use it for needle measurements.

Yeah, I understand. I've found the easiest to harvest is from the 98-00 Civics, but they are on other Honda derivatives as well. Good luck with the hunt!

Here's a snipped from the FSM on which I've made some notes (in red). Might help to determine if it's a wiring issue or a tach issue?

I'm no engine builder, but I'd have a hard time closing that thing up knowing I had pistons that looked like that...

I'm not sure I understand MSA's comment either. The original nozzles should fit fine with any 0.100 needle. I've heard the comment about the SM's being way leaner at idle, and I disagree. It might seem like that at first glance when you look at the numbers, but don't forget... You never ever use station 1. The nozzle adjustment nuts are M10 x 1.0 thread, so at your standard 2.5 turns down, you're already at least .098 down from station 1. Then you consider the fact that even at idle, the suction piston is pulled up a small amount and you're very close to station 2 if not past it. At station 2, you're a little leaner than stock, but by the time you get to station 3, you're already richer than stock. The transition point is somewhere between 2 and 3. In other words, I would expect the SM's to be pretty much identical at idle and get richer from there. I'm no carb expert, but that's my read. As for the needle measurement method, I don't think this is a job for a caliper. Too springy... I think a good micrometer with a ratcheting knob (for repeatability) is a better tool. I used a Starrett on which I had just checked the accuracy, and I did it all under magnification. Even so, It takes some technique to get repeatable results. But as for your HF caliper, I can't imagine it's so bad that it gave you trouble reverse engineering pallet racks. I gotta believe that's far enough from rocket science that you could probably get away with just a scale! I would have expected the HF to be at least accurate to +/- .004"... That has to be good enough for a pallet rack, right? I looked a bunch for the specs on the N-nn needles and came up blank. I suspect the reason is that they were custom made by Hitachi for Nissan. In fact, I'm thinking that might even be what the "N" stands for.

Funny you should ask a question about that... I nabbed these relay/socket assys from Honda/Acuras. I found them to be very compact, orderly, and gangable. They also use a very ubiquitous relay style that you can find pretty much everywhere: . I just posted a bunch of other details and pics in thread about my headlight upgrade experience: http://www.classiczcars.com/topic/51554-a-different-headlight-relay-upgrade-4-relays/

Here's some info on the relays I used for my headlight upgrade. The relays themselves are used in lots of applications and are easy to find, but what really grabbed me about these isn't the relay at all... It's the socket. This relay/socket combo is used in lots of Hondas and Acuras (For example, All 98-00 Civics have at least one assy and two if it has a sunroof). They come in SPST and SPDT applications depending on the original use (for example, horns use SPST and sunroofs use a pair of SPDT). They are easy to harvest and can be found under the left side dash near the driver's left knee. Some models only have one position populated, but have a socket that will accept two relays. Depends on whether it's a manual or auto. And cars with a sunroof will have a second socket (with SPDT relays). Here's the socket and relay combo I used. It's small, comes with a mounting bracket, and accepts two relays: Remove the relays and you're looking at this: What I found really useful about these sockets is if you strip down two of them like this: They gang together!!! So if you need more than two relays and want to mount them all in the same place: Put in four relays and you got this. It's much more compact than the "Bosch style" relays: Since I had just completed an internally regulated alternator as well, I put my headlight relays in the spot vacated by my original external voltage regulator: On the last pic, you can see the retaining feature on the end that makes them gang-able. It really helped simplify the mounting and kept the size as compact as possible.

Yeah, there's some significant differences there. Could be measurement tools, technique, or both. If you're sure what you have are stock N-27's I'd be more than happy to check them for you. Send 'em over, I'll record them and send 'em back. And BTW, I'm pretty sure it was just a typo, but when you said .010", I'm thinking you actually meant .0010", right?

So they sent you that rusty head claiming that it was a good condition usable piece? Seriously?

So were your numbers anywhere close to mine? Or are you in the market for some better measurement tools?

There's no way a digital HF caliper is going to cut it. The resolution is only a half thousandth, and the accuracy (and that's advertised accuracy) is one thousandth. It's good enough to toss in your tool bag to take to the junkyard and tell the difference between a .68 wide rotor and a .72 wide rotor. Not nearly good enough to take measurements off the needle stations however. A couple years ago, I measured some (what I believe are) N-27 needles. They came out of a pair of round top carbs I bought. I didn't own them from new and I have no idea how many other hands had been into them messing around with things. I may have been the first person in there, or the tenth. The needles may be OEM stock, or may have been replaced and changed many times. And unfortunately the numbers on the side of the needles is no longer readable. What I can tell you is that the carbs appeared to be unmolested and the needles are N-somethings printed in black ink (not stamped into the brass). I can also tell you that the car I had the carbs installed on ran great with those needles. Not too rich, not too lean. The carbs worked great. Bottom line is that I believe, but cannot guarantee, that they are N-27 needles. Lastly, I have a good eye, a steady hand, and made these measurements with a quality micrometer. I'm not infallible however, so would I would claim accuracy only to maybe plus/minus maybe two tenths. So with multiple qualifiers and caveats, here are my numbers:

I checked and double checked. My 77 uses three different gauges all the way out to the bulb. Like I said though, I don't know what other years did. Those grommets are actually Mitsubishi power antenna drain tube grommets. Find one on an Eclipse or Diamonte and probably other Mitsubishis as well. I grabbed three of them last time I was at the yard. One for each headlight bucket, and one (you guessed it) for my antenna drain! I think it was a little tight to get into the antenna hole in the body, but once it's in there it's snug and certainly way better than the dry rotted non-existent grommet that was in there before. I put a small ty-wrap on the antenna tube as well just to make it as well sealed as I could. Anyway... I'm getting off topic. Back to the headlight buckets. I cut the holes on the back of the buckets large enough such that I could get the connector off the back of the bulb and get the connector out through the hole from the rear. And your question about the H4 bulbs is exactly why... At some point, I'm thinking that I might upgrade to H4's and it would sure be nice to be able to get the bulb out the back as well without having to drop the buckets. So, the bottom line is that was my intention, but I haven't tried it. Hole might not be big enough.

Well I'm not sure if they ran different gauges for different years, but on my 77, I've actually got three different gauges running the whole way to the bulbs. Including the little pigtail between the buckets and the harness. I modified my buckets for a new larger grommet so that I could take the connector off the back of the bulb without taking the whole headlight bucket off the car. But the point is... You can see the three different gauge wires: The red/black for the low beams is the smallest, the red (common) is larger, and the red/white for the high beams is the largest. Note that I've got my red/white wrapped with black electrical tape stripes to remind myself that it's actually the common now and connected to ground instead of it's original connection. And in case you're interested to see what the grommets look like once installed in the back of the buckets:

Tamo, I whipped up a quick sketch for the starter relay. Original design is on the left, upgraded version with the new relay is on the right. Basically you are reducing the loading current on the starter switch so you don't burn up the contacts inside:

I'm assuming the "Bosch style" is a term coined by automotive enthusiasts to describe the size, shape, and pinout of those relays. I'm not sure Bosch ever really actually made relays themselves. If forced to guess, I would assume that Bosch didn't actually make them themselves, but private labeled them from someone else and had Bosch screen printed on the case. There may be some small spec variation in the part specially for Bosch (or maybe not). There are lots of relay manufacturers, and I don't think Bosch would compete in the world market. As far as being inferior goes... About the only words of advice I would provide is buy from a name you recognize. And even then (as Blue has pointed out on numerous occasions) you're not always guaranteed to be getting what you think you are. On the good side, however, you're not going to be taxing these relays anywhere near their max specs, so even if they are a little sub-par, you'll probably be asking them to perform below what they can handle.

Great. That'll provide a source for others. Getting the contacts out of that spade connector body is pretty easy. If you managed to get those contacts out of the Ford O2 sensor, then getting the contacts out of that six position spade connector will be a breeze by comparison. Paper clip, jewelers screwdriver, small piece of stiff wire. You can even see the retaining tang without magnification.

Tamo, Three of the four relays in that Corolla box are very common and are almost as ubiquitous as the Bosch style relays that you are using. Here's an ebay auction for the three common ones. This one happens to say Toyota on the side, but there are lots of manufacturers for this one: http://www.ebay.com/itm/TOYOTA-Fog-Light-Relay-Fuse-DENSO-12v-OEM-Factory-90084-98031-/111438776950?fits=Model%3ACorolla&hash=item19f244ca76&vxp=mtr I'm not sure about the fourth relay. It might be easy to find as well, but I've not looked into it. So yes, I can guarantee that three of the relays are very easy to find replacements, but I've bot looked into the fourth. About the open barrel contacts, Do you know how the retaining feature works on your relay block? There are a couple different retention schemes used, and each one has a different feature on the contact that is important. Some use a little bent metal tang on the back of the contact, while others use the plastic tab that catches between the two rounded portions of the contact. Without knowing how your contacts are retained, I'm not sure I can help with a source. And as for a starter relay, it's different than the ignition relay. It's an additional relay upgrade (like the headlight relays) to add a relay where there didn't originally exist one. I searched around thinking I would be able to find a schematic that someone already drew up, but couldn't find one. I'll draw something up when I get a chance, or maybe someone else knows where to find a sketch and can point you to it. Essentially, there is a black/yellow wire that comes off the back of the ignition key switch and goes to the starter. Problem is that the starter draws more current from that wire than the switch likes, and eventually the switch stops making contact. The solution is to add a new relay between the switch and the starter.

Thanks Chuck. I've been concentrating on reliability and just getting stuff to work properly, but one of these days I should try to make my Z look better.

Tamo, I'm not sure how the terminals are retained into the box you have, but most of the ones I've investigated use a little clip that catches on material between the two rounded bent over "wings" on the spade terminal. The reason I bring it up is if you try to use a terminal with too wide of a gap between the two sides, it won't catch the retaining tab. I've had a little trouble sourcing open barrel female spade contacts that have an appropriate spacing. So I don't know if your box even uses the same retaining feature, but I hope your contacts work properly. If not, I can dig up the info on what I purchased. PS - If you've got an extra relay in your box, I would suggest using it as a starter relay. Put it between the ignition switch and the starter solenoid instead of having the ignition switch drive the starter solenoid directly. The current to drive the starter solenoid eventually burns up the contacts inside the ignition switch and putting a relay between the two will prevent that from happening.

Tamo, Glad to help. And on a related note, I was at a junkyard today and snapped some pics of the Corolla relay box in it's natural environment: The one I saw today was a 98 Corolla but I'm sure the used the same box on all years of that generation:

That concept has been around for quite some time: