Stanley

Did you install the dual point with one set of points removed? Sounds like the engine's happy, anyway. Wish I could run 17 deg. As I recall I couldn't get it there even with the stock head. With higher compression and California gas, it pings at more than 10 deg. Maybe all 260's have electronic ignition? If so it would need to be hooked up per '74 FSM.

Doubt if removing one set of points would work but I don't know. Why not just order a rebuilt single point for a 70-72? It's about $100 USD. A-1 Cardone part 31-607 for the US spec., but if you get one from your local auto parts store I'd think it would be the Euro spec. model. A new Hitachi Euro spec from Japan costs $650 USD here, so if you get a rebuilt one and it's Euro spec please post the information. Maybe Nissan dealer in Europe can get you new factory one.

You don't want that dual point distributor, expect hard starting, reduced performance, and an insanely difficult process to set dwell and timing. Easiest is use '70-72 new (from Japan) or rebuilt single-point, Euro-spec distributor. Single- point emission spec OK I guess. Or go electronic.

Shouldn't need to torque them down that much, if so the washers are bad or wrong, or else there's an imperfection on the mating surfaces. Had to polish mine with 600 grit wet/dry sandpaper and use new washers, after that normal torque was OK.

Keep a fire extinguisher handy if you do that. FSM says max fuel pressure for SU's about 4.3 psi. 9 psi is more than double. Too much fuel pressure can overpower the needle valves and cause the float bowls to overflow.

The water pipes are the supply and return for the manifold heater system, that circulates hot coolant through the intake manifold to warm it up in cold weather. It's supposed to have a hot = closed thermostat (so it shuts off when the engine warms up) between the rear of the intake manifold and the metal tube that goes around the rear of the engine, maybe it's there but I don't see it. It's probably good to have in cold weather. Problem with it is the tube that goes through the manifold gets rusty and leaks. The air galley, that rusty pipe that connects to each runner on the exhaust manifold is the most difficult piece to deal with. Mine was leaking exhaust fumes everywhere, had it removed and the holes in the manifold welded up. There are other, more technical solutions that are nicer, search the site - there are photos of how others have done it. The metal tube that's hooked to a tee (other side goes to the brake booster) is attached to the AT modulator on the transmission (with a crappy old 2" rubber hose that needs to be replaced if not done already, otherwise it will fall off and you'll think the tranny is shot). The AT won't work right without it. The rest of those antiques can be trashed in my opinion, no place for them on the Euro balance tube anyway. What is all that stuff?

Right, need a red spring and a new #23 side by side for comparison. That PDF on link I posted in #26, is from 1968, and does not have a number of needles that were added after that. For example, the BCA, BCE, and BBZ needles that SU recommends for 240z (according to source quoted on zparts.com) are not on that list. Some interesting tuning ideas, though, and nice picture of mechanic listening to carb with rubber hose. Wonder if the #23 Hitachi SU springs are NLA. I'd guess the SU's for roadsters and 510's used different springs since they used different needles, which might confuse the issue of part numbers. It might also help to measure an N-54, stock non-emission needle for the '72 three-screw carbs, for comparison.

Found this for springs: Yellow (AUC1167)8 oz.@ 2.750", Red (AUC4387)4.5 oz.@ 2.635", Blue (AUC4587) 2.5 oz. @ 2.625". From official SU handbook that I couldn't print from. Also found this PDF, with full needle profiles, kind of old but probably haven't changed or added new ones:http://mgaguru.com/mgtech/books/pdf/Tuning_SU_Carburetors.pdf There's the SU "Needle Profile Chart" on SU carbs site. Couldn't find a PDF anywhere. Not expensive but looks like you have to order it from England. Compared to your calcs for stock springs: K yellow = 8 oz. / 2.75 in. = 0.18 lb/in = 2.91 oz/in K red = 4.5 oz / 2.635 in = 0.11 lb/in = 1.71 oz/in K blue = 2.5 oz / 2.625 in = 0.06 lb/in = 0.95 oz/in Looks like red springs are about stock, blue for performance (with richer needles only, otherwise worse), and yellow for super gas mileage and poor performance.

Black Dragon. Get the best one they have, cheaper in the long run.

Have the video, haven't watched it for a couple years though. Good stuff. IIRC there's a shot of the carb pistons in action. The pistons seem to raise and fall at the same rate. Made sure, last time the air cleaners were off. Modifying the N-27's made a big difference, tuned out most of the miss, We'll see. Wondering about the springs. I see 8 oz. (yellow), 4.5 oz. (red) and 2.5 oz. (blue) are available. But FSM says stock springs are #23's ? I'm might try a set of 2.5's but wonder which ones if any are stock. Bottom end of my engine is stock, top end and exhaust not so much. 2 1/2 turns down was OK (as was regular gas) until I put the '81 JDM head assembly, guess it flows more air.

I've tried the choke test a few time but it was inconclusive (so I'll try it again). It helped but there was still some weakness. Last time I changed needles and tuned carbs, I was refilling the dampers and noticed one piston was easier to push up than the other. When I put more oil in that one it was harder to push. By adjusting the oil (apparently), I got both pistons the same. Looking at the drawings, though, I can't see how that would work. Maybe something else affected it, like one damper stalk not being screwed down tightly. Maybe the oil is too thick for the richer needles. When I said it was too lean above 4 turns down I don't mean it was lean overall, just that leaning out on acceleration was worse. I have flexible tubes for the sight glass, so I hold them right in front of the nozzles to check, which eliminates effect of different fuel height in front and rear bowls. Fuel level is high but not pooling on top of nozzles. My sight glasses are leaking slightly at the tube fittings so I need to fix that before doing the shut-off test.

Under load. Revs fine at idle. Accelerates fine at part throttle. Was better with modded N-27's than the SM's in there now. The N-27's have been re-polished and will go back in as soon as I get a break with the work. Making plenty of torque with SM's but have to be careful how I drive it. Using heavy 30wt oil. Adjusted amount of damper oil so each piston is equally hard to push up. Fuel pressure steady about 3.9 psi all conditions. Fuel in bowls set slightly higher than stock, checked with sight glass. Running too lean unless it's 4 turns down. 1/4 turn more and it fouls the plugs. Exhaust feels smooth, but it sounds slightly heavy like it's on the rich side. Passes the paper towel test though, except when I first start it up. The link's not working for me.

I have plans for those particular stock N-27's. Going to do some experimental mods on those when I put the professionally modified (now re-modified) N-27's back in. Don't want to accidentally mess those up, since they work, if not perfectly. However I plan to buy a few more N-27 in the near future, also some more SM's or other British needles. Been reading Des Hammill's book, way over my head at first but I'm learning. He explains in detail how to modify SU's to equal the performance of Weber's or Dellorto's, but it's not quick or easy. Needles are (almost) everything. I see now that manifold vacuum relation to piston height is anything but linear. Seems proportional though; but that ratio varies depending on throttle opening and also on piston height. At high RPM with WOT, seems like the suction on the piston is proportional to manifold vacuum, since the Bernoulli effect is minimized due to high piston position. Hammill talks about two ways (not including WOT at top end) a lean miss occurs on acceleration. First, the piston rises but A/F ratio can't keep up; this can be tuned out with damper oil and/or needle modification. Second, as the throttle is opened, A/F leans out and the piston will not lift because not enough suction is generated by the engine (Hammill, p. 20). This is tuned out by modifying the needle. Simple in construction, not as simple in theory. I need to think about this some more. All I know for sure is that when manifold vacuum drops below 5 in/hg at WOT, it misses or pops through the carb. I was hoping I pull the air cleaners, try to get it to idle at 5 in/hg, mark the needle position and polish them down at that point. That idea is probably toast.

Plenty of stuff I don't know in SU hot rod school. Anyway, I'm starting to understand why I was wrong about piston position varying linear with manifold vacuum. It was hard to understand until I thought about deceleration. In that case manifold vacuum is at it's max, but throttle is closed and the piston drops because the closed throttle keeps manifold vacuum from pulling it up. Right so far? Seems like needle dimensions could be accurately measured with a photo. Take a hi-def photo of the needle from an angle that minimizes distortion, import the JPEG into paint or similar, make a large bitmap image and copy into a CAD program. Blow it up as big as possible without blurring. Measure the needle length with micrometer, drawn a line equal to that length (or say 100 times the length if that helps resolution) on the image, and pull the image in or out until the needle length matches the line. Trace the needle image with the CAD. Draw 1/8" stations on the traced image, set dimension accuracy to 0.001 inch and dimension them. Move the image out of the way and there's an accurate (enough) diagram.

I think the problem with the SM's, at least in my case, when you hit the gas and the RPM's aren't high enough, the piston drops lower than it rides at idle. I'm seeing about 16 in/hg or more at idle, but the vac can drop below 5 in/hg at WOT from say 1500 RPM. I have to downshift when I floor it, or ease off the gas when the vacuum drops to 5. When going from cruise to WOT from about 2500 RPM it's similar, no popping but burbling starts to happen when the vacuum gets to about 10 which is still below vac at idle. Not sure about this, but I expect piston height is linear with vacuum regardless of load. If so, the pistons get close to the bottom. My modified N-27's worked better than the SM's in there now, only burbling a little going WOT from freeway speed cruise. Stock N-27's were not so good. You're right, the HF caliper is accurate enough for pallet racks, it's just irritating that they won't give the same measurement twice on the same metal, and you have to keep zeroing them. It would be OK if I was paid by the hour. Outside calipers are no good for them since you have to take a lot of inside measurements. Owners buy narrow ones with thin, non-seismic baseplates cheap and load them to the roof. All that measuring, testing and semi-rigid, non-linear frame analysis is total waste of time since the baseplates (tear-out at the anchor bolt holes) determine how much junk they can pile up there, but the building dept. wants to see it anyway. Besides, the Mitutoyo looks pretty cool.

Right, .0010 not .01. I bought two sets of N-27's from MSA last year. The needles weren't marked in ink or stamped, so I'm not sure. I got the pair of SM's for ZTherapy a few months ago, they had SM printed on the base. My '73 has 3-screws installed by previous owner; the needles in them were stamped N-58. '72 Nissan engine manual lists N-58 as emission spec for USA (and Canada?), N-54 as non-emission, standard elsewhere. N-27 stock for all earlier. MSA told me I needed early nozzles to go with the N-27's, something I don't understand. My measurement technique is pretty low-tech. The first run I held an architect scale against the needle, put my thumbnail at 1/8" points, and mic'd against the thumbnail. Second run (point to base) I stuck the needle through a strip of thick paper, moved the paper to 1/8" points on the scale, and mic'd against the paper. All without my glasses. I'm thinking about biting the bullet and getting a Mitutoyo. The HF is handy to have but I can't get the same reading twice with it, and need to zero it constantly. I may have a job coming up where I have to reverse-engineer a bunch of damn used pallet racks; last job like that I used the HF and it was a hassle to never get the same readings. So I guess I can justify the Mitutoyo for that. I'll be using a $120 instrument in a dusty, filthy environment, but I guess they're built to take it. Wondering if I should go dial or digital. Interesting that the SM's are way fatter (leaner) at the base than the N-27's. Maybe that's why it's popping or burbling if I stomp on it without downshifting. Information on the various Hitachi SU needles has to be available somewhere. Probably only in Japanese, but there's google and other translators. I read a post on an Australian Datsun site that someone took their nozzles to a machine shop and had them drilled to British spec just because they couldn't find that information. ZTherapy sells oversize nozzles, but that would make it way too rich at top end with the SM's, with stock displacement. I'm flowing more air though, so I need a slightly richer needle. So polishing seems like the best option.

Here's the average of the two measurements I recorded. The two I recorded were the same at stations 1,6,7, and 14. All the rest differed by 10 to 20. Here's the difference between my measurements and yours. +10 means I recorded .010" higher, etc. STA 1 2 3 4 5 6 7 8 9 10 11 12 13 14 +10 +5 0 +15 +15 -20 -20 +15 -15 -5 0 0 -15 -15 So no and yes.

Wish my carbs and linkage were that shiny. The hoses look OK, you might check the PCV hose at that sharp bend. It's hard to tell with the braid cover on it. To the left of the front carb, you see two hoses, the one from the vent of the float bowl lid, and the vacuum hose from the carb to the distributor. Between those two you can see a metal line with a hose attached to it. That metal line comes from the evaporation tank above the right rear wheel, and the rubber hose goes to the F.G.V. (flow guide valve) which is attached to the fender near the coil. There's also a hose from the air cleaner to the F.G.V. Air can flow from the air cleaner to the evap. tank if there's any vacuum. Gas fumes can flow from the evap tank to the F.G.V. and from there to the crankcase. But air can't go from the crankcase to the F.G.V. and out either of the other two hoses. If it does, the valve is shot and there's a vacuum leak. I don't know how to use a vacuum gauge to find a leak, but it's handy to have, especially with SU carbs. I hooked mine to that middle hole on top of the balance tube. Maybe I can find the photo.

So you checked the plugs and they're all still clean? I suggest putting in a new PCV valve if you haven't done that already. It's about $3 I think. You can easily test it without any tools but I forget the details. It's in the FSM I think. Check PCV hose, Brake booster hose, and all other hoses and connections attached to the balance tube. PCV hoses go bad from the heat of the exhaust manifold; if it looks crappy suggest ordering a new one if it's leaking or not. But I think you'd easily hear whooshing when it's idling from any vacuum leak big enough to cause the problem. Sometimes you need to wiggle a hose to hear it whooshing. When my brake booster got a leak I needed to step real hard on the brake to stop the car, and there was a whooshing sound when applying the brakes. The big metal tube on the front of the block, that the PCV hose connects to, has a connection for another little rubber tube that goes to the flow guide valve. If that system (except it's hose to the air cleaner which doesn't matter) isn't connected, might be a vacuum leak. See FSM for details and testing procedure. Possibly a gunked-up flow guide valve could stick open (mine was stuck closed until I cleaned it) and cause a vacuum leak, not sure about that though. You could put a rubber cap on that connection temporarily, to rule that out.

Sounds like a big vacuum leak or a fouled plug. If there was a vac leak big enough to cause that, you would be able to hear it by listening to the engine while the car is idling, unless it's a bad or clogged PCV valve. Maybe you checked that already. Cars don't lug (run under load in at too low rpm) very well with a fouled plug. If you slow down for a bump without downshifting the rpm drops, and if you have a fouled plug it would shake. When you bring the revs up it runs better. This happened to me recently. I cleaned the plugs (and leaned the rear carb) and that fixed it instantly. Plugs can foul fast, in a day or two. Fortunately we have old cars so it's very easy to check and clean the plugs, unlike some new cars that require a wheel to be removed. I use a small wire brush, I get them in packs of three at O'Reilly for a couple dollars. Also some carb cleaner, good rubber gloves with big cuffs, safety glasses, and a disposable P-95 mask. I have a small ratcheting torque wrench set for spark plug torque per FSM, with a socket and extender. I pull one plug at a time, blast it with carb cleaner, give the tip and electrode a good brushing, blast it again, wipe the threads, and reinstall. Takes about 10 to 15 minutes to clean all the plugs if you're not in a hurry. If it's not vacuum leak or fouled plug, or misplaced plug wires, that's good information, then you can rule that out and check other things.

After a couple hours on google search, I'm guessing there's no such thing as official measurements for the stations on the stock needles (N-27's, etc.). British SU's sure, but not Hitachi's. Maybe it's a secret. The same question was asked here in 2008 and no good answer. So has anyone (with a good eye, steady hand, and a good micrometer) measured and charted the stock needles? I've got some stock N-27's, modded N-27's, and some well-worn N-58's (I think), and well as the current SM's (data on those since they're British) and need to do some more polishing, but as I'm a novice at this, I would like to know where they started at, in case I want to buy or make some different ones. I spent (wasted) a couple more hours today measuring and tabulating (top to bottom, and bottom to top, as a check) stations on the stock and modified N-27's, but my ten dollar Harbor Freight digital micrometer and maybe my measuring technique wasn't up to it. Won't post the results in case someone think it's correct. Typically off by about 2/100th's of an inch, maybe more. Had to zero it after almost every measurement. Looks like the measurements need to be within about 1/100th to correlate with the printed specs (for British SU's) and document any modifications. According to the SU book, 5 seconds of finger pressure on the needle (in a drill press) with 200 grit takes off about .01", and the two needles should match within .01" at any station, so ... Other option is to wing it, grind away and not worry about mistakes.

Back in the 70's Car & Driver tested the 240z and reported 124 mph with the 4-speed. Considering C&D's usual attitude, I tend to believe them. If the car was stock height with stock pipes, modification in those areas would provide some more top speed. But that was a new car with a fresh engine.

I've creamed a lot of cars in my STI. In NFS Pro Street though, not the real.

Tuning the SU's is not that bad. The various methods all work if you do it right. If you download the FSM, or Blue's method, or the one from the other link, print it out so it's sitting on the fender while you do it first time. Need the uni-sen or synchrometer. It's almost fun. Just setting both at 2 1/2 turns down only works if the engine's perfectly stock, float bowl settings are perfect, your temperature and altitude are happen to be correct for that setting, and you're lucky. Even if 2 1/2 turns is correct for both carbs, you still need to balance them.

You're ready for summer.