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SF Bay Area, CA
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1985 Datsun 720
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xsdg's Achievements
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Do you have a timing light? That'll make it pretty clear if you're getting advance or not. Also, if you have access to a vacuum gauge, what's it reading at idle? Ideally, you want to read around 20 in-Hg of vacuum at idle. If you can take a picture of the engine bay, that'll help us figure out what exactly is on the truck, and consequently what might be going wrong. There are a bunch of different varieties of these beasts.
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It's weird. The answer is "sometimes."
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dm: for the feedback trucks, if there's a vacuum leak, they'll add fuel to get the AFR right. So now you're idling with extra air and extra fuel == higher idle.
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I believe this is indicative of a vacuum leak at the shaft that connects the throttle linkage to the butterfly. I had this on my feedback carb as well, and I didn't find it until I took it to a Datsun specialty shop; they smoked it and it was apparently clear as day. In my case, I disassembled the bottom section of the carb and found some O-rings that fit snugly around the throttle shaft, and inside of the little counterbore that's at the linkage side of the throttle shaft bore. Super hacky solution, but it worked. It's lasted me 2.5 years, but is showing signs that it needs some attention again. A more permanent solution might be to find a brass washer or two that fits snugly in the same spot — between the throttle shaft and the throttle shaft bore's counterbore. Maybe couple that with the O-ring. The legitimate solution is to have the carburetor re-bushed — there's a brass bushing in that bore that wears out over time, and that wear is what causes the vacuum leak.
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Good stuff! Just wanted to say hi. I have an '85 cali truck that I fixed up to the point where it'll pass smog, so if you have questions, lemme know. I think one fundamental thing to check is whether it idles at the right RPM. If not, that's often indicative of vacuum leaks, and hunting down vacuum leaks is a process. It's doable, but it'll take you some time. The smog place isn't supposed to pass a vehicle that isn't idling in the right RPM range, but sometimes they'll let it slide, depending. My truck came with oil leaks. I replaced the valve cover gasket and the oil pressure sensor (positioned aft of the oil filter, below the intake manifold) and that fixed it up, near as I can tell.
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Probably not directly related to your current problems, but I see that your float bowl vent line is capped off. That's probably not ideal, since it doesn't allow the pressure in the float bowl to equalize with atmospheric very easily.
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You're in CA with an '85, so I'm guessing you have a feedback carb? (Six wires, exhaust manifold has O2 sensor, etc.) Consistently high idle is generally indicative of vacuum leaks in a feedback setup. That's the first thing I'd hunt for on that problem. Second, 2.4V at choke is not right. Should be 12. And 2.4 is probably not enough to actuate the idle cut solenoid, which would _also_ explain why it wants to die once the idle drops — with the idle screw cranked in, the primary is open and feeding fuel. With the idle screw backed out the right amount, you should still be getting fuel from the idle circuit. The idle circuit fuel source will be cut off if the idle cut solenoid isn't powered. Easy check for now: run a jumper wire from the battery hot terminal to the idle cut solenoid. You should be able to hear it click when you power it. When you do that, try to avoid backfeeding the 12V into the harness from that point — could damage the ECU, depending on what other problems exist in the truck, and you don't want to be hunting for another one.
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Good luck with your surgery
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I believe (could be wrong) that the only requirement for the coolant overflow tank has to do with the relative level of coolant in the tank and the height of the top of the radiator. Also, make sure it doesn't run dry and suck in air :o)
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Spiff: is that 1100kg wet? What year? I took my '85 (cali Z24) to a weigh station and it's 2750lbs with fuel, without driver. So that's 1250kg without driver. I have a spare and an aluminum toolbox. Also, to Wayno's point, I did my couple-days-after-install pressure check and discovered that I had been misreading my inflation gauge — the last line isn't 0. So it had around 10psi per side in it. When I dropped that to 5psi (the recommended minimum), the ride improved pretty dramatically, so I'm basically completely happy with the setup now.
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720inOlyWa: I think it depends on how much time you're going to spend carrying stuff versus not. I generally drive around unloaded, so the air bags were the obvious choice. If I were carrying loads most days, I probably would have done something with the leaf springs themselves (whether replace them, or add a helper leaf). That option would be less adjustable, but more consistent.
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I had meant to say: one downside is that even with the system at min pressure (5 PSI), there's still a pretty significant increase in spring rate over stock. This is noticeable just driving around — it feels like the truck is slightly over-sprung in the rear, although part of that feeling might be the juxtaposition with the front, which is underdamped currently. Also, the unloaded ride height has increased, which means that roll center is higher. One result is that the truck seems to "fall over" in turns, whereas beforehand, it had plenty of body roll, but the roll was fairly progressive. Because of the camber gain in front when the suspension compresses, it means that I have to watch out for surprise oversteer now, which is a trait that the truck didn't have previously. Hopefully getting some stiffer dampers in the front will help to make the body roll more progressive again. All in all, I'll probably get used to the new handling characteristics (and as mentioned, I have some ideas on how to make things a bit better then they are currently). I'm still happy, because this means I can carry weight (including towing trailer tongue weight) that's cantilevered past the rear axle without losing as much weight off the front axle, so I'll still be able to steer and brake. You never realize how nice turning authority is until it goes away :o)
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BTW, I'm down in Santa Clara. I get up to the city every now and again, so if you end up with a Z24, I might be able to drop by to offer suggestions or lend a hand. I'm running the stock Hitachi carb and got my truck to legit pass smog with flying colors, even though it was trying to stall at every stop light back when I first bought it. I know next to nothing about the L-series engines or the diesels, though.
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Go Go Gadget air helper springs!!! The assembled air spring assemblies, in installed orientation. Red air fittings point towards the rear of the vehicle. Lower bracket installed. Front of the vehicle is toward the right. One of the things I like about this kit is that you keep the bump stops. All of the components (and tools) to mount the lower bracket on one side. Getting things lined up to install the upper bracket. Magically delicious! Drill 5/16" hole, then install 3/8" self-tapping screw. Thank goodness for impact wrenches Fully installed with air lines routed but not yet fixed in place. 0 PSI 60 PSI. Note that the jack stands are supporting the axle and not the frame, so the air springs (plus leaf springs) are supporting the full rear axle payload. This basically shows the unloaded vehicle ride height at 60 PSI. System max is 100 PSI.
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Bump! 720 stock ride height? I'm planning on doing this install today, after I run and get some food.