Zed Head

You're right, it's not completely gone. It starts kicking in at about 3-6 inches of vacuum and gets full at about 11 or 12 depending on the distributor, by FSM numbers. Back to WN, it's funny that someone who hasn't checked that their timing works right is calling someone else an idiot for putting an inline valve in backward. Just sayin', maybe the frustration is misdirected. :devious: I like to pick on people who call names... p.s. Interesting side-note - my 76 280Z didn't even use the vacuum advance unless the car was in 4th gear. It actually has a solenoid valve on the vacuum line, activated by a switch in the transmission. Weird.

What brand/kind of tires did you get? Maybe the old cracked ones were of higher initial quality. If the rims with old tires were balanced, then the new problem might have come with the new tires.

Under heavy load, with the throttle open, the vacuum advance goes away. Vacuum advance comes in to play at partial throttle openings when the intake vacuum is high enough to pull on the diaphragm. You'll feel more "pep" at a partial throttle but probably not much when climbing hills or accelerating quickly. Check your mechanical/centrifugal advance mechanism. Easiest is with a timing light and the vacuum advance hose disconnected.

I need to learn how to use them emoticons. A lot of good information here anyway, as a result. I didn't know that the 260Zs were using EGR, it didn't show up on the Federal 280Zs until 77 or 78. I guess the EFI let Nissan back up a few years. Plus, the whole argument about not needing the switch if you don't need the extra distributor pickup becomes less relevant since the switch is used for EGR. No harm, no foul:beard:

I think that you're mistaking my quest for clarity and knowledge with a challenge to what you're saying. It's not. It's exactly what I wrote and the picture I posted. mousemedic said "only", I showed why he might have said that. Now, you have shown, with your references, that there's more to the story. This is the internet. The best way to get someone to believe the point you're making is with examples and references. Without those, how do you know if anyone really knows what they're talking about? And how do you explain it to someone else? "A guy from the internet said it was so". Thanks for the link to the EC section. Now we're learning.

Just trying to help people get on the same page. In this case, page EE-27 of the 1974 FSM.

It's hard to figure out what exactly you're describing. I don't even see the "wire in question" in your first post. You can test the headlight switch directly by taking the plastic cover off of the top of the steering column and measuring voltage in and voltage out at the switch. The wires and their soldered attachment points will be exposed with the plastic cover removed. Measure from the power input wire to ground, see if you have battery voltage. Turn the headlights on and measure the output wire, you should see battery voltage. If you have both of those, then move over to the dimmer switch on the turn signal stalk. That is the ground for the headlights, one for low and one for high. It's common for the dimmer switch to get gummed up and not provide a good ground for the high and low circuits, either one or or both. You can spray contact cleaner in the dimmer switch and work it back and forth sometimes, to get the headlights working.

mousemedic might be going off of what is said in the 1974 FSM. Kudos to him for checking the factory source. It says that the automatic only used the water temp. switch to switch pickups in the distributor. Of course, 1974 is the year of change so it wouldn't be a surprise if the manuals had the switch also, like the 280Zs do (auto and manual), or they added it to the manuals when they went to the big bumpers. To correct one thing in mm's post though, the timing is advanced when cold, then goes back to retarded when warm. My guess is it's another idle speed increaser, like the AAR. It's described n Engine Fuel, not Emissions. It seems like a lot of technology for an unexplained effect.

Pretty sure that's not the proportioning valve. It's only purpose is to show a failing brake system, by pressure differential between front and back. The proportioning valve is in a different location and does not have an electrical switch inside. You're right though, that is could be a source of brake light problems. I don't think it needs replacing if it's triggered though, it automatically re-centers itself when the pressure differential is fixed. The brake check warning lamp relay under the passenger seat could be involved in a brake light problem also.

You might be able to break the seal by knocking it on the side with dead blow or rubber mallet. It would help break up the rusted bolts also. Tapping back and forth would let any PB Blaster, etc. works its way in to the bolt holes. As Walter said, a drill will probably walk on off the bolt end and in to the aluminum housing. You might also put the thermostat cover back on the top and use it as a lever. I've had one that I drilled and removed but ended up with the through hole enlarged, and another that I was able to knock loose and work back and forth to get free. The rust from the bolts fills up the through hole in the aluminum but will come out as powder if you can get it moving.

I saw in your previous post that you've put a new exhaust system on. They will look under the car with a mirror for a catalytic converter if the door tag says it's supposed to have one. Just a heads-up for you. As far as the idle emissions spec. you'll get multiple tries to get it right. No fees until you pass.

Engine RPM is mainly controlled by air supply. Which is mainly controlled by the throttle body. The AAR bypasses the throttle body when it's open, that's why it was a good place to look. Leaking hoses can let air in that will increase RPM, as long as there is fuel available, so any hose attached to the intake system should be checked. The PCV system can let air in from the crankcase, if there is air leaking in to the crankcase. For example, through the dipstick tube, valve cover gasket or oil fill hole. Can you get the idle to hang high while watching the engine with the hood open? A weak throttle return spring or sticky throttle blade can hold the idle up. That sounds more like your problem since the idle eventually drops down. Watch the throttle blade lever and see if it's dropping back to its stop quickly. The AFM just responds to the air flowing through the throttle body, so it's unlikely that it would cause a high idle.

We're in to the minutiae now. My main point was the old adage "don't believe everything you read." You could also add "make sure you understand what you're reading." Racer Brown's article can be interpreted in many different ways. I don't see anything in it that can be used to decide if the #3, #2 or #1 hole is "better" for a new chain and sprockets, on a stock engine. Cam timing retardation happens, but retardation from what starting point - "optimum" (subjective, and maybe Nissan missed the retardation effect) or already advanced (because Nissan engineers are no dummies)? After siteunseen has it done and reports back, we can discuss the relevance of "butt-dyno" results,and what oomph means. Site, maybe you could do some 0-60 runs to give some measurable results? And thanks for the opportunity to hash out some new topics on your thread. Good luck with it. By the way, it seems that Nissan gave up on the three adjustment hole idea in the later ZX L28s. It's not mentioned in the FSMs anymore. Probably caused too much time-wasting internal discussion among the engineers.

Use a punch to drive them through and out. It's a tapered pin, no threads on the inside only on the end where the nut was.

I guess we all get something different out of the same words. I actually left out the words that got me going, they are below. Racer Brown is suggesting that the original design is wrong, or that the Nissan engineers missed something. Statements like that just get me wondering how the writer came to conclusion, and in this specific case, it looks like a guess. Cam timing is one of those things that's hard to mess with, without risking damage, and hard to measure results without a dynamometer. Even measured, you have to know what you want before you can say it's better or worse. Do you want oomph or high RPM HP? It's all good conversation, didn't mean to offend with my engineer comments. Scientists are even worse. Here are the statements that offended me - "Datsun chains are quite long, about 42 inches in circumference, with 110 links, which means that keeping the valve timing exactly right at all times, is nearly impossible. It is therefore better to start out with a slightly advance camshaft - say by 3 or 4 crankshaft degrees - because there is no way in the world that it can be kept from retarding itself as the engine is run, particularly at high engine speeds. This is also the reason for the three different timing marks and three different dowel pin holes in the Datsun camshaft sprocket; they make provision for advancing the camshaft in 4-crankshaft degree increments, but they make no provision for retarding the camshaft. It does that by itself with no outside help required!"

Here's one. His writing implies that the three holes are for power band adjustment, if you're going to run at high RPM. If you want to, they are there for your pleasure. Don't worrying about retarding the cam timing, it's self-adjusting!! Just rev it up higher until the cam timing is where you want it! "because there is no way in the world that it can be kept from retarding itself as the engine is run, particularly at high engine speeds. This is also the reason for the three different timing marks and three different dowel pin holes in the Datsun camshaft sprocket; they make provision for advancing the camshaft in 4-crankshaft degree increments, but they make no provision for retarding the camshaft. It does that by itself with no outside help required!" Another obvious follow-through on this discussion is that retarding your cam by installing it off one tooth and using the holes to dial it in, still retarded, will give more high RPM power. Move the power band higher. Maybe the racers are already doing it, it's easy, and cheap. A little porting work to let the engine breathe, slip the cam chain a tooth, and you're making cheap, easy HP.

His words (Racer Brown's) imply that he knows what the Nissan engineers were thinking and why they had two adjustment holes. He doesn't offer any evidence for retarded cam timing, using a good condition chain and sprockets though. He just offers an idea of why they might be there. The FSM explains in clear times what they're for - adjustments for wear. For the record, I have worked with many engineers and know that passing courses and getting an engineering degree is no guarantee of logical, clear thinking. To the contrary, I have met many engineers who assumed that because they were engineers, that their thoughts, on any and every thing, must be correct. "I have an engineering degree, I must be right." As I said, great for conversation, but don't spend your money on what's said until you see the evidence that it's true.

No offense Leon, I didn't even notice who posted the thread. I've read the article before and wondered then where this guy got his ideas from and decided at the time that it was mostly theorizing. My point was to take it with a grain or two of salt. It's good for understanding what might happen, but short on showing what really does happen. Great seed material for more discussion.

The Racer Brown article is full of conjecture and guesses. A great place to start for experiments and good ideas to be aware of, but there's no facts to back up the claims. It looks like someone just writing down their ideas of what "must be" happening. The two extra holes are most likely there for chain wear as the FSM describes.

The clues do seem to point to exhaust. Seems like a good muffler shop would know what a clogged exhaust system sounds like. The gases don't pulse the same coming out of the pipe. Might be worth having one take a look. Find an honest shop, of course. The lack of vacuum advance could be due to the lack of intake vacuum, which could be related to a clogged exhaust system.

Could be the BCDD. It's purpose is to cut fuel flow and reduce intake vacuum, through a throttle blade bypass channel, above 2800 RPM and 10 mph, under throttle closed deceleration. It's mounted under the throttle body and has a power wire connected. It's the weird looking thing with the rubber boot on it. It's an emissions device so is described in the Emissions section of the FSM.

Kind of stating the obvious aren't you? Experiments that yield measurable results are part of the method. So if someone (the mechanic in this case) has advanced the cam to #3 and felt more "oomph" then they've applied the method, and have knowledge. The discussion can revolve around what oomph means, but if your mechanic has done it and knows what happens, then you can only go off how well you trust him. If he was my mechanic, I'd ask him what he means by "oomph" and what I might lose by doing it - peak HP, for example, if what's described above is correct. If he's just working off internet rumors then you and your engine become the experiment.

Pretty sure that I've seen similar referred to by one of those guys who seems to know a lot, on another forum. One of those old tricks. It's interesting though that people will spend lots of time and money to get their cam set perfectly to the cam builder's specs., using a degree wheel and adjustable timing gear, but will throw an extra 8 degrees of cam advance in for more "oomph". Just an observation about engine tuning. Lots of mystery there, when it comes to cams. If you search around Hybridz, you might find some threads. I think that Tony D had some stories about cam timing tricks. If you're in the waiting room tight now and the question is what to watch on the big screen, the Euro 2012 semi-final is on in about 1.5 hours. If you're in to that.

I know that a lack of timing advance will reduce power, but don't know how much is not enough. Personally, I like to know what the numbers are so I have measured both vacuum and centrifugal (mechanical, centripetal... refers to same thing even though maybe not the right word) on mine. If you have the timing light on and rev the engine up until the mark passes the end of the scale, you'll know you have at least 20. You can probably eyeball it up to 30. Kind of hard to tell since "bog" is a subjective word. One man's bog is another man's hesitation. Plugged exhaust still seems like a potential cause also.

I believe that he's saying that his bushings are too small, not too big. Removing the liner would make it worse. Maybe the bushings are designed like the mustache bar bushings and need a "liner" and IK's are gone.