Captain Obvious

I was thinking the same thing. I can't believe it actually ran on that stuff!! I ran my 260 for a little bit on the old stuff from the tank and it left this very sticky residue all over the insides of the carbs and intake manifolds. After five minutes of running, the throttle butterflies got sticky and would hang up just from the glue. Gross.

I think we're talking about different tubes. The 73-74 tubes I was referring to are screwed into the bottoms of the carbs, not the intake manifolds. The faces of the 73-74 carbs have these trapezoidal shaped holes for water passageways that they could have used to pass water through the spacer and into the carbs (like the 72's), but they didn't. They chose to plug those holes with rubber plugs and drill and tap new holes into the bottom of the carbs instead. Then they screwed metal nipples into the bottoms of the carbs for coolant inlet and outlet. Here's a plc with a good view of the coolant tubes and the faces of the flat tops: The holes I think you're talking about are on the intake manifolds - Four holes on the front one, and two on the rear? Four of those holes (the rearmost four threaded ones) are to mount the idle bypass tube for the 73-74 tubes. Note that one of yours has the twisted off remains of one of the idle tube retaining screws broken off stuck in the hole. Doesn't affect you, but that's what that is. The other two holes (at the front of the front manifold) with the vacuum nipples pressed in are for constant vacuum sources and were not used for distributor vacuum advance. Probably academic, but those vacuum holes were originally used for a) the throttle opener device, and 2) the anti-backfire valve. The vacuum advance should come off a ported source on the carb bodies, not the intake manifolds. Here's a crowded shot of a mostly stock 260. You can see the mounting screws for the idle screw, and the bundle of snakes of other vacuum lines, etc: As for what to do with the holes... I believe the holes for the idle tube are blind, and you can just leave them open. The other holes with the vacuum nipples, you'll have to do something with. I don't know how much emissions stuff you're planning to run, but you might need one of them for a throttle opener system? Other one just cap? Or get elegant and pull the tube out and weld the holes shut?

7tooZ, That system is beautiful! I hope it works as well as it looks!

Wow... On the short list of things I did not need to know today, I believe that's at the top.

Thanks for the pics. It's been so long since I've seen them from that angle that I didn't remember the details of the face shape or the holes. I can tell you with certainty however, that the phenolic spacer plates for 73 and 74 have the six sided shape like the ones from your 72. The differences are that the 72's have coolant holes and are thicker. With the flat top carbs of 73-74, they used thinner spacers. Presumably to account for increased girth of the flat top carbs and/or the accompanying air cleaner. The mounting faces of the 73-74 carbs have coolant holes on the mounting face, but they didn't use them. They drilled and tapped holes underneath for metal hose nipples instead. The whole thing with the carb heating seems like they kept changing it and never got it all worked out. Then in 75, they went to EFI. Also, unrelated to the above, but if you're interested in amassing info about the early carbs... I haven't researched it in depth, but believe the 70-71's were the four screw round tops, and the 72's were the three screws. Makes it easier to identify quickly from the top without having to see the shape of the mounting flange.

All of the carbs 70 through 74 use the same mounting bolt geometry. The holes are in the same location on all of them, meaning that any carb will bolt up to any manifold. They changed the thickness of the phenolic spacers at times (70-72 are thicker than 73-74), and hence, the stud length to compensate. But all of the holes and studs are a square pattern and are in the same locations. They changed the water routing scheme over the years as well: 70 and 71 used the square mounting face (pic of the carbs in the bag), and they did not route any water into the carbs. 72 used the six sided mounting face shape you have pictured above with the holes in the phenolic. They routed water through the holes and into the carbs. 73 and 74 also used the six sided mounting face, and were capable of routing water through the spacer and into the carbs, but they did not do that. Instead, they used a solid phenolic spacer without coolant holes and ran a complete additional independent coolant stream to the carbs. This coolant path is in addition to the one that ran through the intake manifolds. So about your statement here: The 260 intake manifolds (the N36's) used a square attachment points (as every year manifold did), but they had the six sided face. It's been too long and I don't remember if they put water holes in the N36 manifolds on the carb mounting faces. I know the phenolic spacers are solid, but I don't remember if they bothered to put the holes in the manifolds themselves. Have you got any pics of the carb mounting faces of the N36's with the spacer removed?

Ewwwwwwww!

I don't have the ZX manuals downloaded. Anyone know what is the unlabeled device between 8 and 6?

Not sure this adds anything to the discussion, but I once cut up a stock pulley/dampers on my lathe to reduce the number of pulleys. I was just messing around at the time, but if you were concerned with the accuracy (I wasn't), it wouldn't add a lot of time. Here's a pic: More pics and some details here: http://www.classiczcars.com/topic/50727-a-project-is-brewing/?page=2#comment-46928

Won't you take me to..... Welcome aboard!

Based on my understanding of the system, I believe you nailed it. Needing that vacuum line at the back of the car kinda negates some of the advantages of moving the can though, doesn't it?

Cool. Glad you got to the bottom of the issue. I second the call for an autopsy of the screwy throttle body. Send it to me if you don't want to do it yourself. I'll open that sucker up! Dave, I would expect the same thing. With the wire off, you might discern a longer time to return to idle if you blip the throttle. Probably not a lot longer, but you might notice some difference. While you were in there messing around, were you able to determine if there was any change in idle speed with the wire connected vs. disconnected?

Zed, I dont know how large the passageways involved are, but yes... If my understanding is correct, it could/should result in a small decrease in idle speed if you were to disconnect the wire at idle. And yes, it would just be baked into the idle screw position. JSM, good luck with the investigation!

I don't know about new new cars, but they used the same basic concept in the 2000's. Couple differences though. The cans weren't always round, but were shaped to fit whatever tiny odd shaped space was available, and another difference is that the actuation was usually electrical through the use of a solenoid valve instead of the vacuum driven valve built into the cap on top of the can. They used the control brain to purge the can under the desired conditions instead of a vacuum signal. And diagnostics were incorporated into the system as well.

Well moving the carbon canister to somewhere else ought to be no problem. I think getting rid of the tank behind that rear quarter panel would be a little more risk. You do not, under any circumstances, want to push liquid gasoline into your carbon canister. My read on that overflow tank behind the quarter panel is that it is the highest highest highest point that liquid could ever ever reach. And then they pull a line off higher than that for the vapor recovery system.

Zed, the BCDD operation, as I understand it, goes like this... Chamber #17 is a pneumatic amplifier. If there is enough vacuum in chamber #17, it will lift plunger #9 off it's seat and allow some vacuum into chamber #18. And then if there is enough vacuum in chamber #18, it will lift plunger #13 off it's seat and allow air to pass around the throttle butterfly. So some points of interest... The further run in the adjustment screw on the bottom, the easier it is to lift #9 off it's seat. That's why the BCDD will operate at a lower vacuum. When the solenoid is energized (and the pin is retracted) this defeats build up of vacuum in chamber #17. This is because vacuum pulled into chamber #17 from the intake manifold side is just bled off by pulling in air from the upstream side of the throttle body. In order to enable the BCDD, they block the bleed passage on the upstream side of #17 and allow the vacuum from the intake manifold to build up in chamber #17. If that vacuum gets high enough, it will lift the plunger off it's seat. Keep in mind that I didn't design the thing, but that's my read.

Disconnecting the wire will enable the BCDD (which is the wrong direction and not what you want). If you want to completely disable the BCDD, turn the adjustment screw (#6 above) counterclockwise (when looking at the screw head). In fact, you can take that screw completely out. If the diaphragms inside are intact, the BCDD should be disabled completely. Of course, if one or more of the diaphragms has a hole in it, there's no telling what that thing is gonna do. Could disable, or enable it. Also, if there is a goober of carbon gunk holding one of the BCDD valves open, then things get unpredictable as well. To test if your problem is the BCDD, you could probably take off the rubber boot on the front of the throttle body and put a small piece of tape over the BCDD holes. Put the boot back on and start the engine. I wouldn't rev the engine for fear of sucking the tape off and down into the engine, but as long as the throttle butterfly stays closed, you would be OK for just a test. We'll figure this out!

Sorry, but I'm not sure I'm understanding... You are correct that as long as it's plumbed the same as the stock can, then that Sentra can should work just fine. You need three connections to the carb can. A vapor IN connection, a vapor OUT connection, and a CONTROL signal connection. The vapor IN connects to the overflow/separator tank thingie inside the right rear quarter panel. The vapor OUT connects to any constant always present vacuum source like the intake manifold, or the balance tube (if you're running carbs). The CONTROL signal connects to the ported vacuum signal that is also used to control distributor vacuum advance (high vacuum just above idle and no vacuum at other throttle positions). If you've got those three connections to it, I don't think the physical location of the can matters. I was just questioning if you were planning to have access to that ported vacuum signal. I wasn't sure if you were planning to run the original throttle body, or switch to carbs that did not have that signal available.

Well then I'm not sure I understand your question when you asked "To remove the BCDD is simply plugging all the vac lines to it?" I thought you were asking if you could remove it from the system (disable it) by plugging the vac lines that go to it. Were you suggesting a way to disable it, or are you suggesting taking it completely off the bottom of the throttle body and replacing it with a solid block-off plate?

About the charcoal can... They use a ported vacuum source to actuate the canister purge. They don't want to pull air through the can at idle, or at WOT as it is essentially a controlled "vacuum leak" and could adversely affect stability at idle and performance at WOT. The only time they purge the can is at light cruise. So... With all the changes you're making, are you planning to still have access to a suitable ported vacuum source peaking at light cruise?

Well I did a little digging to try to refresh my memory on exactly where I removed metal to allow my parking brake handle to sit lower, and I still don't know. A little embarrassing. I took a couple pics of the assy on the car (with the parking brake removed), and it looks like I may have cut a new rack gear or two at the bottom of travel. Kinda hard to believe, because the teeth look perfect and I don't remember putting that much effort into it! If you want to wait, I've got a plan. This past summer, I bought a new rubber seal for the parking brake pivot ball under the car, and I'll take this off season opportunity to replace that seal. In order to put the new seal in, I'll pull the brake assy and take some pics. However, if you've got the ability and opportunity to lower yours by relocating the mounting bolt hole, then that should work great too!!

I don't know anything about 79, but for all the previous years, it's not a simple matter to disable the BCDD. 75-78 has one wire going to the BCDD, and that wire needs to have +12 on it to disable the BCDD. Meaning that if the wire is disconnected, the BCDD will be enabled. And as for vacuum connections... There are no externally accessible vacuum controls for the BCDD. There are two vacuum ports coming off the throttle body that LOOK like they might have something to do with the BCDD, but they do not. They are both ported vacuum sources that go to small holes in the throttle body bore to control distributor advance and EGR operation. Even though they look like they are for the BCDD, they are not. All the BCDD vacuum ports (both control signals and operation vents) are located internal to the throttle body casting and do not come out to the outside world at all. Like I said, I don't know 79's details, but if the BCDD is on the underside of the throttle body like 75-78, then I would assume it's pretty much the same.

Here's a sketch of what I did to the parking brake assy. Note that it's a hardened pawl on a hardened gear so a file will just skate. You can't do it with a simple file. I didn't trust myself with a grinder, so I used a small square profile diamond file. I'll see if I can get an actual pic of what I did, but in the meantime, this should describe it. So at the "new" bottom of travel it doesn't click because there aren't any teeth, but you can adjust the at rest position like this. After making this mod, it made the addition of my return spring (other thread) even more necessary:

I don't know what happened with the original pics, but here are some replacements. Top side: Bottom side: Close up:

Yeah, I agree. That's exactly why I went through the effort to move mine up there. I wanted to get rid of the rats nest of hoses under the dash and simplify everything under there. I figure the fewer separate hose lengths and fewer clamps, then the fewer leak sources. Only reason I would use to justify putting it under the dash is that I believe the Escort core and the newer plastic bodied ball valves to be more reliable than the old stuff. I think at this point, if I used a new style ball valve and figured out a way to stuff it under the dash, I don't think I'd ever have to mess with it again. It would become the new owners problem at some point hopefully long in the future.