Captain Obvious

I just couldn't bring myself to take my car out in that rain. I hid at home in the dry garage instead. I really wanted to take a good look at some of those second or third revision Miata seats that your bud had for sale there. I've considered putting a pair of those in the Z. I've got Fiero seats in there now and I find them extremely comfortable, but I've always wondered how Miata seats would do. Couldn't stand the weather.

Yeah, I'm unfortunately in the same boat. If it was going to be a little rain, or just a chance of rain for a short period of time, that would be different. But the current forecast looks pretty wet, and I don't want to subject my not rusty Z to all that water. I guess I'll keep tabs on the details, but at this point, it looks like I'm probably going to pass.

Not trying to take business away from anybody, but an ignition switch isn't something I would buy used. Datsun didn't use a relay to handle the current for the starter solenoid and this is what happens inside:

I believe there are options available for a replacement thermostatic valve, but it won't be a direct drop in. There are valves for other applications (not necessarily specifically automotive) out there if you want the function and are willing to deal with having to modify the system to adapt a different form factor. Here's a couple ideas: Heat activated trap http://www.thermomegatech.com/product/hat/ Hot water balancing valve: http://www.thermomegatech.com/product-categories/domestic-hot-water-balancing/ There has also been some past discussion at the Z car forums. Here, Zcar, and Hybrid. Search isn't the best at any of them, but if you've got the time...

I took a look through the pics I've taken in the past, and everything is micro instead of macro. In other words, I've got close-up pics or wiring harnesses and ignition coils, but nothing of the show field. I'm guessing maybe twenty first gens?

Great results. Glad you could come up with a solution to your issues. I wouldn't necessarily call the water flowing through the carbs a bad idea though. It speeds warm-up and improves performance in areas of the world that are not as hot as where you are. It also prevents icing which could occur even where you are. It's just clear that "too much of a good thing" can cause problems. If your valve isn't closing until 195-200, then that's too high. Test procedure on 74 FSM page ET-5 says is should be closing around 130F. In your climate, I suspect 130F occurs about thirty seconds after leaving your house. Point is, blocking it off completely isn't much of a change where you live!

There was already a thread started about it couple days ago: http://www.classiczcars.com/topic/55453-0064/

It got a bid at 50K, and get this.... Reserve not met!!! He's got a reserve on it ABOVE 50K. It's beautiful, and I'd love to have it. But for that money? "All original?" In addition to what is in the ad and what has been mentioned above already: H4 headlights. Hood misaligned and standing proud at the front. Front tip of the hood looks rounded like it was pushed in and subsequently fixed. Crack in the right sugar scoop. Green paint overspray on the muffler? Speakers in the doors. Some weird mount (cell phone?) attached to dash. Poor fitting seat covers. Parking brake boot missing. Overspray on front strut tower nuts. Green overspray on floor pans under car. And what's the red spot poking out from underneath the VIN tag? That to me looks like the car used to be orange, but I don't see any signs of that anywhere else. Like I said, it's beautiful, and I hope for all our sakes he gets what he's asking, but geez!! And for that low of a VIN, I'd want history and mileage documentation.

I'm planning to attend. Been there the past few years. A little further for you than for me. If you do decide to go, get in touch beforehand so we can be sure to find each other at the show.

Excellent. So make sure you keep us posted on the original problem and what the behavior is after you figure out what you're going to do about that thermostatic valve. This would be the first well documented case I've been close to.

Sounds like I've brought out the inner Bubba in a bunch of you guys? I'm just going to cover my ears and pretend I don't hear any of this!

So something else you mentioned before... You said that the water passage going to the balance tube was clogged. That passage to the balance tube is primarily to cool the EGR valve and the balance tube where the EGR mounts. If your EGR system is functional, it get's extra hot there and I've seen reports of the passageways burning through due to the heat. Point is... If your EGR is working, you might want to make sure that line flows. Also, it's a good idea to keep some small amount of coolant flow into the thermostat housing, even when the engine is cool. Thoughts being, you don't want a stagnant pool over by the thermostat. In the stock configuration, you've got three ways for water to flow through the intake tract: 1) through the carbs, 2) through the balance tube, 3) through the intake manifolds. I don't remember if all of those three paths are regulated by the thermostatic valve, but if you do block off that valve, it might be a good idea to make sure at least on of those three paths still passes water somehow.

Excellent. Sounds like my skepticism was unfounded and I hope that you have identified the root cause. There has been chatter about that thermostatic valve in the past, but I'm not aware of a cheap viable alternative. I hope yours cleans up with the dunking, and if not, it sounds like you're going to have to just remove the carb water flow like so many 260 owners before you. Wow... Down to the 60's. Everyone wearing winter coats?

Haha! There is much disdain in machinist circles for those who use their drill press as an arbor press. Similar to the amount reserved for the people who use their calipers as adjustable wrenches.

The antenna trim screw probably adjusts the value of a small variable inductor of capacitor. I'm not sure if I'm understanding your findings or not, but there should be no visible physical mechanical change as you rotate the screw. The other problem sounds simply like a broken connection. Is it something that you can't just resolder into place? Can you take some pics of the area of concern? And as for off the shelf or not... Even if it was off the shelf in 1970, it's not off the shelf anymore. Things have changed.

That would be a fifteen second job on my hydraulic press. Thirty seconds if I had to adjust my table position for the length of the shaft first. Nyeah, nyeah!

Haha! Getting confident is just an invitation to let Murphy refresh you on his laws. And the cockier you get, the more expensive he gets. Patcon, It's still gets "cold" sometimes in FL. Heck... I could say the same thing about where you are compared to PA.

I like it! DId you make that up? "Anchoritis" kinda flows too.

Interesting findings and I hope it's that simple, but call me skeptical. Wouldn't be the first time someone thought they had a problem licked only for it to return again in the future. To test your theory, get the car back to stock. Fuel rail back where it belongs, water passages as they were a couple days ago, etc. And then recreate your shake test. Shake the car as you did before at hot idle, and verify that fuel glurps out of the bowl vent tube like it did before. Has to be repeatable. Then once you are positive that you have the car in the state where the fuel overflow will occur, shut the motor off, give it ten seconds or so for pressures in the fuel lines to stabilize and then repeat the shake test. If the theory about flash boiling the fuel by contact with the coolant passage inside the carb is correct, you will get a glurp of fuel out the vent tube even with the engine not running. But if you do NOT get a glurp with the engine off, then you're chasing a red herring. Reason being, if the overflow is caused by flash boiling fuel that is coming in contact with that internal heated passage, it shouldn't matter whether the car is running or not. Ten seconds after you shut off the engine, that passage is still at the same temperature, and the fuel level in the bowl is still at the same level. Results shouldn't matter whether the engine is running or not. Does that make sense?

Note that I've not actually tried that "inflate the bag" test technique. I was just thinking that if the float chamber is getting supplied with an overabundance of vapor, then that vapor needs to go somewhere. My first thought was trying to inflate a balloon, but I don't know how much pressure it takes to blow up a balloon. So I figured that a completely deflated plastic bag applied to the vent would require less pressure to inflate than a balloon. In fact, I would guess that a plastic baggie would take darn near zero pressure to inflate until it was plump. But by then, you'd already have your answer. I'm interested in getting to the root of the problems you're having because the reports of heat related fuel problems with the flat top carbs run far and wide, but I've never been convinced that it's actually a carb problem. I've never personally had any heat related issues with the flat tops, and this is the first instance where "replace" is second choice behind "fix". Most people just give up and replace.

Thought of another way to potentially test for pressurization of the float chamber. Maybe you could put a piece of tubing over that vent tube outlet and attach a deflated plastic bag to it? With the car hot enough to be potentially causing the problem, but sitting still, the bag should NOT inflate. But if the bag inflates, then it's an indication that you have gas (vapor, not gasoline) trying to escape from the float chamber. Normally, you have fuel flowing into the carb, and fuel flowing out of the carb, and the whole thing should be in pretty much equilibrium. But what I'm thinking might be going on is that you are not in equilibrium. You might have excess vapor that is trying to escape. Baggie over the vent tube outlet would probably be quicker and easier than clear fuel line? Fire extinguisher handy at all times!!

I'm not thinking that shaking the car exacerbates the boiling. I'm theorizing that the boiling (bubbling, emulsifying, however you want to describe it) is occurring all the time, whether you are shaking the car or not. Theory is that those bubbles are passing into your carb bowl and positively pressurizing the air pocket above the fuel level. When the car isn't shaking around, that vapor passes harmlessly out the bowl vent, but when you shake the car and get the fuel in the bowl sloshing around, you can temporarily close off that bowl vent hole. And when that happens, the positive pressure sends a little glurp of fuel up and out of the vent. In other words... The boiling isn't changing. The blockage is. When the car is sitting still, the vent hole is not blocked. But when the fuel is sloshing around, you are intermittently blocking that hole with a wave of fuel. I also suspect that if you're seeing fuel coming out of that vent hole, then I'd be pretty sure that you're getting fuel pulled out of that "axillary nozzle for starting" (your choke enrichment jet) as well. Might not be as visible as fuel coming out of the vent hole, but that nozzle pulls from the same source and it requires much less vertical lift than that vent hole. if it's coming out of one, I bet it's coming out of both. As for you not hearing bubbles back at that tank, the theory is that the front carb swallows most of the bubbles, the rear carb gets most of the remainder, and tank return gets very little? Maybe that's why you don't hear bubbles back at the tank? And as for the thermostat I was talking about. There's supposed to be a small thermostat in series with the carb coolant lines. It lives back by the bulkhead wall near the rear of the block. Where the coolant lines turn the corner towards the passenger side of the head. On page EC-2 of the 74 manual, they call it the Water Control Valve" and it's a temperature control valve. Most of them are clogged (or removed) by now. I'll see if I can dig up some more info about it.

So sitting still with the engine hot and idling, you can rock the car back and forth enough such that fuel glurps out the bowl vent tube? Wow. In this pic, you can see the round sight glass hole in the side wall on the left, and the oval shaped hole in the lower right side is where that vent tube connects. If the bowl level is correct, you need about an inch and a half of vertical lift to get fuel to spill out that vent tube into the carb throat: Just another view of the same. In this pic, the sight glass hole in on the top, and the vent location is at the bottom: Makes me wonder if you might be vaporizing the fuel in the fuel lines and not having a problem inside the carb itself. It's been a long time since I've seen 260 fuel rails, especially without the heat protective wrap, but if memory serves correct, the front carb pulls off the fuel rail first, and then the rear carb, and then the remaining excess fuel is routed to the pressure regulator orifice. Grasping at staws, here's a theory... You aren't boiling the fuel in the bowl, but are vaporizing the fuel in the lines somewhere, and blowing big disruptive bubbles of gas vapor into your float chambers. And those big disruptive vapor bubbles blowing into your bowls need to escape from the float chamber. If liquid is sloshed even a little bit up into the bottom of the oval vent hole in the roof of the float chamber, the positive pressure in the chamber pushes liquid up and out of the vent tube. And thinking that maybe if the front carb pulls off the rail first, theory might be supported by the symptom that the front carb does this more easily than the rear? Cavitation at one of the pumps maybe combined with high temps causing big vapor bubbles in your supply lines to the carbs? Low pump inlet pressure caused by a supply restriction? Positive displacement mechanical pump up at the engine doesn't like the style of electric pump being used to supply it? Can't deal with the pulsed nature of the demand? To test for this, you could temporarily replace the black rubber fuel lines feeding the carbs with a clear piece of vinyl tubing. That way you can get a view of the fuel supply as it leads into the carbs to see if it's solid or all full of bubbles? If you're squeamish about generic vinyl, there is fuel rated Tygon (usually yellow), but for a temporary test, I think the generic clear stuff from one of the big box stores would be fine. And fire extinguisher handy at all times!! Some additional questions while I'm here... So all the coolant lines are connected. There's supposed to be a thermostat in series with the line that leads through the carbs. Do you know if that thermostat is present, and haha... working? I know, I know... What type of electric pump are you running? And is it in the stock location in back? The stock electric pump would allow for passive pull through, but depending on the internal design, some electrics won't. And lastly... You've got a catalytic convertor? Is your car originally from California, or is it something that you put on? I don't think that a clogged cat would cause the problem, but it certainly wouldn't help keep the temps down.

Haha! I see what you did there.

Yeah, I'm very happy with the way this project turned out. It's a lot easier of a project if you're willing to use the donut spare "as-is" and accept the hassle of dealing with switching two tires in the event of a front tire blowout. The offset of the original donut wheel is very wrong, but again... Emergencies only. Dennis, I'm not sure why you would bother with a mini-spare on your 71. I'd love to run a full sized "regular" tire back there, and the only reason I went through all this work was because I can't due to the reduced tire well diameter on the 77/78's. If I could have run a normal tire, I would have never taken on this project. Why are you wishing for a mini-spare?