Late 260Z Smog Pump adjusting arm

[tunesnxs]

I'm trying to install the smog pump on my all original Late 260Z (with A/C) and can't find where the adjusting arm attaches to the engine/front cover. Does anyone have any photos of the installation? I'm having crazy "vapor lock" problems and I believe if I can get the smog pump back on the engine, it will cool the engine bay just enough to stop the "vapor lock".

Just for info on the "vapor lock" problem, when the engine gets up to temp, it will "burp" gas out of the carb (usually the front, but sometimes both it the weather is very hot outside) (it runs like a champ in the winter) and while the engine is at driving speed I can usually keep it running by flooring the gas pedal to clear the gas out of the engine. If the car is idling at a light it will glurp the gas out the carb, and choke the engine out. I'll have to floor the gas petal for about 20-40 seconds to clear the flood out and restart the engine.

So, back to the smog pump. I think adding the cooler air into the exhaust  will help lower the under hood temp just enough to stop the "Vapor Lock". So if anyone has any info or photos on installing the smog pump adjusting arm I would be greatly appreciative!

....or if you know of the problem I'm speaking of and think I'm on the wrong track, then by all means please point me in the right direction.

[zKars]

The smog pump will have no effect on under hood temps. Don't bother.

Check your fuel system to ensure correct volume and pressure specs. Change the filter at least. Possibly also replace the needle and seat in the carb where you see the overflow. This is either excess pressure or a poor needle seal.

[motorman7]

Pump pics

[Captain Obvious]

I also think you're on the wrong track thinking the smog pump will fix the issues you're having. I don't know what's going on, but I sure don't think a smog pump will fix it.

In general, the problem you're describing here where raw gas bubbles (boils) in the bowl and spills up into the carb throat is called "percolation", not vapor lock. Just like a coffee maker... You boil the liquid in the bowl and it runs up a tube an spills over into another area of the device, Just like a old percolation style coffee maker.

So you're saying that it will actually vurp gas out of the carb mouth while the engine is running???

And this is a late 260Z... You running the original flat top carbs, or have you swapped them out for a set of round tops?

[tunesnxs]

Yes capt. obvious, it is a late (12-74) 260. It is my 3rd "260" and this one is my all original, so yes it has flat tops. It seems to be percolating out the "auxiliary nozzle for starting" (#6 on drawing ET064 260Z FSM). (I could be wrong on the location of the glurp, but that's where it "appears" to be happening.  When I feel the bottom of the carb, where the fuel bowl is, it does seem to be cooler than the rest of the carb, (as one would expect) so I agree it sounds unlikely to be boiling, but I really don't know what else it could be.

I have 4 sets of flat top, Hitachi carbs that I try to keep freshly rebuilt. Two of the sets are my favorite as they look and operate (on the bench) better than the other two sets. They have been rebuilt and swapped three times now.  (Twice before the engine rebuild, and swapped again with the engine rebuild). The problem only seems to get worse with time.  ...and temp!  If the outside temp is over 85°f the problem will begin. Over 90°f it becomes just to dangerous to drive. 

It does happen more when accelerating from a dead stand still, or when turning to the right. The right turn is the worse, but they are both very obvious. When you drive the car to warm it up, then remove the air filter cover and watch after driving it, you can see the gas pouring from the carburetor (mostly the front, but occasionally both) 

I have re-worked the fuel tank as it was full of rust and debris, and have regularly changed the fuel filter until they began to stay relatively clean, as it is currently. The electric fuel pump was replaced last year and appears to be operating correctly. Mechanical pump is mechanically pumping and all the fuel lines are clear with the return orifice clear and of correct diameter. 

I'm not really sure what else to try so, I'm really open for suggestions here! 

[tunesnxs]

29 minutes ago, tunesnxs said:

 When you drive the car to warm it up, then remove the air filter cover and watch after driving it, you can see the gas pouring from the carburetor (mostly the front, but occasionally both)

well..... not exactly pouring from the carbs. It "glurps" out, as if percolating, maybe once every minute to 5 minutes (when standing still at idle). When it glurps, it floods the engine and naturally the engine stalls.

[tunesnxs]

Update, ...the fuel is not coming from the "auxiliary tube" but from the (for lack of a better term) fuel bowl pressurization tube that faces out in the mouth of the venturi of the carb. See photo. As best I can tell, that tube (which is a hole open to the atmosphere, to the fuel bowl) 

As soon as the fuel in the bowl gets sloshed onto the wall of the fuel bowl, then it comes gushing out of that tube. 

The fuel seems to be at the correct level in the fuel bowl, as viewed by looking in the inspection window on the side of each carb. 

[motorman7]

Glad you are sticking with the flat tops.... I miss mine.  I sold my silver '73 240Z and am still kicking myself for doing that. Never had a problem with the carbs after I did the rebuild...even in traffic on the 5. 

[Captain Obvious]

That tube is simply a vent from the float chamber to atmosphere. And I know you already know this, but there's no way there should ever be fuel coming out of that vent tube.

So, you're positive that your fuel pressure is in spec? And you're double dog sure your float levels are correct?

With a good flashlight and a small inspection mirror, it is possible to see the sight glass levels even with the motor running. Have you confirmed that it isn't, in fact, a transient level issue?

If you're float level is correct and you're not intermittently overwhelming your needle valve with an overly high fuel pressure from your pump, then maybe you are in fact percolating the fuel in the bowl.

Do you have the original heat shields attached to the underside of the float bowls? When you say the bowls feel cooler than the rest of the carbs, are you feeling the bowl cover itself, or the heat shield that is (supposed to be) bolted to it. Are all other heat shielding entities still in place? Do you have the coolant tubes to the carbs hooked up, or have they been disabled?

I know it's hot there, and even hotter under your hood, but still...

[tunesnxs]

Capt. Obvious,

 

    Yes.... to all the above!

I agree there should be no way that fuel should be coming out of that tube. I ran the car at idle yesterday when I got home, and watched, and waited. Once the car got up to temp, all I had to do was jostle the car a bit (shaking from the fender to create an oscillation with the tire play), just enough for the fuel in the bowl to slosh a bit and >SPLOOSH< out comes the gas from that tube!! Of course with the engine running, a lot of that gas gets sucked into the carb, floods the engine, and it dies.

I'm not positive my fuel pressure is in spec, but I watched the fuel level in the bowl through the sight glass and other than the waves caused by the engine vibration, the fuel level stays right where it should! Even with hard acceleration the fuel level never goes above the middle of the sight glass, which is the best method I know to ensure the float levels are correct!

All the original heat shields are in the proper place. One isolating the exhaust manifold from the carbs. and both on the bottom of the carbs with all the asbestos still firmly attached. When I was feeling the bowl, I was in fact feeling the bowl (between the heat shield on the bottom of the carb, and the bottom of the carb) It was not too hot to touch, unlike EVERYTHING around it!!!! (ouch, ouch.... ouch.   ...OUCH!!!!)

All the original water passages and tubes are present and functioning correctly. The last time I flushed out the water passages was two weeks ago. Only the water passage going to the balance tube was clogged. It was also clogged when I rebuilt the engine three months ago. I have been flushing out the radiator every month now (three times since the rebuild) and now I think I've finally got all the rust and scaling out of the water passages. There was a LOT of rust and scaling in the engine block and radiator!!!

I don't know what else to try. How can I keep the fuel bowl cool enough to not boil the fuel?

....just a thought, and I know it's not closely related, but what if the catalytic converter was clogged? That would cause higher back pressure in the exhaust manifold, which, in theory, would raise temps in the engine bay. Also, what if I put a 170º or even a 160º thermostat in? That could reduce the underhood temp. Or put the outlet from the smog pump directly onto the body of the carbs...

I keep going back to the fact that, from the factory, this car ran!!! I have it almost all original! The only thing that is not installed to make it all correct as fresh from the factory, is the smog pump! I'm just at a loss for any other ideas to make it operate like it did from the factory floor. My last option, and I really don't want to do it because this is my all original 260Z, is to put my spare set of '72 round tops on it. Yes, that will solve the problem, but destroy the originality of it! Dammit! It should run!!! O_o

 

[Captain Obvious]

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.

[tunesnxs]

See! That's what I thought at the beginning too, and that's what led me to try to get the smog pump reconnected and functioning. Vaporizing the fuel in the fuel lines (which happens on my #2 "280" all the time, I can hear the bubbles being forced back into the fuel tank on #2 but not in #3, the 260) because the lines are sitting right on top of the Pipe assembly - Air Gallery, which without the cool air being pumped into the air gallery pipe gets REALLY hot. It only seems natural that such a hot pipe sitting just below the fuel rails would heat the rails enough to possibly boil the fuel in them. However, I do not hear the bubbles in the fuel tank like I do on #2 (the fuel rail on #2 is not insulated, so it gets really hot). I don't think I'm leaning toward the fuel rail "vapor lock" any longer due to the fact that I can just shake the car and get boiling fuel squirting out the vent tube. If the fuel were to be boiling in the fuel rail, then shaking the car would not exacerbate the boiling. I could get some clear fuel hose and install it temporarily to watch the fuel go by, and that will at least eliminate one theory.

The Mechanical, and electric pumps are stock NISSMO pumps, and, asbestos I can tell working correctly. I would be really amazed if one of the pumps were to be causing cavitation in the fuel. There would need to be a serious negative pressure on the down stroke of the pump to cause cavitation and I just don't believe either pump could have enough "umph" to do that.

Now, about that thermostat in series with the water line that goes to the carbs... I have absolutely no idea what you're talking about here. There is the temp sensor right below the thermostat in the bottom part of the thermostat housing, but I think this is not what you are referring to. Other than that, there is only the thermostat housing, the outlet pipe (with three branches), the three hoses that connect to the intake manifold, balance tube, and carburetors respectively.

...and lastly, yes, the car is originally from California. All three of mine are, but #3 is the only one that has any California "stuff" still in/on it. Other than taking the car to a muffler man who will naturally say "Yep! It's clogged. You're gonna need two of those", is there any way to test the catalytic converter to see if it's still good?

I'm also thinking of putting a 170º or 160º thermostat it to help keep the engine temp down.

Edited May 10, 2016 by tunesnxs