Smoke and popping, and a few other things

[trogdor1138]

I'm a new owner of a '71 240Z; I've posted on here a couple of times. While the car was in the process of restoration by the previous owner there were periods of long sitting and I am getting everything up to snuff. To help others help me here's what I've done so far:

- Rebuilt transmission with new gaskets, bearings, synchronizer rings, and oil seals. Temporarily refilled with synthetic 75W-90 GL-5 (ouch; I know now), now has Red Line MT90.
- Replaced clutch friction disc, pressure plate, throwout bearing, and slave cylinder
- Replaced distributor cap, rotor, O-ring, breaker points, condenser, and ignition coil with OEM-spec Beck Arnley parts
- Replaced plugs and wires with NGK BPR6ES and NGK wires, gapped per FSM specs
- Dropped fuel tank and had it boiled at a local radiator shop; replaced fuel filter and am currently running a can of cleaner additive through with premium-grade fuel
- Disassembled, cleaned, and rebuilt carburetors with the aid of the ZTherapy rebuild kit and video
- Checked dwell, measured at 37 degrees, timed at 5 degrees (second notch from bottom on crank pulley when viewed from passenger side) with electronic multi-function light

I'm now driving the car daily to and from work, ~40 miles round-trip. I do my best to keep the engine in the 3000 to 3500 RPM range while driving. The car starts well with the now-functional choke, but the choke/fuel nozzle assembly sticks and I'm planning to re-adjust and calibrate this weekend. I know that I've got an exhaust leak under the hood where the twin pipes meet the manifold; it's missing the flange gasket which I've ordered and will also be installing. The rear hatch also doesn't seal quite right and the original bad gas made quite the odor in the car, so I usually drive with my window down. Although the blower motor/switch don't work the control levers are functional and I can get forced air venting through the ducts into the cabin.

This week as I've been driving I've noticed faint white smoke rising from the hood vents (the car has a 280 hood on it.) This morning while making a left turn I also noticed the smoke entering the cabin through the blower vents. I have not noticed smoke from the tail pipe while driving, neither while under load or idling at lights. When I got to work I popped the hood and took a look. I know that I have coolant seepage around the thermostat housing; I'm replacing the thermostat, both its gaskets, and both radiator hoses. I also saw that the frame was wet where the radiator filler neck hose rests near the front driver's side of the engine bay. Finally, there was faint smoke/steam coming from the valve cover breather and where its hose connects to the air cleaner box. Removing the hose cause condensation and puddling of what appears to be oil.

I do get some hesitation/lag when starting from standing in first gear. Once it gets past that point the car will accelerate fine up to highway speeds through the other gears. Deceleration, whether in neutral or gear, often includes one or several backfires or pops, I believe from the tail pipe.

If you've made it through all of that you now know what I do. I've been doing a lot of reading and searching through the forums, but I still have a few questions:

- First and foremost, what should I be looking at for the above circumstances?

- What is the "best/proper" way of setting float adjustment? I do believe that I am running too rich. The video shows the float horizontal at .55 in. while I've read on here about holding the lid vertical and tilting while blowing in the fuel inlet to measure. I sent Bruce an e-mail; maybe they've been busy but I haven't heard back.

- What are common locations for vacuum leaks? The car has a later N33 intake manifold on it with the corresponding emissions-control balance tube. However, no air pump is installed and there aren't any devices installed on the balance tube. Perhaps related, the vacuum tap on the front carburetor is not there. The hole is not plugged, but the residual broken tap appears to be in place in the carb. Instead, a line runs from the manifold vacuum tap to a three-way join, then a line runs to the distributor advance. Does it make a difference which location vacuum is tapped from? Are there any good images showing definitively what needs to be plugged on the balance tube?

- The engine no longer has the coolant line running around the back (firewall end) from the manifold on the driver side to the three-way joint on the passenger side. Instead, the line runs through the manifold and is then capped, with a corresponding cap at the 3-way joint. I am planning to remove the residual line and plug at the thermostat housing instead to eliminate the dead zone; are there any problems with not running coolant through the manifold? The carburetor spacers don't have cut-outs for water flow.

As always, all help is much appreciated.

[Zedyone_kenobi]

Well you can have a vacuum leak from the intake to head, the PCV tube on the balance tube, and the power brake booster line on back of the manifold.

One sure fire way of checking the float level is to hook up a clear tube on the bottom of the fuel bowl. Unplug the coil, and crank the motor over. Then go look to where the level is in the clear hose. You should be a certain level (22mm) if I recall (check the FSM) from the joint between the cap and the fuel bowl.

Adjustments of the float is done by slightly bending the tang that contacts the float needle.

If you live in a cold weather area, the lines help heat up the carbs faster. I live in houston, and like yourself I removed my coolant manifold lines.

[trogdor1138]

Thanks kenobi for setting me hunting further.

I believe (hope and pray) that I am suffering from a bad PCV valve. If I understand correctly the oily fumes from the valve cover are the result of blow-by. This is generally caused by a bad PCV valve, or by wear of the pistons. One is less than five bucks at AutoZone, the other is a weekend project. From what I know the PCV valve is very susceptible to bad oil and engine sludge. This would be in line with the unknown maintenance history of the car and the apparent age of the oil filter. To that end I plan to add some Sea Foam to the oil before driving tomorrow morning, then change the oil and filter on Saturday. Can anyone verify this line of reasoning?

Also, I've seen referenced in several places hooking the crankcase breather to the air cleaner box and the valve breather to the PCV valve (example: http://www.zcar.com/70-83_tech_discu..._622748.0.html) Why would one do this; what are advantages and disadvantages?

Also, can anyone help with the vacuum lines of mystery? As I understand it, and from reading the fiche, the three-way vacuum valve should be connected to the crankcase breather, the air cleaner, and the line to the fuel expansion tank. Instead, mine is connected to the distributor, the intake vacuum tap, and the expansion tank. Where the crankcase breather tap should be there's only a hole left. Should I figure out a way to get vacuum pulling on the crankcase breather again, or is it no big deal?

[Zedyone_kenobi]

Okay first things first.

The distributor vacuum advance should be connected to the little vacuum nipple RIGHT BEHIND the front SU.

The proper location for the large line coming out of the valve cover is the orange air cleaner.

The hose from the crankcase that exists the block right below the dizzy should plug into the PCV valve on the balance tube.

I will check out my three way vacuum valve to see where they are hooked up. One is definitely the expansion tank, I think one is the air cleaner, and the other is the small tube coming off the crankcase vent

[5150 will]

It sounds like Zedyone has you on the right track for Vacuum, etc. As far as your popping/backfiring, you may actually be LEAN on your mixture. Fix one thing at a time though and you'll have a better idea what's going on.