Carburetor Re-assembly

This afternoon I rebuilt the carbs using the cleaned-up parts, refurbished bodies from Keith Williams, new nozzles from Z-Therapy, and new floats, gaskets, fuel pipes, needles, banjo bolts, and float screens from Nissan.

I was surprised that the carbs went together fairly easily. Basically it was just a matter of reversing the process I had gone through to break them down. I began with the float bowls. The drain and fuel inlet bolts threaded into the bottom of the float bowls. I used a 12 mm socket with hand-pressure to tighten them. I didn’t want to use to much pressure because the bolts were brass and the bowls are aluminum.

I then tightened fuel-supply bolt up using a 10 mm wrench. Next I moved on to the bolt that attaches the float bowl to the carb body.

One end threads into the bowl, through the rubber grommet and the fitting washer. I tightened this down using a 14 mm wrench.

Then I moved on to the lid of the float bowl. I re-used the old float nozzles, because they appear to be in good shape and the new ones I ordered were the wrong size. I tightened the nozzles into the lid, gently using a 10 mm wrench.

Although the old floats were in good shape, I installed my new floats using the original pins. I made sure the floats on each lid sat in similar positions once installed.

Then I placed the new gasket in place and bolted the lids onto the float bowls using the original bolts. I had wanted to replace all of the bolts with shiny yellow zinc ones but they proved to be impossible to find.

I bolted the assembled float bowl to the carb body using the bolt already installed on the bowl. I used a 10 mm socket on the nut on the opposite end of the bolt. Then I attached the idle-adjustment bolts to the bottom of the carb bodies.

First I threaded in the shaft and tightened it using a 19 mm wrench and then I tightened the knob and spring into the shaft, all the way down to the tightest setting.

On the bottom of the idle-adjust knob I cleaned out the nozzle aperture using a couple of Q-Tips. Then I inserted the nozzle.

I attached the new J-shaped fuel pipe first to the nozzle and then to the fuel-outlet on the float bowl.

Then I installed the new jet needles. I used new N-17 needles from Nissan. In order to set the needles, I used the following procedure on each carb:

  1. Loosen the set-screw on the piston.
  2. Loosely install the needle into the piston.
  3. Drop the piston into the body and push it all the way down until the needle bottoms out in the nozzle (holding the nozzle up tight against the body), forcing the needle upwards into the piston.
  4. Remove the piston and tighten down the set-screw to secure the needle in place.

Then I placed the original plastic washers and piston springs back onto the pistons.

And placed the domes over the pistons and bolted them into the bodies using the original bolts.

Next I replaced the dome caps and fit new fuel screens on the banjo bolts.

And I bolted together the fuel inlet piece and bolted it onto the carbs using the banjo bolt, which I tightened using a 17 mm socket.

Lastly I added the bolt that acts as a stop for the throttle shaft. Here is a picture of the reassembled carburetors.

All that remains is to put the arms that mechanically operate the nozzles back together.

Carburetor Parts Cleaning

This morning I cleaned-up the bits and pieces of the carburetors in preparation for reassembly. I used some Simple Green and scouring pads. After allowing the parts to air-dry I then sprayed on some metal polish and buffed the parts.

Overall I’d characterize the results as “good.” The parts came clean and were sufficiently de-greased. The polish worked okay and some of the parts became nice and shiny. The only problem was in parts that had rust or other blemishes on the metal. This process did not address those types of flaws. Originally I had planned to send many of the pieces off to be sand-blasted and re-coated in zinc. This would have resulted in a much better finish. However, I am too afraid to send all those bits away because they may come back in one big pile and I’d never get the carbs back together again.

Here is a picture of the parts I cleaned and one of the piston springs soaking in Simple Green.

Here are before and after shots of the arm that actuates the choke. You can see the blemishes in the metal remain.

Here are the throttle-adjustment bolts, which came out much better.

Finally, here are the bolts that connect the float bowls to the carb bodies before (left) and after (right).

Fuel Lines, Removal

This morning I removed the hard fuel lines from the frame. I need to strip the frame down in order to clean it up and paint it.

There were two fuel lines that run from the gas tank up to the right side of the engine bay, where soft lines run over towards the carburetors. The smaller (in diameter) of the two lines is the fuel supply line and the fatter one is the fuel return line. Each of the two lines were in two sections, a short section in the front that ran up into the engine bay and a longer straight section that ran back along the frame and curved over and connected to the fuel tank at the rear of the car.

I began by removing the soft line from the front end of the fuel supply line. There was a whole assembly with a fuel filter and fuel pressure adjustment gauge that I removed.

Below is a shot of the front sections of the fuel lines. I first removed the front portion of the fuel supply line. The front and rear sections of fuel line were coupled together. To loosen the couplings I used a 1/2″ wrench to hold the center section of the coupling and a 9/16″ wrench to loosen the coupling itself.

With the fuel supply front section freed up, I disconnected the front section of the fuel return line in the same manner. The flue return line was located just below the fuel supply line. I used a 1/2″ wrench again on the middle section of the coupling, and a 5/8″ wrench on the coupling collar.

This allowed me to remove those front sections of fuel line and start working on removing the rear sections. There was some fuel left in the lines which began to pour out when I started tipping the lines. I caught it in a cup–more fuel for the lawn mower!

The straight sections of the fuel lines were held to the frame by several tabs, which I bent down to free up the lines using a flat-head screwdriver. Above the rear wheels there was a lot of grit built up on the frame over the fuel lines.

You can see where the fuel lines curve around and meet the fuel tank behind the rear axle.

With all of the frame tabs loosened I then pulled the fuel lines back towards the rear of the car, removing them from the frame. I had to work the portions that attach to the gas tank over towards the outside of the frame in order to pull the lines off the frame. There was enough flexibility in the lines to work them off the frame in one piece.

Carb Bodies Return

Well my carburetor bodies didn’t stay in Vegas very long. Keith Williams e-mailed me Saturday to say he had received the bodies and already worked on them. He sent them back and I received them today. They look great and the throttle shafts no have no play in them whatsoever. He also sold me a pair of new throttle return springs, which are NLA from Nissan, for a couple of bucks.

I need to get my act together and get some of the bracket pieces plated so I can rebuild these carbs.

Carb Disassembly

Today I pulled apart my carburetors. I plan to clean them up and replace a lot of the parts, essentially do a full re-build. I need to pull them both totally apart in order to send the bodies off to Keith Williams, who has agreed to rebuild the throttle shaft bushings which tend to wear out over time preventing the butterflies from closing completely.

If I weren’t sending off the carb bodies I would only disassemble one at a time so I’d have a working model in front of me making it easier to put them back together. I think I have enough guidance from my manual and the ZTherapy videos to get them back together, though. I will also probably send out some of the parts to be replated in yellow zinc to make the carbs look brand new.

Here is my box of supplies. It includes my hand tools, a couple of cans of Berryman’s B-12 carb cleaner (very good stuff, less than $6 a can at Walmart), lots of paper towels, and a pair of safety glasses and rubber gloves to keep the carb cleaner out of my eyes and off my skin. I set up a work table on two sawhorses using a sheet of plywood that I placed inside a garbage bag so the wood wouldn’t end up soaked in carb cleaner. Also here’ s a shot of one of the carburetors before I started.

First I removed the throttle return spring, which I will replace with new ones from Keith Williams.

I began disassembling the carbs by unscrewing the dome plunger from the top of the dome, making sure I got the plunger gasket that fits around it.

Next I unbolted the four bolts that hold the dome to the body using a #2 Phillips head screwdriver. I pulled off the dome and set it, along with the large suction spring, aside.

Then I slid out the piston and began unbolting the cover from the float chamber.

I pulled off the float assembly and removed the float chamber lid gasket, which I will replace with a new one from Nissan along with all of the other gaskets. Then I set aside the float chamber and went to work on the carb body.

The way the choke works on the carburetor is this: pulling the choke knob inside the car pulls the choke cable that pulls back on an arm that causes the nozzle on the bottom of the carburetor to move up and down. As the nozzle moves up and down on the tapered needle, more or less fuel is allowed into the fuel/air mixture. I next removed the bolt that connected the spring-loaded actuating arm to the nozzle.

The nozzle is connected to the float chamber, which holds the fuel, by a fuel pipe that I had to remove in order to release the nozzle.

The nozzle rides only as high as the idle adjustment mechanism allows it. This is a spring-loaded bolt that goes up and down when you turn it. The bolt is mounted to a sleeve that threads into the carb body; it is through this sleeve that the nozzle rides up and down. I removed the idle adjust bolt by hand and the sleeve using a 19 mm wrench.

Next I began removing the throttle adjustment arm from the body. First I released the spring that returns it to position and then I used a 12 mm socket to remove the mounting bolt.

Then I pulled the assembly off the body. It is composed of many pieces.

I then removed the float chamber from the carb body. I removed the nut from the end of the mounting bolt that feeds through the carb body using a 10 mm socket. Then I pulled the float chamber off the body with the mounting bolt, which threads into the float bowl, intact.

At the bottom of the float chamber is the fuel pipe connection. I removed this using a 12 mm wrench.

Opposite the fuel pipe fitting is a drain bolt. I also used a 12 mm socket to remove it.

Then I removed the bolt that mounts the float chamber to the carb body. I used a 14 mm wrench and a lot of force to get it off.

Next I focused on the float chamber lid assembly, that holds the actual float. The float moves up and down with the fuel level and operations a float nozzle above it that allows more fuel to enter the chamber when necessary and shuts off the fuel supply when the chamber is full. The fuel inlet had two halves which I separated by removing two Phillips head bolts.

With the inlet separated into two pieces, I then removed the banjo bolt (using a 17 mm socket) and the small screen filter inside it.

I then removed the float by sliding out the mounting pin. I removed the float nozzle using a 10 mm socket.

Then on the float side of the body I removed the throttle plate and the nut on the end of the throttle shaft using a 12 mm socket.

From the piston I removed the needle by loosening the set screw on the side and then I made sure to pull out the plastic washer that sits at the bottom of the piston shaft.

Essentially that completed the disassembly of the carburetors into seven pieces (six for the carb not shown). I spent some time cleaning up the aluminum pieces inside and out using the carb cleaner. I used two full cans, but the pieces got fairly clean.

Manifolds

This afternoon I removed the intake and exhaust manifolds from the engine. Although it took some time, it was much easier given that the body is off the frame. Even so, some of the bolts were difficult to reach.

Mounted on the intake manifold are the carb spacer blocks and then the carburetors and the air filter assembly.

There were two hoses that feed engine coolant through the intake from right to left.

I removed both hoses by first loosening the hose clamps with a Philips head screwdriver. Also, on top the manifold is the bracket that the choke cable actuates to operate the carbs.

I freed the choke cable from this bracket by loosening the Philips head bolt that tightens the upper cable bracket and then loosening the lower bolt that holds the end of the cable. I used a 3/8″ socket on the lower bolt.

I then began removing the nuts that hold the intake manifold on the head-studs. I started with the middle and worked outwards using a 13 mm socket.

After I removed those four nuts the manifold didn’t want to come off, so I started removing the bolts for the exhaust manifold, not sure if there were some fasteners that held both manifolds in place.

I removed the top outside nuts using a 13 mm socket and the top inside nuts using a 13 mm ratcheting wrench because the choke bracket prevented me from getting a socket in there.

There were two lower nuts on the outside of the two inner exhaust runners. I was able to remove these using a 13 mm socket with a long extension.

Tucked-in just behind the outer exhaust runners were two more studs (one each side). The manifold prevented me from getting a socket in there to loosen those nuts, or even a ratcheting wrench over the end of the stud. I had to use a box-end 12 mm wrench to loosen the nuts, and it was slow-going.

But that completed the removal of the hardware connecting the intake and exhaust manifolds to the head. The exhaust manifold had three (at first I assumed there were just two, but there were three) bolts attaching it to the exhaust pipe. I removed each of these using a 14 mm wrench and a 14 mm socket with an appropriate extension.

Then I was able to work the intake manifold off the studs.

And next I pulled the exhaust manifold off.

I took both manifolds out to my stripping station. I then realized that the exhaust manifold is covered with some sort of high-heat coating that is bonded to the metal (it is made of steel while the intake manifold is aluminum). I will probably either leave it as-is or coat it with another high-heat coating because there are some voids in the finish. I did apply a coat of stripper to the intake, which appeared to have the same paint as the heat shield.

The intake manifold cleaned up nicely but will need another round of stripper to be fully clean. Note the shiny copper plugs on top of each side.

Once I’ve stripped the remaining paint the manifold will match the rebuilt carbs (once I rebuild them).

Throttle Arm

Next I removed the throttle arm assembly, which is situated in the rear of the engine bay up against the firewall. It connects at the bottom to the gas pedal and at the top to the choke cable mounted to a knob on the console. On the engine side of the arm is another throttle cable that runs to the carburetors.

Below (left) is a picture of the two cables and where they connect into the throttle arm. I had some trouble removing these cables, which each have a barrel-shaped metal end to catch and actuate the arm. I got some advice from some members of the forums at 311s.org, who could tell that the top of the rod, which is split in half, was cinched together. I was able to get a flat-head screw driver in there and just barely work it apart and get the cables out. Below right is a picture after I removed the choke cable and just before I removed the throttle cable.

The throttle arm itself consists of the vertical rod, upon which the cables mount, and a horizontal crosspiece that feeds through the firewall on both ends, one end onto which the gas pedal is mounted. So stepping on the pedal spins the horizontal rod clockwise and tilts the vertical rod backwards, pulling on the throttle cable and opening up the throttle on the carbs.

The horizontal crosspiece is mounted to the body by two brackets; one on each side. Each bracket has two bolts into the body. I removed all the bolts using a #3 Philips head screwdriver and worked the throttle arm out of the engine bay.

Actually it wasn’t so easy. While I was removing the bolts on the passenger side of the engine bay I dropped my screwdriver, which fell back into the transmission tunnel and rested between the tranny and the body. I could see the yellow on the handle but couldn’t reach the screwdriver from the front (engine bay) or back (down the hole beside the shifter). For a few minutes I thought I would have to do without that screwdriver until the body came off the frame (which makes me wonder what else I will find under there!). But then I asked my girlfriend, who has thin arms, to see if she could reach back there between the head and the firewall and get the screwdriver. She obliged and was able to reach the screwdriver (thank you).

Parts Update

I’ve heard back from my Nissan parts supplier and some of the parts I ordered for my carbs are no longer being produced and therefore no longer available.

I’ve updated the table below that documented my original order (entry dated #19 June 2005#) by adding a column that indicates each part’s availability. Those parts marked “NLA” are no longer available.

Most of the parts are available, which is good news. The rear nozzles are NLA, which surprises me a bit. I’d order two of the front nozzles but fear that the front nozzle may not work on the rear carb. The 2 liter carbs are symmetrical; both float chambers are oriented inward. I’m not entirely certain, but I think I’ll need two opposite nozzles to make it work. Also, the float valves are NLA, as are the screws and washers. I should be able to find similar screws and washers to work without much trouble. For the nozzles and float valves I have a couple of options: (1) just don’t replace those parts, (2) try to get some “new old stock” parts from the roadster parts vendors, (3) see if the folks that re-build carbs for a living have any solutions or suggestions, or (4) see if any other roadster owners may have these parts.