Rebuilding Carburetors – 1999 Nighthawk 750

Part 4: Carburetor Combination

The carburetors are shiny clean and reassembled. In this post, I will explain how to put them back together.

As a reminder, this is the order in which the carbs go back together:

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You may have wondered what all the extra o-rings in your carburetor kits are for – they go on the joint pipes that connect the carburetors to each other. If you haven’t done so, remove the old o-rings from the joints and install the new ones. In the photo below, I already installed the new o-rings (red arrows).

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If you take a closer look at the pile of old o-rings, you’ll see many of them broke when I tried to remove them. The rubber had practically turned into hard plastic over the course of 16 years.

Okay, now that that’s done, it’s time to combine carb #1 and carb #2. Start by installing two-way fuel joint pipe (1), the three-way air vent pipe (2), and the thrust spring (3) between carb #1 and #2.

Honda Service Manual - 91-99 CB750

Once the joints are in place and the carbs are connected, install the synchronization spring (4) – the fat spring and the synchronization screw go into the top of the bracket, the skinny spring goes in between the two brackets:

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Don’t worry about the position of the synchronization screws for now, just make sure they are seated securely. You’ll adjust the screws during the carb synchronization process – when the carbs are back on the bike.

Next, combine carbs #3 and #4 the exact same way: two-way fuel joint pipe (6), the three-way air vent pipe (7), the thrust spring (8), and the synchronization spring (9).

Honda Service Manual - 91-99 CB750

Next, it’s time to connect the two carb pairs. Start with the three-way joint between carb #2 and #3 (also see schematic above), then install the front bracket and screws loosely. Place the carbs on a flat surface with the front side facing up. Press them together carefully and tighten the front bracket screws in the sequence shown below in two or three steps to prevent carburetor misalignment.

frontbracket

Install the rear bracket and screws the same way – following the order below:

rearbracket

Almost done! All that’s left is the installation of the starting enrichment valve (choke) arms and shaft. Slide the arms onto the valves and push the shaft through the arms and the designated hole in each carb.img_1411a

The arm for carb #3 is also the bracket for the choke cable. It comes with a little spring – check out the photo below to make sure you install the spring correctly. The extension on the spring hooks into the side of the arm (yellow arrow):

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Once the shaft is installed, tighten the arm screws to lock the shaft into position.

Done! Your carbs should now look something like this:

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And just like that, they’re ready to go back on the bike.

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Rebuilding Carburetors – 1999 Nighthawk 750

Part 3: Carburetor Disassembly

The carburetors are off the bike and separated – what next? In this post, I will explain how to disassemble the carbs so they can be cleaned.

Before you get started, make sure you have the following items:

Carburetor kit

Four carburetor rebuild kits – I bought them online for $16/kit.

Carburetor kit

Cleaning supplies: Simple Green, a can of WD40, at least two cans of carb cleaner, an old tooth brush, a small brass wire brush, and fine steel wool;

If your carbs are really old, grimy and/or rusty, generously cover bolts and exposed threads in penetrating oil (I use a brand called Liquid Wrench) and let them sit for at least one night. Your patience will pay off, I promise. Continue reading Rebuilding Carburetors – 1999 Nighthawk 750

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1992 Nighthawk – Petcock Assembly

I took the Nighthawk’s fuel petcock apart to clean it, and  —after I was done— realized that I didn’t know how it goes back together. I checked the repair manual, Honda’s general service manual, and Google for assembly instructions, to no avail.

After some head-scratching, a fresh pot of coffee and some try-and-error assembly attempts, I finally figured it out. It’s not rocket science, of course, but I decided I should do my part to close this tiny little internet knowledge gap. So, here it goes:

This is a Keihin petcock from a 1992 Honda CB750 Nighthawk – all disassembled. By the way, this pile of scrap metal is worth a whopping $215 (check it out on BikeBandit).

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Feel free to comment on how clean the parts are. Took me 3 hours of soaking, scrubbing and wire-brushing.

Continue reading 1992 Nighthawk – Petcock Assembly

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1992 Nighthawk – Take 3

Argh, this bike is going to my downfall. Every time I pick up a wrench to do one small thing, I end up wrist-deep in motorcycle guts.  Meanwhile, laundry and dishes are piling up everywhere, the backyard looks like a jungle, and the only thing left in my fridge is a stick of butter. And I haven’t blogged in two weeks.

So, here’s a recap of my latest grease monkey adventures.

First up: The oil change — or: Things that stink, for 500.

Oil for the bike's belly, beer for mine.
Oil for the bike’s belly, beer for mine.

I am not sure what I expected from 20 year old oil, but I didn’t think it would smell as bad as it did. It was black, felt like what you find at the bottom of a french press coffee maker, and had a nasty smell to it. After draining the old oil, I “rinsed” the engine with a liter of fresh oil until the oil came out looking like it did going in. Continue reading 1992 Nighthawk – Take 3

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1992 Nighthawk – Take 2

Today is spark plug day!

After sitting in a parking lot for 14 years, the Nighthawk’s spark plugs had developed a bit of a vintage look, to say the least. I soaked  them in Liquid Wrench penetrating oil for a few days, and now they look good and ready to meet my favorite tool: a two foot wrench and a 18 mm spark plug socket.

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The oil bath was definitely a good idea, the plugs are coming out surprisingly easy. I am a little worried about the crusty ports, the penetrating oil knocked a lot of the rust loose and I am not sure how to prevent it from dripping into the engine. Continue reading 1992 Nighthawk – Take 2

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1992 Nighthawk – Take 1

I really shouldn’t ever go on Craigslist. I mean, I almost never do but I did last weekend and found an old, neglected 1992 Honda CB750 Nighthawk with less than 12,000 miles under its belt. And for whatever reason, I immediately wanted it.

The tags expired in 2002, it’s been sitting in a parking lot somewhere in Maryland ever since. For some reason, the owner decided to get rid of it now, brought it to friends who run a Honda dealership in Virginia and they sold it to me for $600.

1992 Nighthawk

This bike has literally not been moved or touched in 14 years. It’s crazy to think that the last time this bike was out on the road, I was a second-year in college.

This is where my journey with this bike begins – and I invite you to come along. Advice, suggestions and smartass comments are, as always, welcomed and encouraged. Continue reading 1992 Nighthawk – Take 1

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Rebuilding Carburetors – 1999 Nighthawk 750

Part 2: Carburetor Separation

The carburetors are off the bike – what next? In this post, I will explain how to separate the four carbs from each other. FYI, I took the photos while I put them back together – that explains why the carbs are so clean and shiny. They were much (much!) dirtier when I took them apart.

Before you do anything else, put a piece of painters tape on the top of each of the carburetors and number them like this – it’ll save you a lot of headache later:

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The separation process begins by separating carburetors 3+4 from carburetors 1+2. Here’s how you do that: Continue reading Rebuilding Carburetors – 1999 Nighthawk 750

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Rebuilding Carburetors – 1999 Nighthawk 750

Part 1: Carburetor Removal

Most modern bikes are fuel injected – our Triumph Speed Triples are. But the 1999 Honda Nighthawk and the 2004 Honda Hornet are carbureted. Both bikes feature four carburetors (one for each cylinder) … delicate little devils that don’t require any of your attention – until they do.
Carbs like to be synchronized, and eventually, they will demand to be rebuilt.

This three-post series explains how to remove, separate and rebuild the Nighthawk carburetors. Note that no matter how ambitious you are, this usually turns into a multi-day project … though it could be done in a day, I suppose. Make sure to order a rebuild kit (which is basically just a set of replacement gaskets) before you get started. And when I say “a rebuild kit”, I mean: one for each carburetor.
So, in the Nighthawk’s case, I needed four.

In case you’re not sure – the carburetors are tucked in between the air cleaner and the cylinders:

Carburetors

Continue reading Rebuilding Carburetors – 1999 Nighthawk 750

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