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:
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).
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.
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.
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).
Now 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.
Install the rear bracket and screws the same way – following the order in this image.
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.
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).
Once the shaft is installed, tighten the arm screws to lock the shaft into position.
Done! Your carbs should now look something like this.
And just like that, they’re ready to go back on the bike.