Stock Carbs

1985 RZ350

Installing the DynoJet Kit

Spec II recommended installing a DynoJet kit and new main jets in the existing carbs. I bought the kit from them thinking it would be a simple process but it was much more...

Once the carbs are out of the bike the first step is to replace the needles in each with the ones provided in the kit. Remove the 3 screws which hold each throttle slide top on. Also please note that I have removed the small spring that goes between the throttle body linkage (green arrow) as it has a tendency to get lost easily.

Now remove the two 7mm bolts that hold each of the throttle arms to the linkage. Once these are removed the throttle slides can move independently from the linkage.

Looking straight down in to the throttle body, you'll see two Phillips head screws that need to be removed. These connect the throttle slide to the arm assembly.

Pull up the arm and flip it over the back of the carb body. You'll be able to pull the slide and needle free of the carb body. Make sure you note where the curved side of the slide is facing for reassembly (it faces the rear of the bike).

The needle is free at this point since the Phillips screws you removed are the only thing that hold it in place. Carefully push the needle through the throttle slide and take note of the way that the spring and plastic clip are placed.

Slide the plastic spacer off the original needle and put it somewhere if you keep things like this. It isn't needed in the DynoJet set up.

Get the new needle from the kit and install the clip. On my instructions it showed it as 3rd groove from the top of the needle.

Reassemble the needle bits without the black plastic spacer used in the original, and place them aside for reassembly in to the carb bodies.

The next step involves the air screws which are set at the factory and then covered with a plug so that they cannot be changed. The DynoJet kit instructions show that they need to be changed so you'll need to remove the plugs shown by the arrows above.

Although it sounds crazy, the easiest way to do this is to drill out the cap. I recommend lightly center punching the plugs and then using the bit included in the kit to drill out the center. The kit instructions also include a big screw used to screw in to the hole and yank the plugs out but I found that both plugs came out on the drill bit. A word of caution - be very slow and careful when drilling. You just want to get through the plug - any further and you could damage the jet.

Once both plugs are removed, thoroughly clean the carbs with compressed air to make sure not of the drill plug metal fouls up any jets. Then use a screwdriver to screw in the air jets all the way. From this point back them out by the required number of turns in the instructions. For mine it was 2.5 turns.

For fun I pulled both air jet screws out and cleared out the passageway with air. Above are the two air screws, springs to hold them at the correct setting, and a small washer that acts as a collar for the spring.

The final step is to replace the main jet of each carb. My kit came with two jet main jet options: A DXP340 main jet and DXP420 main jet. The Spec II F1 exhaust install guide recommends a 290 for a totally stock bike with new F1 exhausts, a 320 for a stock airbox with baffles removed, and a 420 with aftermarket air filter systems. Since my bike is stock I chose the 320 and removed the snorkel and baffles from the air filter box. To get access to the main jet remove the float bowl cover by removing the 4 screwhead bolts holding it in place. When removing the screws note which one holds a guide for the overflow tube for reassembly. Now is also a good time to consider replacing and gaskets, float needles or other easily replaceable parts.

Using wrench remove the existing main jet.....

...and the brass washer it is seated against. Replace just the main jet with the jet of your choice and reassemble with the existing brass washer. Reassemble the carbs in a reverse order of these instructions.

Please note that messing with the jets in your motor can cause disastrous effects if the mixture ends up being too lean. This guide is simply how to replace install the DynoJet kit - tuning it so the bike runs well is a whole different ball game...

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