"Jetting"

The document you are reading is only to be applied to Road Racing motorcycles and is not intended for street legal vehicles. The author nor the host of this web cannot be held liable for anything you do because you read this.

Now that that's out, this page is all about jetting a motorcycle. I will only apply one set of jets and make one series of adjustments. The motorcycle that this paper demonstrates is a California model 2002 Kawasaki zx-7r. The "Jet Kit" applied is by Factory Pro. For the series of pages I will cover California emissions removal, Adjusting the carburetor float height and a modifcation known as "The float bowl mod" as gleaned from the vast resource known as the zx7r Owners Club Discussion Forum, Perhaps the greatest motorcycle resource known to man.

Step 1 - Preparation

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Airbox
Remove the gas tank and air filter until you are looking at the bottom of the airbox.(Upper Right) Clean out the inside of the airbox while you are in here, there's no time like the present. Disconnect the the PCV hose from the bottom of the airbox. (Upper Left)Turn out the three screws and remove the airbox (Lower Right).

Put all the screws in a box and get them out of the way! You won't be seeing them for a few hours so the further the better. (Lower Left)

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Step 2 : Smog

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Smog
Removing the California Emissions from your streetbike is illegal. For race applications tho, it's all good. The California emissions is a bit more complicated than the 49 states setup(upper left), but you might notice that they have only added an evap system to it (Upper Right). Other than that I can't tell a difference. What we will be removing is everything emmisions, short the PCV hose that is mentioned above. When everything has been removed join the two reed plate hoses at the top. You can also buy a block off plate from Muzzy's or some other race manufacturer. When you have removed all the smog, you should have a box of junk similar to the one on the right, because I intend to put the smog back on, I will be keeping all the gear.

[Click to enlarge image]Finally, plug off the four vacuum lines that go into the head benieth the carbs: Use 5/32" plugs.

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Step 3:Float Bowl Mod

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Ken Waters' Patented "Float Bowl Mod"
This modification is the brainchild of Mr. Ken Waters, who was clearly a brilliant technician who has passed away in an unfortunate accident. I don't know much about his passing. Speculation is that the accident was not motorcycle related. Reading thru Ken's posts on the Zx7r Owner's Club Discussion Forum has helped many motorcycle owners, and myself, understand a load more about how bike tuning is done.

Principle: (As paraphrased from Ken Waters)
In order to get the pressure in the float bowls equal to the pressure in the airbox, racebikes enclose the entire carb assembly in the airbox. As logic, fate would have it we are supplied with little hoses that run into the float bowls of our carbeurators. We are going to exploit these hoses to ballance the preasure throughout the fuel system.

Situational Information:
Now, as if knowing the two hoses that appear to come from the top of the carbs and indeed are attached to the top of the carbs are the ones we are going to use isn't confusing enough, I'm going to tell you that they are connected directly to the float bowls which are at the bottom of the carb assembly. When we pull the carbs off later you will see that the tap is at the top, and the orifice is in the float bowl.

Application:
It's real easy. Just connect the two hoses that are discussed above directly to the airbox. There are many opinions about how to do this, I chose to destroy as few parts as possible in an effort to keep as many of the stock parts in tact as possible. I melted one end of a leftover vacuum "T" shut (Upper Right) and connected it to the hose that used to connect the evap cannister and intake silencer to the airbox(Upper Left). Again, trying to keep as many stock pieces stock, I plugged off the other line to the airbox with a screw(Lower Right). I do however, suggest using this other line to connect there, as it can provide a better seal to the airbox. I compensate for this by using a hoseclamp on the one I used.

Note: No matter how you connect it, connect the line where the clean air is, between the air filter and the carbs.

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Step 4: Install and Adjust

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Finally We Work The Carbs!
Disconnect the fuel line where it t's off into the carbs.(1) Open the throttle assembly on the handle bars and let the slack out of the throttle cable there. (2) Pull the two throttle cables off the carbs and lift the throttle cables from their pirches. Loosen the four mainfold clamps and remove the carbs by pulling out and up at the same time. (3)

Once they're out, turn the carbs upside down on the work bench and remove the sixteen screws that hold the float bowls on (4) and remove the float bowls. Place carb assembly on its side to remove any pressure from the floats and measure the float height with the floats resting lightly on the float pin so as not to push it in at all, but not rise above it either.(5) The floats stock should mesure 13mm. We need to change this to 15.5mm for our Jet Kit. Do so by bending the little tab between the floats and the float pin. (Right)

After you've adjusted the float hieght, remove the main jets and emulsifier tubes and replace them with your choice of factory mains and tubes. I chose the 168 outer / 178 inner (Smaller) combonation because of my altitude.(6)

Remove the four black caps on the top of the carbs. (7) Be careful because they are spring loaded! Remove the needle jets and place shims "as necessary" (Consult with Factory Pro or a tuner in your area about this.) My favorite wrench jockey suggested two shims and so far it seems he was right, response is genuinly smooth all the way through. Replace the stock springs with Factory springs if provided.

To finish of the mods, I added a 4 degree Factory ignition advancer.(8) An easy install that smoothes out throttle response even further.

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