Carb tuning with Ram Air
Q. I’m still in a fight with carbs in my ZX7R and still cant get satisfied, maybe you can make some fresh suggestions.
So: ZX7R 1997 with full Muzzy ti pipe and Factory kit inside. Bike runs lean on the top and tooo lean on the midrange. Airfilter is stock. Main jets 180 and 190(outside and inside).
Got BMC race filter, tried to install it – bike wont run at all, too weak, not good. I suppose that BMC Race makes much more flow than stock that bike gets no fuel at all, just air 🙁
Installed 190/200 mains with BMC. Bike got a monstrous midrange approx at 5000-8000(wheelies easily) but power fades at higher revs.
What should I do?
I suppose that now, when needles go up, the mixture is OK at that midrange, but at top revs, when mains are fully open, there is still lack of fuel. But if I would go for even bigger mains(200/210 sounds mad to me) midrange would be too reach and I should go for different needles or to somehow lower the existing ones?
A. Oleg, here is the secret. There is no way to get a 93-01 RAM AIR ZX7 to jet right. Why do you suppose there are a million questions on this? Why does everyone have a problem with this? The answer is Kawasaki’s solution to the problem in the first place. First there is something called the clean air injection system. This is the valve that T’s into the valve cover that everyone talks about. You can take this off and trash it, or leave it alone, this is “NOT” the source of the flaw. There is however, another valve, that controls the flow of air into the Carb Float bowls. Find this, and remove it. What you want to do is to route a hose from the carb float bowls directly into the airbox. What you want to have happen here is air flowing into the airbox, out through this hose and into the carb float bowls. Use a rubber grommet to get this to seal up good.
You should be able to use the stock pieces to fabricate this hookup.
I’m not even going to try and explain the function of this valve, you will have to take my word for it. What happens is this valve closes off airflow to the carb float bowls under acceleration and on top end, and the end result is it is very hard for gas to come up out of the bowls and thru the main jet. SOOOOOO, Kawasaki puts in these huge main jets, 180,190. Thats a joke. But the fuel flow has such a hard time coming up thru these jets they put these laughable large main jets in.
So, try this. Disconnect this valve and hook it up as described. Then try main jets around 150-160 with your BMC filter. Now that airflow into the airbox is equal to air flow into the float bowls, you can use a more reasonable size mainjet, which also allows you to tune in the needle much easier.
This is the only way to properly jet one of these bikes. On the race bikes they accomplish the same thing by enclosing the entire carb assembly in the airbox, and this is exactly what you will have if you connect your float bowls to the airbox with a straight hose and without that valve. Again, I ain’t gonna try to explain that valve, Kawasaki had their reasons, just take it off, and you can use much smaller main jets.
I have made this mod on at least a dozen ZX7s, works every time. I even did it on one bike that the owner was sure his bike was jetted perfect, and couldn’t believe the difference.