Flatslide Carbs

Flatslide Carbs

Q. So Ken, my all knowing friend. (And I mean that in the nicest way). Do you think that FCR`s are hard to tune?
I am buying a set of 39mm Keihin FCR`s, got them for 500 dollars new in box. Supplied from Yoshimura, with one accelerator pump, set up for 91-95 ZX7`s (should fit right in, on a ZX9 -95 engine!!??) But do I need an adapter plate to fit them to the airbox?? I also need to change the throttle cables, but do I need to change the twist grip, I do not know??
Later on, I am going to buy the APE springs, but what is the matter with the stock retainers. I know the titanium one`s is lighter and stronger, but do I really need them. My mech. told me the ZX11 needed them, because of poorly designed retainers, on higher revs it started spitting shims. NOT GOOD !!
Jay, I know you have warned me, but I could not resist. And I think a set of 39`s on a 950cc engine should be easier to tune, then a set of 41`s on a 750cc, right????

A. SIG, No, not if you have the right needles. Go to www.sudco.com, call them and order the following needles. OCFHP for 39-41mm FCRs. These needles are NOT listed in their catalogue. These are special order from Japan, but they usually have a set in stock. These needles flat work. It is the needle that makes tuning flatslides such a nightmare. The right length, taper etc. Any one can easily tune them for top end with the main, and set pilot mixtures for idle and part throttle transition, but its the needle that everyone struggles with, especially if the one that works best is not even listed. When you get the carbs, see what needles are in there and let me know. If you cant get the OCFHP also let me know and I will see if I can find you a set. There not real expensive, about 30 dollars for the set. I use these same needles in the flatslides on our ZX11 land speed bike and its like fuel injection, SORTED>

Needle in 4th clip position and forget it. 1 accelerator pump means you have REAL flatslides, not OEM Kawasakis, which contrary to popular belief are different. Different taper on fuel mixture screws, different emulsion tubes, different accelerator pump scheme etc., all which has to be changed to make work like the ones I think you are getting. I also disconnect the one pump on the left on the OEMs. Once jetted properly, you don’t need this low speed circuit and it greatly improves fuel mileage. Simply remove screw at top of linkage.

I run the stock OEM 39s, that I bored out to 41. This is another little known trick. You can bore out a eliptical moon shaped chunk of metal on the engine side of the OEMs, then they become 41s.

The reason I use the Ti retainers is because the KAWASAKI RACE KIT retainers are made of aluminium and have limited lifetime duty. I have seen valves pull through these aluminium retainers. However your stock steel ones should be OKAY. Ti retainers are for more revs.

On the ZX11 we used at Maxton North Carolina in the flying mile, on our last run it did spit out 3 shims, 2 exhaust and 1 intake. I attributed this to worn out valve guides, which I later replaced. This motor had over 45,000 very hard miles on it at the time.

Let me see if I got this correct. You have a 1997 Zx7, a 94-97 9 motor and aftermarket 39 mm flatslides for 91-95 Zx7, is this your intended combo?

I have only put the 94-97 9 motor in the 91-95 7 chassis, I have not tried that motor in a 96-00 chassis.

The adapter plates, the 97 RR used similar flatslides, and you should be able to order these parts directly from kawasaki to match the carbs to your airbox. I have put 39mm flatslides on a 93 zx, non r model, and bought the R model air box pieces from Kawasaki and it matched right up. On this model 93ZX7 non R model, the stock twistgrip worked OKAY, did have to change cables obviously.

Smaller 39 versus 41s will give better response in the midrange. However a lot of racers look at this the opposite way. I know of some racers who use the 41s on the short tight tracks because it takes the EDGE off the midrange and makes the power curve more tolerable, and then use the 39s for the big tracks because they can drive out onto the banking at Daytona harder with the midrange the 39s deliver. As most racers say, its the drive out of the corner that matters. I tend to agree.
In most cases, the 39s make as much top end power as the 41s anyway unless you have a really radical motor, looking to breathe at revs up around 13000-14000.

Ken H2Os

Next post is By SigvartArctander
Q. Hi Ken, when you installed the FCR`s on the non-rr, did you have to build some new fuel tubes. From what I can see in the tech manual, there is some differences in the fuel delivery lines. I don`t they come with the carbs, or…????

Next post is By Ken
A. Sig, could be some differences in bikes sold in your country, but engine dynamics being the same for everybody, here’s what you need to consider.

On bikes sold in America, the carbs ram air must also pressurize the float bowls. They do this by using a vacuum switch connected up near the right front side of the frame. This switch is activated off intake vacuum. The best thing to do is to disconnect all this horse shit and do the following.

On your stock carbs you should be able to remove the plumbing going to the float bowl vents and reinstall on your flatslides. This is what I did on the 93 non R I converted to flatslides. This then needs to be routed directly into the airbox.

So in other words, your need to route the float bowl vents directly into the airbox, using parts from your 97r stock carbs and forget all of the rest of the vacuum switch. This by no means has anything to do with the vacuum switch used in the clean air system routed to the valve cover. Totally different set up. This allows the float bowls to stay at airbox pressure, whatever that may be.

This is very important if you are using ram air airbox. If you don’t do this, pressurized air will keep fuel from being drawn up the emulsion tube and major lean out will occur.

I make this same conversion on all ram air 7s I work on and find afterwards I can go to a much smaller Main jet than stock, after removing the vacuum switch controlling air to the float bowls, and routing directly into airbox.

Stock 94-97 9s that I dynoed with pipe and jetting made around 129 Hp. You should get a 140+ with your combo I would hope………..,

I think you will like the 39s just fine.

Ken H20s

Anthony’s notes: Check out this website for tuning FCR’s HERE

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