stock yfz carb on 400ex

will this work? it is an fcr 39mm which you can buy aftermarket for the ex. i know you mite have to do some mods for it to fit but otherwise is the inside like the aftermarket for the ex? thanks

[aviator4]

Yes, it will work. it's a tight fit in there, but it will work.

You will have to make an extension for the EX'es intake boot, and space the gas tank up with some foam in order to get it to fit. the intake book from the carb to the engine is a TIGHT fit, but you can get it on there. The YFZ carb as two "nipples" on the ports to fit on the stock YFZ boot, but the EX boot doesn't have 'em. I would assume you could file them down, but I didn't need to in order to get a good seal between the EX boots and the YFZ carb.

If you do this mod, be ready to spend more time jetting the bike. The bowl of the carb sits VERY close to the starter on the EX, so getting a wrench in there is a considerably harder than on the stock carb. You could get around this by modifying your intake boots and moving the carb forward, but I haven't done it.

You will also need the stock YFZ throttle cable. It fits in there just fine. the OE honda cable WILL NOT work with this carb. (once you get the new carb, you will see why).

Some other things to think about on this mod.

a Stock YFZX carb will make the 400 hesitate right off the throttle. This is more prevalent when you "floor" it, but can be solved by using an aftermarket accelerator pump from Curtis Sparks (I am sure that there are other companies that make it as well). Once you're into the throttle a little bit, the problem goes away without the accelerator pump.

Also, the stock YFZ carb will have to be jetted WAY down. I went from a 158 main on my stock carb all the way down to a 142 on the YFZ carb before the mixture was right. This was done on a dyno, so I know it's right. It was still a little rich, but that was the way I wanted it because I run nitrous.

You will also notice a little "whistling" from the carb at about 1/4 throttle. This is normal and doesn't affect performance.

The other thing I really noticed was that the throttle is MUCH stiffer. The springs in the YFZ carb are heavier than the EX carb. I got arounf this by putting an aftermarket throttle on my bike.

The power band will move significantly when you do this mod .It moved my peak UP the RPM band almost 1,000 RPM, but it stays at the peak longer.

I gained 4 horse from this mod.

thanks a bunch aviator!

[2muchquad]

[QUOTE] Stock YFZX carb will make the 400 hesitate right off the throttle. This is more prevalent when you "floor" it, but can be solved by using an aftermarket accelerator pump from Curtis Sparks

this problem is easily rectified by removing the right side cover,you'll notice the tab for the plunger,well next to this you'll see a "pad" where a set screw is used on certain models.drill and tap this for a adjustment screw which will control how long the fuel "squirts" from the accl. pump.its really easier than it sounds.the problem is too much fuel is getting dumped into the motor on intial throttle opening.with this mod you can vary the duration of the squirt.stock is almost 1.6 sec,i went for something like 1 sec,the results were huge,this is "factory race team level" throttle response her:D

[aviator4]

Any idea where I might find some photos of this mod? I'd like to see what you're talking about without tearing my bike apart.

What size screw did you end up using?

[2muchquad]

Detailed Procedure on the BK Mod

[2muchquad]

http://motoman393.thumpertalk.com/tech/carbinfo.html





try this:)

[aviator4]

Okay,

I was so excited about this mod that I rushed right out to my bike and proceeded to take the side access panel on the right of the carb off to see what I could see. In the picture below, the top image is from the link you provided, the bottom is the carb on my bike. Obviously they are different.

Now, I KNOW that the carb I am using came off of an 05 YFZ, I saw the guy take it off. However, as you can tell, there are some serious differences between the carbs that make this mod infeasable for my carb.

The "detent" that you are supposed to drill is replaced with a side case bolt hole that is tapped to accept the allen head screw.

There is no place to put the screw in this application. I think this mod only works for the older series FCR carbs. The newer model carbs are different (as you can see)

If you were to try to drill a hole in the side to accept a screw, it would be so close to the edge, it would break right out as soon as you tried to tap it, not to mention putting tension on it with a screw.

Sorry man, I don't think you're mod will work anymore.... which sucks for us. :-(

[2muchquad]

man that sucks,i dont know about the new carbs but it works wonders for the older fcr carbs which are still in HIGH demand.i cant touch one for under $250 on ebay yet,and im a ebay pro.:D
try thumpertalk and see if anybody has com up with something for the newer carbs,thats where i learned about this,or get yourself an older carb:)

[DUNEZRUNNER]

Have you tried replacing the LEAK jet on the yfz carbs to eliminate the hesistation. It does the same thing as putting a new accelerator pump cover on the carb. It is just a cheaper way to do it $10 compared to $80. On the yfz forums people are changing them to eliminate the bog in the yfz, I imagine that you could do the same for the EX but just have to make more of a change. I have read about it on YFZcentral.com and am planning on doing this to my YFZ. Hopefully you can do the same to your EX.

Thomas

[aviator4]

Thats a good question. Can you supply a link to the leak jet mod?

[DUNEZRUNNER]

http://www.yfztech.com/forum/index.php?showtopic=3958&hl=leak+jet

This link seems to be the best one that I can find on explaining the concept. Inside the link there are 3 other links with detailed instructions on how to do this adjustment. It is for the yzf dirtbikes but the yfz is the same, the jets sizes are probably a bit different and yours will be alot different. This should be plenty of info on it but if not you can go to YFZCENTRAL.COM or YFZTECH.COM and search LEAK JET and you will get alot more info.

I hope this helps

Thomas