Help with FCR

[thebig450es]

Are there any diagrams or tips on the parts of the carb and where/how to to adjust each circut. Thanks

[ae13291]

what do you want to adjust? are you talking about a FCR carb or a 400ex oem carb?

[Thumpin]

I would go to Jetsrus.com and on that site they should have tuning tips on how to jet that FCR carb, you may have to use like a 07 YFZ to find by model.

By the way whats that 452EX supposta make for power? Sounds pretty stout!

[thebig450es]

Its for the FCR carb.
I need to pick up the engine in a week, we're thinking it should dyno about High 40's/ low 50'sHP

[SHIFTx450]

Not sure if this helps, but I just put on a 39mm fcr with 165 main, 48 pilot, nycQ needle 6th clip down, boyeson quickshot 2, 55 leak, and adjusted fuel screw to where it ran smooth and bike f'n rips

[SHIFTx450]

I built it for my Wife, and when I get on it I still can't believe I am riding a 400ex.

[Thumpin]

I also just bought a 39 FCR for my 416ex and am looking for more tuning info, the YFZ forum maybe a good place to search for info!

The 39mm FCR Carb swap seems like the new hot ticket for the 400ex! Hope more people jump on the wagon! I've got Rossier Engineering found for his richer midrange needle for the carb! See what happens.

[SHIFTx450]

I can't imagine how a YFZ site will help you in tuning a 400ex motor.. I think everyone on here that posts this kinda concern regarding the 39mm FCR swap is thinking too hard about it.. Just put it on and try it!!! Make sure it's mounted properly with no air leaks. And keep a clean air filter as always. My 39mm fcr came directly from my Hybrid CRF motor. I didn't change a thing except move the needle clip position 3 clips richer for more snap and play with the fuel screw to run smoother.. Thing is so smooth yet rips everywhere.

[NacsMXer]

Originally posted by thebig450es
Are there any diagrams or tips on the parts of the carb and where/how to to adjust each circut. Thanks

Fuel screw is on the very bottom of the carb like stock. Recessed way up in a hole. This fine tunes your pilot circuit for changing weather conditions for best off-idle response. Aftermarket extended fuel screw is best as it can be adjusted with the carb fully installed and motor running so you can listen to the motor's response to your tuning.

Idle adjustment is the black knob on a remote cable. I like to zip tie it to the frame for easy adjustment.

Main jet can be accessed with the carb installed, just loosen the air boot clamps and rotate the carb until you can see the big hex plug on the bottom next to the fuel screw. Remove the plug and the main jet is right there.

If you need to change the pilot jet, you will need to take the carb off the quad completely. Remove the fuel screw. Remove all the float bowl screws, pull off the bowl and the pilot will be in there. I don't think your FCR will have a leak jet, but if it does, it will be located in the float bowl itself. The leak jet fine tunes the accelerator pump response.

Needle can be accessed with the carb fully installed. You will have to unbolt/unstrap the fuel tank and rotate it out of the way. Remove the two screws holding the top cover to the carb and remove cover. With one hand, press the thumb throttle wide open to bring the slide to the very top of the stroke. You will see a brass allen head plug in the center of the slide. Remove the plug and you will see the needle sitting in there. Use a thin needle nose plier to gently pull the needle up and out. Move the needle clip down to richen the midrange, and up to lean it out. It should be set somewhere in the middle out of the box but you can tune it for best performance.

Main air jet, and air screw are located underneath the intake bell. Remove the two allen head screws holding the intake bell to the carb body. Should be a size 200 main air jet, you will be able to see the small number written on it. Air screw is next to it, it should be set somewhere around 2 1/4 turns out from lightly seated.

That's about it, there's also the accelerator pump fork adjustment, but I have never messed with it myself. Very easy carb to work on.

[Thumpin]

How does the 200 air jet affect the tune, and that air screw you talk about is differant than the air/fuel screw?

Kinda sounds like the high speed air jets on a holly race carb with an adjustable air screw! Let me know if those air jets affect the wot tune or what.

I follow everything else you explained and have tuned engines up to the air jet part, just tring to understand every detail of the FCR!

Thanx.........

[NacsMXer]

Originally posted by Thumpin
How does the 200 air jet affect the tune, and that air screw you talk about is differant than the air/fuel screw?

Kinda sounds like the high speed air jets on a holly race carb with an adjustable air screw! Let me know if those air jets affect the wot tune or what.

I follow everything else you explained and have tuned engines up to the air jet part, just tring to understand every detail of the FCR!

Thanx.........

Air screws are a pretty common part on carbs, just less often talked about.

If you look at the intake bell on a FCR, you will see two small holes at the bottom. These holes lead directly to the main air jet and air screw if you were to take the intake bell completely off. Air from the intake boot has a direct path in there, and the amount of it is metered by the main air jet size, and air screw setting.

The main air jet works hand in hand with your main (fuel) jet to meter the correct proportion of air into the high speed fuel circuit (3/4 - WOT). Just like you can adjust main jets, you can get different size main air jets, but the size 200 is pretty standard for the 400, so leave it alone.

The air screw is a completely different adjustment than the fuel screw on the bottom of the carb. The correct term for the screw on the bottom is a "fuel" screw fyi, since it fine tunes the amount of fuel going to the low speed pilot circuit. The air screw does the same thing, but for air. It meters the amount of air entering the pilot circuit. Again, you can mess with it, but the setting I mentioned will work fine. That way you can put a pilot jet in there, and fine tune it with the fuel screw only. If you can't get the desired response within a certain range on the fuel screw, you need to change the pilot jet. You might drive yourself batty messing with the air screw, fuel screw, and pilot jets all at once lol.

Here's an excellent writeup by GPracer2500 on how to set up your pilot circuit/fuel screw correctly: http://www.exriders.com/archive/topic/229923-1.html Again, you will need an aftermarket extended fuel screw if you want to try this with a FCR.

[IMSROLL450R]

Nacs your pm box is full.

[Thumpin]

Thanks for your time and detailed break down on FCR tuning Nacs!

[SHIFTx450]

I second that, nice write up and thanks

[NacsMXer]

Originally posted by IMSROLL450R
Nacs your pm box is full.

10-4, try again now.

Thumpin and SHIFTx450, not a problem and glad to help. I'm by no means an expert, just sharing what i've learned along the way.

[thebig450es]

Im thinking of using a 52 pilot jet and a 175 main jet to start off with, does this sound right?

[NacsMXer]

Originally posted by thebig450es
Im thinking of using a 52 pilot jet and a 175 main jet to start off with, does this sound right?

That would be ok, as most likely both will be rich. Mine ran without sputtering all the way up to a 178, but not peak performance. I found best power after stepping down incrementally to a 170.

Didn't you say you're at a little higher altitude? I'm at around 800ft.

If so, you're settings will be leaner than mine since air at higher alt. is less dense.

[thebig450es]

I have a 170 and 165 also, i may try the 165 then

[SHIFTx450]

Originally posted by SHIFTx450
Not sure if this helps, but I just put on a 39mm fcr with 165 main, 48 pilot, nycQ needle 6th clip down, boyeson quickshot 2, 55 leak, and adjusted fuel screw to where it ran smooth and bike f'n rips

Just seconding myself. Try this setup.

[thebig450es]

What type of needle is that and with the quick shot does that make a difference?

[SHIFTx450]

It's the needle that came in the trx450r 2006 hrc kit. I believe it's a yamaha YZF needle.

And I believe in the quickshot. I've heard that if you jet it right you don't need it, for me I really noticed improvement in throttle response snap and in bog elimination.

The 39mm FCR I don't believe comes with an adjustable leak jet. I took the float bowl from my 06 TRX 42mm FCR and put it on the 39mm, put in the 55 leak. Again, the leak jet came with my 06 HRC kit.