39fcr jetting

[davidhoe]

I need a starting piont for jetting a 39fcr on a
440 11-1 comp.
TC924 mx cam
ported and polished head
and open air box
in VA close to sea level

Thanks in advance

[drew416ex]

I have that carb on my 440 stroker. I have a 200 main, 48 pilot, needle in middle slot.

[katch26]

what makes you guys run such large mains on the fcr? Most 450's are unning in the 160 (not bored). The one I put on my pred is dialed in at 167. Just curious

[sprayedgt]

I think it all has to do what works for your particular combo. Like you said, dialed in. Not all bikes with the same mods can be jetted the same way. I would say a built 440 with head work and a cam would def need more fuel than a 450 with bolt ons.

[drillteamleader]

carb jetting has a lot to do with how much vaccume signal the carb recieves. If you have a cam with a lot of valve overlap you will need bigger jets to flow the same amount of fuel as you would with less overlap.

[drew416ex]

Originally posted by katch26
what makes you guys run such large mains on the fcr? Most 450's are unning in the 160 (not bored). The one I put on my pred is dialed in at 167. Just curious

Drillteamleader and srayedgt are both right about this. It all depends on your setup. The only way to truly dial it in is to get it dynoed with a sniffer so that you can see your air fuel ratio. I got mine done and those are the jets that it required.

[2muchquad]

I just installed mine a couple weeks ago.I have a 165 main,and a 40 pilot.I am running a dyno jet needle from a yz400f jet kit,3rd slip from top.It runs real good right now,throttle response is crisp:)

[katch26]

Originally posted by 2muchquad
I just installed mine a couple weeks ago.I have a 165 main,and a 40 pilot.I am running a dyno jet needle from a yz400f jet kit,3rd slip from top.It runs real good right now,throttle response is crisp:)

see that sounds more right to me but you guys know more about the 400 than me. Not bashing in any way, I just think it amazing the differences in jetting.
These are all on standard 39's right?, not bored correct. I have seen the big variance going to larger bored FCRs but never going from just one setup to the next. Just asking because I love the way the carb runs on my bike and have been seeing the 39 going for dirt cheap and wanted to pick one up for the 400

[davidhoe]

I ended up with a 50 pilot, 200 main, and needle in the middle.

[NacsMXer]

All mods in my sig with the FCR 39 I run a 52 pilot, 168 main, and EMP needle with clip in the middle.

It's crazy you guys run 200 mains, once I hit a 170 main my plug is black. 165-168 is about the sweet spot for mine. No two motors are the same however so dial it according to what it needs.

[2muchquad]

i dont even think mine would rev up with a 200 main:)

[davidhoe]

The porselen on it is white all the way till the base were it is a lite brown. I tried a 175 main took it for a ride ( wide open and killed the motor at wide open throttle al pulled the plug and there was no smoke ring at the base and had a lite powder on the plug so I put the 200 in it and it was damn nere perfect. I'll have to check on the needle but it has 7 notches and 2 turns out on a/f screw.

Also found out you can run a accelerator pump diaphram off a crf450 and will shot alot less fuel it has a 4.1mm revit so you don't have to use a washer or r/c car retainer, it was only $17 with the o-rings, spring, and new ap cover.

[jt53142]

I'm at a 170 main, 42 pilot, 2 and a half turns out on the fuel screw, ncvq needle (these are off 2004 yz450f dirtbike) 3rd notch down. I also put an o ring around the AP. If you have any bog the ncvq needle is the best solution. My carb was off a yfz450 but is a 39mm fcr.

[2muchquad]

I put the 200 in it and it was damn nere perfect.

yeah everybodys is different,you may have a needle with a fatter taper on it,therefore requiring a bigger orfice(jet).