Jetting Survey for 40mm FCR Carb

[Quadzilla]

For those of you with the 40mm FCR carb on your 400EX, please provide the following:

Main Jet: 170
Pilot Jet: 42
Needle Jet Setting: 2nd from the bottom
Fuel Screw: 2 1/2 turns out
Motor Displacement: 416cc
Compression: 11:1
Cam: Hotcams Stage II
Porting Work: Yes, mild porting
Valve Work: Yes, mild - freshened up 3 angle
Pipe: Sparks X-6

I would ignor my jet sizes above because I just got the carb and will install mine tomorrow. I obviously have not had time to tune it. I'll post my results this weekend. Please provide your information so that I and others on the site will have a good starting point. Thanks much!

[cals400ex]

your not running a 39 anymore either??

well, i have a 40mm fcr also but it isn't on the bike yet. i imagine it won't be on for 2 or 3 weeks. i am in the process of rebuilding my bike and i will get my cylinder off tomorrow hopefully and ship it in for the new sleeve to be installed. however, i have been talking to a jetting expert for dirtbikes. well, he rides honda so he extremely knowledgable with the fcr 40's from the crf450 bikes. he said the needle has a huge difference in what mainjet will be needed. he mentioned it can be a difference of running a 165 mainjet with one needle and a 185 mainjet with another needle on the same bike. he went on to say some needles will provide better power down low and others are for top speed. of course, there is a bunch inbetween. i want the high speed power so he put in a lean needle which said i will need a 180 to 185 main jet and this will allow for more top speed. i really never knew it worked like this. he also sent me two other needles made for this carb when on a dirtbike. i told him my bike won't have near as much power as one of those crf's is pushing. i honestly don't know where he set the clip position at. these needle's have 7 positions instead of 5. he put in a 45 pilot jet for me.


now, he said this was going to be a guess because he is an expert for tuning in bikes, not atvs. yes they work similar but he just has never tuned this carb in on a 400ex. i will let you know how it goes when i get things together. i imagine i will have to do some major fine tuning but that is how these aftermarket carbs are.

what did you do to the intake to make the boot reach the carb?

[Quadzilla]

Well, for the boot, moving the airbox was not enought. It almost reaches the carb but the airboot hits the frame crossmember which prevents it from quite getting onto the carb properly. I could have streched it a bit, but didn't trust it to stay on. So I went and got the exhaust pipe and radiator hose. You will need a couple inches of 2 1/4 OD (not ID) exhaust pipe to make this work. I bought both (OD and ID) because none of the posts specified which to use. Another thing to watch is that the radiator hose is a little large for the opening on the carb. I make a cut on the end of the hose that was about 1/8" wide buy 1/4" long so it would pinch together and snug up better to the carb. Don't make it too long or it will cause an air leak.

It also seems that the 170 that came with the carb is too lean for my motor. I put in a 185 and it's still a hair too lean. My friend went to a shop today and grabed a 195, 200 and 205 for me and is stopping over later to drop them off. I guess the valve job and porting are causing my motor to suck a little more gas than some other motors on here. I noticed that on Z400 central, it's not uncoming for those guys to run a 180 - 205 on those motors depending on build. Unfortunatley, I have not seen too many guys running the 40mm FCR's here. At Z400 Central, a lot of guys on the Z's are running them and as I said above, with large main jets. Maybe the 40mm likes larger jets vs the 39's? Don't know. Oh the 400mm is a lot wider than my 39 fcr. It's pretty different looking. They changed them quite a bit from the older 39's and 41's. More on all this after I get it jetted right.

[cals400ex]

yeah, let us know the details when you get it up and going.