jetting an FCR

[EX 80]

I am just wondering what you guys have yor 39mm FCR's set at for you 400ex, and what mods you have. I have 416 JE piston 10.8:1 , XR400 cam, mild porting, stock head pipe, yoshimura race slip on, K&N filter with 10 1 inch holes in lid of air box, and FCR carb. Right now my carb has a 168 jet, and the pilot jet it came with, i don't know if this is normal or not but when its idling before its warmed up, i push the throttle quick to wide open and quad just dies, but once its warm this goes away. Does any body else's FCR do this?

[Leo]

FCR Gurus, help him out... and remember that really great answers get moved to the 'best of' forum

Leo

[wyndzer]

I have my FCR as follows 165 main, clip on needle moved down one position and the next size up pilot than stock, I think 54? Mixture screw about 1.5 turns out. Mine starts great when cold. I am thinking of going to a 168 main though.

[NVR2L8]

Keep in mind that jetting depends on what individual mods we've done to each our machines, as well as the elevation where we are located...even identically modded engines at or near the same location can have slightly different jetting settings.

Having said that, my 400EX has been modified similarly to EX 80's, and includes a 416 JE piston 10.8:1 , XR400 cam, mild porting, stock head pipe with internal welds removed, FMF Power Core IV "Q" slip on, K&N filter with modified air box lid, and 39mm Keihin FCR carb. At about 500 feet above sea level I'm running with a 52 pilot jet and fuel screw 2.5 turns out, needle on the third position, and a 165 main jet (it also runs nice and brown with a 162 also, so I might drop a size on the main). With this set up it seems to be running very well, and starts up easily after a few pumps of the throttle. In fact, it starts and idles better when cold than when it was stock! I should also mention that I run a 50/50 blend of 92 octane Chevron and 111 octane leaded Union 76 race gas.

Anyway, I'd have to say it's somewhat normal for your engine to hesitate and/or die if you punch the throttle when cold, but if it were my machine I wouldn't be cranking too hard on the gas until it's good and warmed up! At any rate, since it only does it when cold you might consider taking a look at what size pilot jet you are running...my guess is you need at least a 52. Also, if you can somewhat lessen the hesitation by turning the fuel screw out, that's a good indication you could go a size larger on the pilot.

[nakomis0]

My Fcr dies when you hit the throttle also. Just needs to warm up.