I have a major flat spot off an idle and even at mid throttle. I did a search to get some answers and came up with a couple things... one is my filter may not be letting enough air in. I am using a foam filter with pretty heavy oil. Two - the mod done to the accelerator pump, because the way it is now it is pumping to much fuel in?? When I first put it on and heard the flat spot, I thought it wasnt getting enough fuel, but what I am reading is its getting too much and not burning it. Does this sound right? How do I mod the accel pump, am I shortening the amount that it can pump? Any help is appreciated and thanks!

 

Try getting "zip ty racings" air mixture screw. It is a new air screw with alittle **** that you can adjust while warming the engine up. I have bought one but haven't installed it yet. I have had several people tell me, that this is the secret to the fcr. I have the fcr for my stroker, but the engine is getting a new piston right now. When I put it bach together it will have the new air screw. If it doesn't pull out the flat spot, the $500 carb will go BYE-BYE. I am sure it'll be better, though.

 

I have heard of those, I will give it a shot. Thanks and good luck with yours!

 

I am assuming that this carb is for your 400ex. Where is your jetting at?

 

Yeah it's for my 400ex... I am at 180 on the main and 52 pilot. I was running a 180 in my stock carb and it ran great and the plug looked fine. But from what I read in past posts, I am thinking a$$ backwards of what the problem is. I am thinking not enough fuel, which causes the flat spot and from what I read it is too much fuel!!

 

A flat spot is usually a lean condition.

 

more than likly is leaning out a lil

 

If you have a flat spot on the bottom, then put a bigger slow jet in. If it is flat in the mid range then raise your need. Try the slow jet first. Also do you run your airbox lid on or off? You can adjust your accelerator pump also, but start with the slow jet. I think mine is at 55, but I can't take my float bowl off this second to check because I don't have the right size allen wrench. My is 440 big bore, full FMF, cam, port, K&N (without air box lid or with breathable cover depending on where I am riding)

 

Also, what elevation do you run at?

 

I don't think it's lean, but on the contrary, rich. I had the same problem when I put an FCR 40 on my Z440, and it turned out that the needle was the cause of the whole problem. What clip is the needle on right now (from the bottom, or tapered side)?

I doubt the Zip-ty screw will do anything at all. I have one, and while it does make things easier, you won't see any change by buying this part.

I want you whole jetting specs...so far I've got- 180 main, 52 pilot (which sounds too fat to me), ??? on the needle and ??? on how many turns on the air/fuel screw.

Trust me, I've rejetted this carb about 500 times, on alcohol and gas, and once you get it figured out, you'll be happy you bought the carb.

BTW Tractorpacker- why did you pay $500 for the carb? FCR 40mm's can be bought for $340 from Service Honda...sounds like you got ripped....