fcr jetting for 1000m 3000ft

i think i have finally worked out why my bike is running so rich,its because i ride at an altitude of 3000ft. i am running a 45 pilot jet and a 100 pilot air jet. should i drop down to a 42 pilot jet and if so what should i change the pilot air jet to. bike seems to pull cleanly through the rest of the rev range,i am running emn needle 3rd clip and a 155 main jet but if you guys have any other jetting suggestions i would like to hear

What engine mods? Pipe?what kind of fcr?

Edited by mickeydee

Due to my crystal ball not working you will need to supply more info ....

 

To add to the above , is pipe corked or open..?

 

I am guessing Fcrmx ?? but that's where I stop without confirmation and the info requested .......

sorry guys. its a slant body fcr from a wr400, the pipe is the original but its been modified to run a straight through baffle, i have done the 3x3 mod. i'm using the r&d flex jet currently set at 2.5 turns out. there are no engine mods,its completely standard. at around 1000 metres it has a really bad flat spot from idle to 1/3 throttle. if i close the throttle quickly from wide open i get a loud pop or backfire,during deceleration it pops very badly through the exhaust and this decreases as altitude decreases

sorry guys. its a slant body fcr from a wr400, the pipe is the original but its been modified to run a straight through baffle, i have done the 3x3 mod. i'm using the r&d flex jet currently set at 2.5 turns out. there are no engine mods,its completely standard. at around 1000 metres it has a really bad flat spot from idle to 1/3 throttle. if i close the throttle quickly from wide open i get a loud pop or backfire,during deceleration it pops very badly through the exhaust and this decreases as altitude decreases

 

The popping on decel is normal......can you post a pic of the carb, I thought stock WR 400 carb was FCRMX....

Edited by Craigo 485sm

The popping on decel is normal......can you post a pic of the carb, I thought stock WR 400 carb was FCRMX....

stock yzf& wrf 400 and 426 carbs are slant slide fcr's

sorry guys. its a slant body fcr from a wr400, the pipe is the original but its been modified to run a straight through baffle, i have done the 3x3 mod. i'm using the r&d flex jet currently set at 2.5 turns out. there are no engine mods,its completely standard. at around 1000 metres it has a really bad flat spot from idle to 1/3 throttle. if i close the throttle quickly from wide open i get a loud pop or backfire,during deceleration it pops very badly through the exhaust and this decreases as altitude decreases

try a smaller main jet. Start with a 150 mj. I used to run a. 155 mj at 1400 ft and I was using a yosh full ex system at the time

sorry guys. its a slant body fcr from a wr400, the pipe is the original but its been modified to run a straight through baffle, i have done the 3x3 mod. i'm using the r&d flex jet currently set at 2.5 turns out. there are no engine mods,its completely standard. at around 1000 metres it has a really bad flat spot from idle to 1/3 throttle. if i close the throttle quickly from wide open i get a loud pop or backfire,during deceleration it pops very badly through the exhaust and this decreases as altitude decreases

 

So you have a flat spot from idle to 1/3 throttle?... run it with out the air box door under the exact same conditions when you were experiencing the flat spot...If it's better you are indeed rich and require a leaner needle... OCEMP

 

If it feels better at WOT with airbox door removed , same deal, go to the next size down main jet ...

 

Turn your fuel screw out 1/8th turn to help reduce the popping if it is annoying you, keep in mind popping on decel is normal on a correctly tuned pilot circuit..

 

I would still like to have a look at the left hand side of the carb.....

here is the carb. i understand that some popping is normal but this popping is far from normal. it shoots a blue flame out of the exhaust. i'll try it with the airbox door off and get back to you

IMG_2950.JPG

So you have a flat spot from idle to 1/3 throttle?... run it with out the air box door under the exact same conditions when you were experiencing the flat spot...If it's better you are indeed rich and require a leaner needle... OCEMP

 

If it feels better at WOT with airbox door removed , same deal, go to the next size down main jet ...

 

Turn your fuel screw out 1/8th turn to help reduce the popping if it is annoying you, keep in mind popping on decel is normal on a correctly tuned pilot circuit..

 

I would still like to have a look at the left hand side of the carb.....

i tried it with the airbox door off and it had less power through out the rev range but i am not convinced this is a good way to check a rich or lean condition as i feel the venturi/air speed velocity would be lost due to such a large opening. i reduced the fuel mixture screw from 2.5 turns to 1.5 turns and it helped with the popping and flat spot. i found the biggest improvement to reduce popping was to turn the idle up slightly,maybe i had it too low to begin with. how much does air temperature and humidity play a part when jetting, i'm in the tropics here so its hot and humid. some days my bike runs great some days its terrible,can't work it out,i thought maybe bad fuel or humid days ,i would be interested to hear peoples thoughts

The higher the humidity the richer your bike runs

The higher the humidity the richer your bike runs

the humidity here is between 85 and 90 percent with occasional days higher. air temperature in the mountains is about 30 degrees celsius. 

What needle do you have in the carb?

i have the EMN needle set at the 3rd clip. the needle that came out of it is OBDVS.  is that the standard wr400 needle?

I would try a 150mj and then confirm your pilot circuit( check the FAQ's)

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