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fcr39mx dissapointment

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hi i am very disaponted with the fcr39mx i have a drz400sm BB kit full FMF. my problem is that yesterday night i have set the FCR39mx and the bike was really pulling hard with a lot of throttle response and it was pulling power wheelie in second gear and the temperature was 22 degrees celsius and this morning i went to work with the drz and the bike was ok but this afternoon it was sunny and the temperature is 28 degrees celsius and the bike was running like crap with no power like yesterday night and i tried to close the 1/4 the fuel screw but it doesn`t make a lot of difference i am very desperate caus i am always setting the carb. i have bought the carb 2nd hand from ebay and i have spent abought 350euros to refurbished it gaskets seals needles etc etc but i am fed up of wasting money on this carb i dont know what is the problem. i think i will buy the mikuni TM40 for the drz can anyone help me with some advice on the fcr and the mikuni TM40 please?

thanks

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I'd love to help but I think you should post this in the technical section. I'm sure someone on here could find this thresd and help but I think you'd be waiting a while. So go ahead and put it under the dirt bike technical forum.

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Another case of 'you get what you pay for'.

 

Once set, you do not have to keep fiddling with it.

The fuel screw is for idle ONLY

No doubt, the carb you bought was someone elses nightmare.

I am pretty sure your issues stem from having taken the carb body apart. As I've said to you before, very few people can properly put one back together.

 

Very few people run the Mikuni as the FCR works better. You just need a good FCR and not one with problems

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yesterday night i have set the FCR39mx and the bike was really pulling hard with a lot of throttle response and it was pulling power wheelie in second gear and the temperature was 22 degrees celsius and this morning i went to work with the drz and the bike was ok but this afternoon it was sunny and the temperature is 28 degrees celsius and the bike was running like crap with no power like yesterday

 

6°C do not make any relevant difference, imho jetting is not your problem.

there can be a difference only if you start from a really rich condition at22°C that become unusable rich at 28°C.

can you list your complete jetting?

Edited by 30x26
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Something is not right, my FCR-MX runs between 40-100 F temps and between 150-5000 feet with little noticeable effect.   If anything effects of elevation are more noticeable than temps. 

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But i have put in all new gaskets and o rings new what else could be wrong with the carb i have changed every little piece in it abd still does not hold the setting i am afraid to buy another fcr carb. Is the mikuni tm40 a low level carb or it runs good like the fcr? When i set the fcr good it pulls alot hard like a dream but the day after it doesnt pull the same and i hate that. I cannot understand why

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 I cannot understand why

 

Not trying to be rude here but "used FCR from another bike" should be enough explanation.  Some have made a used FCR work great, more have had problems like you which is why there is not a lot of people in this forum suggesting the used route unless you get a screaming deal and can afford to throw it away when/if it can't be made to work properly.  

 

It does look like the TM 40 is popular for the DR 650's but I don't see much about them used on the DRZ

Edited by npm

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but i think it will work with the drz434 just need to be jetted correctly and maybe someday i will but a new fcr39mx from tumpertalk but for now i will try the mikuni TM40

thanks for helping.

i will not ever buy a used carb cause it costs me abought 600 euros like a new one and it still has problems

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If the bike ran great the night before then there is no reason it cannot be made to run the same the next day. Are you certain that your perspective did not change, cause jetting with a 6C difference could not make all that difference, great-to-crap.

 

Check all hoses, vac lines, boot connections, etc.

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But i have put in all new gaskets and o rings new what else could be wrong with the carb i have changed every little piece in it abd still does not hold the setting i am afraid to buy another fcr carb. Is the mikuni tm40 a low level carb or it runs good like the fcr? When i set the fcr good it pulls alot hard like a dream but the day after it doesnt pull the same and i hate that. I cannot understand why

As many people have told you, you bought a used carb. Then you took apart something that was not designed to take apart.

 

If you take a person, remove their brain, then put it back in, it is highly doubtful that person will function properly.

 

Your carb is not 'changing setting', the internal seals that you think you replaced are not working properly. This why only a real expert has a good chance of taking an FCR body apart and reassembling. I will assume the body itself (where the slide wheels ride on) is not worn down either.

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my jetting is as eddie recomend at sealevel  45pj  emn needle 160mj 100paj 200maj R & D fuel screw 2 1/4 turns out

 

with BB and sm cams imho it's rich everywhere, it could be extremely rich when temperature goes up.

retry the bike a few times at  low temperature, if it always works fine it's a jetting problem

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at lower temperature the bike runs better. can you tell me why with the big bore the bike runs richer cause since i have installed the bigbore even the engine sound is different.

my jetting is 160 main EMN 3rd clip 45 pilot jet 2 1/4 fuel screw. so what you suggest for jetting can i try the needle on the 2nd clip?

thanks for helping me

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As many people have told you, you bought a used carb. Then you took apart something that was not designed to take apart.

 

If you take a person, remove their brain, then put it back in, it is highly doubtful that person will function properly.

 

Your carb is not 'changing setting', the internal seals that you think you replaced are not working properly. This why only a real expert has a good chance of taking an FCR body apart and reassembling. I will assume the body itself (where the slide wheels ride on) is not worn down either.

 

 

no its not worn out. the body of the carb seems  to be fine visually

Used carbs are a gamble. 

Edited by 150ron

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at lower temperature the bike runs better. can you tell me why with the big bore the bike runs richer cause since i have installed the bigbore even the engine sound is different.

my jetting is 160 main EMN 3rd clip 45 pilot jet 2 1/4 fuel screw. so what you suggest for jetting can i try the needle on the 2nd clip?

thanks for helping me

 

152.5 , ncyr at 2nd-3rd clip . then test if idle reacts to pilot screw and choose the proper pilot jet (probably smaller than 45) .

do you already have another needle?

Edited by 30x26

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I'd try lowering the needle and a 155 or 158 main . I've used a number of used carbs , try to get off low hour or newer bikes/quads so wear isn't bad(if slide wear is bad, nothing can be done) but with new seals and jetting they work as good as new without the double cost. Just takes knowhow instead of cash. Never split a fcr or dealt with one that was .

Edited by jjktmrider

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