FCR MX 39 Jetting Recommendation

[Owen Elderkin]

So,  i just got a Thumpertalk FCR kit from a guy and it has everything included plus the extended screw and high choke (brand new condition).  Only thing he changed from what he said was the 160 to a 155 that it came with (i amassuming i'll put 160 back in)  He was running 3x3 with e header and two brothers slip on, i will be running 3x3 and MRD.  Basically wondering what ya'll recommend for my jetting.  Also the kit came with the EMN needle in and am wondering if i will be getting that 1/4 throttle putter i've heard about and what jetting will eliminate that.  Thanks 

 

also if theres any heads up you guys wanna give me before i start thats welcome too as i havent even taken the mikuno off as i'm at work 

Edited July 16, 2020 by Owen Elderkin

[Owen Elderkin]

if the answer is buy the jd kit, i'll do that but i kinda want the answer to what will make it run as proper as possible right now without having that yet

[ohiodrz400sm]

I would put the 160 in and start with the common TT recommendation. 

The bike is extremely tolerant on the main jet.  If it doesn't like the clip or diameter, you'll know by the stutter (lean) or sputtering/ popping and black smoke (rich) when you hold it at that particular throttle opening. Just past cracked is the diameter which is represented by the last letter of the needle.  The closer to Z , the leaner the diameter.  Past "cracked" to 1/4 is the clip height. If you hold it at a particular rpm at 1/4 throttle and it feels as though it is struggling or being held back until you open the throttle just a touch more, than your clip is probably too lean. 

The o-ring mod is mandatory or it will bog on quick throttle movements. A #78 o-ring works best.  Buy a pack as they are only good for a season before they break.

With the carb off the bike, hook a fuel line up and check the squirt strength and timing.  It needs to be as close as possible to the slide without hitting it. Eye ball it the best you can off the bike and then fine tune in the bike an 1/8th turn are a time. Also double check the float height, 9mm is a good starting point.

Just a heads up, the FCR-MX w/S boot setup on the DRZ is the hardest to install correctly of any dirt bike I have encountered in 30 years. It doesn't like to just "pop" in like most bikes.  It seems like it is always trying to squirm out on 1 side or the other. You also cannot see a damn thing on the right side because of the shock.  For me to have a warm and fuzzy, I used to remove the muffler and swing the subframe up.  I would then remove the airboot (and catch tank) from the box and install the airboot onto the carb.  This way, I could see and feel when it was seated fully.  I would then drop the subframe down, pop the boot back on the box, and then fit the carb fully into the engine side. Oh yeah, you have to pry the carb a bit to stretch the airboot to get it fully into the intake.  Tighten the intake while persuading it forwarded. Sounds like a pain in the ass but once you do it a few times it is quick and easy.

Getting the cables, and throttle housing in just the right spot so the throttle snaps closed is also an exercise in patient the 1st few times.  Make sure the tube and assembly are clean and just know that it will work, you just haven't found the happy spot yet. Also, don't forget to verify that the slide is opening 100% before the throttle tube bottoms out. Hold the throttle wide open with your left hand and try to rotate the throttle wheel on the carb counter clockwise with a screw drive or something blunt. Any play there is free horsepower.

[Owen Elderkin]

46 minutes ago, ohiodrz400sm said:

I would put the 160 in and start with the common TT recommendation. 

The bike is extremely tolerant on the main jet.  If it doesn't like the clip or diameter, you'll know by the stutter (lean) or sputtering/ popping and black smoke (rich) when you hold it at that particular throttle opening. Just past cracked is the diameter which is represented by the last letter of the needle.  The closer to Z , the leaner the diameter.  Past "cracked" to 1/4 is the clip height. If you hold it at a particular rpm at 1/4 throttle and it feels as though it is struggling or being held back until you open the throttle just a touch more, than your clip is probably too lean. 

The o-ring mod is mandatory or it will bog on quick throttle movements. A #78 o-ring works best.  Buy a pack as they are only good for a season before they break.

With the carb off the bike, hook a fuel line up and check the squirt strength and timing.  It needs to be as close as possible to the slide without hitting it. Eye ball it the best you can off the bike and then fine tune in the bike an 1/8th turn are a time. Also double check the float height, 9mm is a good starting point.

Just a heads up, the FCR-MX w/S boot setup on the DRZ is the hardest to install correctly of any dirt bike I have encountered in 30 years. It doesn't like to just "pop" in like most bikes.  It seems like it is always trying to squirm out on 1 side or the other. You also cannot see a damn thing on the right side because of the shock.  For me to have a warm and fuzzy, I used to remove the muffler and swing the subframe up.  I would then remove the airboot (and catch tank) from the box and install the airboot onto the carb.  This way, I could see and feel when it was seated fully.  I would then drop the subframe down, pop the boot back on the box, and then fit the carb fully into the engine side. Oh yeah, you have to pry the carb a bit to stretch the airboot to get it fully into the intake.  Tighten the intake while persuading it forwarded. Sounds like a pain in the ass but once you do it a few times it is quick and easy.

Getting the cables, and throttle housing in just the right spot so the throttle snaps closed is also an exercise in patient the 1st few times.  Make sure the tube and assembly are clean and just know that it will work, you just haven't found the happy spot yet. Also, don't forget to verify that the slide is opening 100% before the throttle tube bottoms out. Hold the throttle wide open with your left hand and try to rotate the throttle wheel on the carb counter clockwise with a screw drive or something blunt. Any play there is free horsepower.

kind of overwhelmed before i even start after reading that but thats way more help than i expected to get.  did not know about the o ring mod but just found @William1s instructions so i'll make sure to buy some of those on the way home.  i'm sure as with even the simple things i do to this bike it will turn into a 3 day warzone instead of a 1 hour job lol.  thanks 

Edited July 16, 2020 by Owen Elderkin

[Owen Elderkin]

33 minutes ago, Owen Elderkin said:

kind of overwhelmed before i even start after reading that but thats way more help than i expected to get.  did not know about the o ring mod but just found @William1s instructions so i'll make sure to buy some of those at autozone on the way home.  i'm sure as with even the simple things i do to this bike it will turn into a 3 day warzone instead of a 1 hour job lol.  thanks 

 

Edited July 16, 2020 by Owen Elderkin

[Tony Wyp]

1 hour ago, Owen Elderkin said:

 

How about just putting the carb on and see how the bike runs ?

I think you might have been over-internetting, and scared yourself with imagined problems.

[Owen Elderkin]

1 hour ago, Tony Wyp said:

How about just putting the carb on and see how the bike runs ?

I think you might have been over-internetting, and scared yourself with imagined problems.

? "just put it on"        got it

[MojaveSidecar]

5 hours ago, ohiodrz400sm said:

I would put the 160 in and start with the common TT recommendation. 

The bike is extremely tolerant on the main jet.  If it doesn't like the clip or diameter, you'll know by the stutter (lean) or sputtering/ popping and black smoke (rich) when you hold it at that particular throttle opening. Just past cracked is the diameter which is represented by the last letter of the needle.  The closer to Z , the leaner the diameter.  Past "cracked" to 1/4 is the clip height. If you hold it at a particular rpm at 1/4 throttle and it feels as though it is struggling or being held back until you open the throttle just a touch more, than your clip is probably too lean. 

The o-ring mod is mandatory or it will bog on quick throttle movements. A #78 o-ring works best.  Buy a pack as they are only good for a season before they break.

With the carb off the bike, hook a fuel line up and check the squirt strength and timing.  It needs to be as close as possible to the slide without hitting it. Eye ball it the best you can off the bike and then fine tune in the bike an 1/8th turn are a time. Also double check the float height, 9mm is a good starting point.

Just a heads up, the FCR-MX w/S boot setup on the DRZ is the hardest to install correctly of any dirt bike I have encountered in 30 years. It doesn't like to just "pop" in like most bikes.  It seems like it is always trying to squirm out on 1 side or the other. You also cannot see a damn thing on the right side because of the shock.  For me to have a warm and fuzzy, I used to remove the muffler and swing the subframe up.  I would then remove the airboot (and catch tank) from the box and install the airboot onto the carb.  This way, I could see and feel when it was seated fully.  I would then drop the subframe down, pop the boot back on the box, and then fit the carb fully into the engine side. Oh yeah, you have to pry the carb a bit to stretch the airboot to get it fully into the intake.  Tighten the intake while persuading it forwarded. Sounds like a pain in the ass but once you do it a few times it is quick and easy.

Getting the cables, and throttle housing in just the right spot so the throttle snaps closed is also an exercise in patient the 1st few times.  Make sure the tube and assembly are clean and just know that it will work, you just haven't found the happy spot yet. Also, don't forget to verify that the slide is opening 100% before the throttle tube bottoms out. Hold the throttle wide open with your left hand and try to rotate the throttle wheel on the carb counter clockwise with a screw drive or something blunt. Any play there is free horsepower.

Hi Ohio

Yours is the best explanation I have seen on manually tuning an FCR carb.  Is there a document somewhere for the TT recommendations?  I didnt see anything as comprehensive as your explanation in the FAQ.

Here is a link to a video I found about how an FCR works and how to tune it, but he is using a air/fuel meter.

Randy from Wrightwood

[ohiodrz400sm]

1 hour ago, MojaveSidecar said:

Hi Ohio

Yours is the best explanation I have seen on manually tuning an FCR carb.  Is there a document somewhere for the TT recommendations?  I didnt see anything as comprehensive as your explanation in the FAQ.

Here is a link to a video I found about how an FCR works and how to tune it, but he is using a air/fuel meter.

Randy from Wrightwood

William 1 has the best pilot /fuel screw setting how too I've ever seen. It's worth a look if you haven't read it already.

The FCR-MX setting are in the FAQs.  Also Google search will find 100k threads.  Basically 160 main, EMN needle 3rd clip, 45 pilot, 100 paj, 200 Maj.

Like I said, ap timing, needle diameter and height are painfully obviously when the bike isn't happy.    The bike is extremely tolerant on the main and needle taper.  I have literally gone from a 145 to 170 in a single day, and the bike hardly noticed.  It carbureted cleanly with both, but runs stronger overall, especially in the midrange, when it is on the rich side of things. 1 way to test is by slightly taping off the airbox.  Less air richens the mixture.  If doing this gives the bike better roll on power than go up a few sizes on the main.  You can pretty much do the same thing by running with the choke also.  If wide open feels better with the choke on , go up on the main.

Something else to consider is you can use jetting to adjust the feel of the power, just like the tuners for the EFI MX bikes. A little lean makes the power feel a sharper and quick revving.  A touch rich is smooth and long pulling. Don't be afraid to buy a range of sizes and play around.  The main can be changed quickly with the carb on the bike once you get the feel for it.  What you like best may not be what the next guy thinks is perfect.

[bumtarder]

The TT kit comes with the EMR which I prefer over the EMN due to the leaner R root diameter which the DRZ seems to prefer.I find the EMN needle to be pretty junky in the lower throttle rpms for my liking.

[Owen Elderkin]

12 hours ago, ohiodrz400sm said:

William 1 has the best pilot /fuel screw setting how too I've ever seen. It's worth a look if you haven't read it already.

The FCR-MX setting are in the FAQs.  Also Google search will find 100k threads.  Basically 160 main, EMN needle 3rd clip, 45 pilot, 100 paj, 200 Maj.

Like I said, ap timing, needle diameter and height are painfully obviously when the bike isn't happy.    The bike is extremely tolerant on the main and needle taper.  I have literally gone from a 145 to 170 in a single day, and the bike hardly noticed.  It carbureted cleanly with both, but runs stronger overall, especially in the midrange, when it is on the rich side of things. 1 way to test is by slightly taping off the airbox.  Less air richens the mixture.  If doing this gives the bike better roll on power than go up a few sizes on the main.  You can pretty much do the same thing by running with the choke also.  If wide open feels better with the choke on , go up on the main.

Something else to consider is you can use jetting to adjust the feel of the power, just like the tuners for the EFI MX bikes. A little lean makes the power feel a sharper and quick revving.  A touch rich is smooth and long pulling. Don't be afraid to buy a range of sizes and play around.  The main can be changed quickly with the carb on the bike once you get the feel for it.  What you like best may not be what the next guy thinks is perfect.

definitely hoping i'll figure out not having to pull it back off for main jet swaps.  slept from when i got off work till this morning after getting home at almost 2am picking that carb up the preivious night lol

[Ud_Luz]

I deleted all the OT nonsense. Any more and I'll delete the poster.  

[ohiodrz400sm]

9 minutes ago, Owen Elderkin said:

definitely hoping i'll figure out not having to pull it back off for main jet swaps.  slept from when i got off work till this morning after getting home at almost 2am picking that carb up the preivious night lol

Everything but the leak and air jets can be changed with the carburetor in place.

To change the main all you need is a 17mm wrench, 6mm socket and 1/4 drive ratchet.  It's simple to get out.  What takes practice is being able to blindly find the hole to reinstall.  You'll likely fumble around the 1st few times but you'll get the hang of it.  

The pilot can also be changed without removing by slightly rotating the carb.

Needle is easy as well.  You only need to remove 6 bolts. 2 seat , 2 tank and the 2 shrouds bolts going into the radiators. Pull the tank with the shrouds attached. 

Now that I think about it, I guess technically there are 8 and a set screw.   Once the tank is off you remove the 2 socket head screws for the top of the carb.  Then, twist the throttle to raise the slide to access the set screw that traps the needle.  To get the needle out, quickly snap the throttle wide open with your right hand and "catch" the needle with your left.  Don't worry, it won't going flying out. Only "peek" out enough for you to grab it.

[Owen Elderkin]

3 minutes ago, ohiodrz400sm said:

Everything but the leak and air jets can be changed with the carburetor in place.

To change the main all you need is a 17mm wrench, 6mm socket and 1/4 drive ratchet.  It's simple to get out.  What takes practice is being able to blindly find the hole to reinstall.  You'll likely fumble around the 1st few times but you'll get the hang of it.  

The pilot can also be changed without removing by slightly rotating the carb.

Needle is easy as well.  You only need to remove 6 bolts. 2 seat , 2 tank and the 2 shrouds bolts going into the radiators. Pull the tank with the shrouds attached. 

Now that I think about it, I guess technically there are 8 and a set screw.   Once the tank is off you remove the 2 socket head screws for the top of the carb.  Then, twist the throttle to raise the slide to access the set screw that traps the needle.  To get the needle out, quickly snap the throttle wide open with your right hand and "catch" the needle with your left.  Don't worry, it won't going flying out. Only "peek" out enough for you to grab it.

i hope someones paying you for these responses

[ohiodrz400sm]

9 minutes ago, Owen Elderkin said:

i hope someones paying you for these responses

Don't worry, my employer is paying me right now.  I need distractions to stay motivated, if that makes any sense.

[bumtarder]

That's the beauty of the FCR racing carburetor.Most jetting changes can be done trackside without removing and often without disturbing the carb in any way.A few specialized tools makes it even easier.To change the pilot jet I unbolt and swing the regulator/rectifier out of the way to get my whole hand under the float bowl.A tiny thumb ratchet with the correct bit and 6mm socket make it a snap.

[Owen Elderkin]

On 7/16/2020 at 1:42 PM, ohiodrz400sm said:

I would put the 160 in and start with the common TT recommendation. 

The bike is extremely tolerant on the main jet.  If it doesn't like the clip or diameter, you'll know by the stutter (lean) or sputtering/ popping and black smoke (rich) when you hold it at that particular throttle opening. Just past cracked is the diameter which is represented by the last letter of the needle.  The closer to Z , the leaner the diameter.  Past "cracked" to 1/4 is the clip height. If you hold it at a particular rpm at 1/4 throttle and it feels as though it is struggling or being held back until you open the throttle just a touch more, than your clip is probably too lean. 

The o-ring mod is mandatory or it will bog on quick throttle movements. A #78 o-ring works best.  Buy a pack as they are only good for a season before they break.

With the carb off the bike, hook a fuel line up and check the squirt strength and timing.  It needs to be as close as possible to the slide without hitting it. Eye ball it the best you can off the bike and then fine tune in the bike an 1/8th turn are a time. Also double check the float height, 9mm is a good starting point.

Just a heads up, the FCR-MX w/S boot setup on the DRZ is the hardest to install correctly of any dirt bike I have encountered in 30 years. It doesn't like to just "pop" in like most bikes.  It seems like it is always trying to squirm out on 1 side or the other. You also cannot see a damn thing on the right side because of the shock.  For me to have a warm and fuzzy, I used to remove the muffler and swing the subframe up.  I would then remove the airboot (and catch tank) from the box and install the airboot onto the carb.  This way, I could see and feel when it was seated fully.  I would then drop the subframe down, pop the boot back on the box, and then fit the carb fully into the engine side. Oh yeah, you have to pry the carb a bit to stretch the airboot to get it fully into the intake.  Tighten the intake while persuading it forwarded. Sounds like a pain in the ass but once you do it a few times it is quick and easy.

Getting the cables, and throttle housing in just the right spot so the throttle snaps closed is also an exercise in patient the 1st few times.  Make sure the tube and assembly are clean and just know that it will work, you just haven't found the happy spot yet. Also, don't forget to verify that the slide is opening 100% before the throttle tube bottoms out. Hold the throttle wide open with your left hand and try to rotate the throttle wheel on the carb counter clockwise with a screw drive or something blunt. Any play there is free horsepower.

Hey so what does it mean if I can only start/run the bike while on choke? Basically does immediate after pushing back in. Is that just the fuel screw turns? I set the idle higher already 

[ohiodrz400sm]

25 minutes ago, Owen Elderkin said:

Hey so what does it mean if I can only start/run the bike while on choke? Basically does immediate after pushing back in. Is that just the fuel screw turns? I set the idle higher already 

Only running on choke means the pilot is either plugged or the idle screw setting is too low.

[Owen Elderkin]

7 minutes ago, ohiodrz400sm said:

Only running on choke means the pilot is either plugged or the idle screw setting is too low.

Just turned the idle up super high and it dies when choke pushes in 

Edited July 18, 2020 by Owen Elderkin

[Owen Elderkin]

29 minutes ago, Owen Elderkin said:

Just turned the idle up super high and it dies when choke pushes in 

Prime also doesn’t work