new SmartCarb SC3 34mm advanced metering rod carb option

[Chuck78]

Chuck - Thanks for the tip on the YZ250X petcock, I just ordered one. Not sure if mine is stock or not.

Nate - I'll get some different angle photos when I get a chance. If I set the carb level the petcock is pointing directly at the choke knob, I angled it down but now the adjuster wheel is impossible to turn because the throttle cable is pushed into it by the fuel tank. I was going to try angling it the other way but I'll use the Yamaha petcock instead. I hope that solves it because otherwise I'm loving the carb.

Here's the 2016-2022 YZ250X / 1990's 2-stroke WR250Z petcock on a 95-06, straight down outlet.



and here's one of the WR250/450 4-stroke petcocks, I believe a more recent model year? Similar to the YZ250X 2016 but horizontal outlet (& I'm not sure exactly what year this is or what model but it hangs down lower than the 2004 WR250F version some have used), several different WR part #'s over the years, but they appear generally the same, early 2000's is cheaper and I'm pretty certain is the one that definitely fits the KDX220/200H tank bolt spacing, most probably do though):



Keep in mind, the E-Series center spine frame tanks hang down much lower on the sides vs the carb. If the YZ250X petcock doesn't work for your E-Series, I need another one for one of my KDX220 tanks, let me know and I'll buy it off of you.

One other thing to note is that the YZ250X petcock does appear to sit very tight up to the tank... Vs the pictured version of the 4-stroke 2000's WR side outlet appears to hang a little bit lower, the body being a little bit longer.

[Chuck78]

I finally installed mine on Saturday and although I still need to dial it in a little, it runs amazing and smooth with great power delivery. I'm happy with the purchase but the fitment has been tricky at best on my 1990. Look where the choke knob sits...


PXL_20260530_180540113 by The Real Guy Photography, on Flickr

2004 WR250F petcock, I wonder if this is any shorter height than the one you have?

YAMAHA OEM FUEL COCK | 2GU-24500-02-00

https://www.partzilla.com/product/yamah ... 4500-02-00

Hopefully that image from partzilla shows up, I just referenced it from their website. Every 5-7 years it seems that the WR petcock part number changed although they all look pretty darn similar on the 4-stroke versions.

[Chuck78]

Here's the 2005 WR250F version, if the 2004 version is slightly taller, which I can't really determine from the angle of that photo, the 2005 version looks to be hugging tight up to the tank, although it's not 52 or $55, it's $71....

Screenshot_20260602-144453~2.jpg (139.93 KiB) Viewed 3631 times

Double check to make sure it uses the same gasket to the tank, as that will verify that bolt spacing.

Perhaps trying to find some photographs of actual versions of the 2004 petcock, sold on eBay using seller photos instead of stock default photos, might be a good way to tell if the 2004 version is also tight to the tank like this. It could be that the only difference is the reserve pick up tube height.




EDIT - the 2004 WR version part number is also used on the Banshee through 2006, here's a different photo angle, I also saw a used one on eBay that verified it also sits tight to the tank, so if the side outlet is needed, this one is probably the trick then.

Screenshot_20260602-145141~2.jpg (290.89 KiB) Viewed 3631 times

And here's the best photo I could find of the no longer available 1989-1994 KDX200E petcock, granted this is aftermarket, it looks the same as the used ones on eBay that I see that are either missing the fuel nipple that has a habit of falling out (on my H-Series petcicks also !!), or else sitting at a downward 45° facing angle:

Screenshot_20260602-152826~2.jpg (239.76 KiB) Viewed 3622 times

So I think that the WR250F 2004 petcock would likely be the best one, maybe we can get you to get one of those on your bike as a test fitter to see if that added clearance keeps the fuel line up high enough above the choke knob?
I can ship one to you if that '16-'22 YZ250X downward facing outlet doesn't work, if you want to ship me the X version once determined.

Sorry to chime in later after the fact of you ordering the 250X petcock, but that one may work out also.

The 2004 WR250F petcock appears to be the best to use both for the E-Series as well as KX125/KDX hybrids, where the 2016 YZ250X seems to be the best to use for the KDX200H/220 tanks.]

[tosaw]

Wow, thanks for all the info! If the one I ordered doesn't work out we'll go from there.

[SpruceItUp]

Hi everyone. I know a lot of you have been waiting on my review of the SC34. Unfortunately life has been extremely busy since I got back from my trip up North with the KDX and I have not really had any time to do anything. Even the bikes have been covered in mud since I got back. They're finally clean as of today.

I'll be honest, I don't have anything negative to say about the SC34 or the team at SmartCarb. It has been a great carburetor so far. It idles amazingly, off throttle performance is great, low end seems better than it was with my Keihin and so on. It has plenty if power with it. It's easy to get dialed in, just by using the knob on top of the carburetor. Fuel milage seems amazing. I went close to 40 miles of riding up in Wellesville Ohio (according to the speedo/odometer on my other bike) and it seemed like it only used a bit over a gallon of fuel from my tank. Maybe a gallon and a half. I don't have exact numbers, that's just eyeballing it, but it used significantly less than the Keihin does. This was slow moving stuff for the most part, though. Not a whole lot of wide open stuff there. So I'm unsure how it would do on gas if you're riding a lot harder on the gas.
The only problems I had were fitment, and now that Nathan worked with me to get that fixed, it has been great.

I'm unsure if the petcock valve in my bike is stock, it seems like it is, but I have not has any issues related to fitment with it and the carburetor. My petcock actually swivels (the part the hose attaches to does) so I can adjust where the hose goes in relation to the carburetor.

If you have any questions please ask, I have taken much too long to post a review and would love to answer any questions you might have as I may not have touched every basis here.

And thanks to Nathan and the rest of the team at SmartCarb, as they have been extremely helpful.

[Chuck78]

I'm unsure if the petcock valve in my bike is stock, it seems like it is.

My petcock actually swivels (the part the hose attaches to does) so I can adjust where the hose goes in relation to the carburetor.

Ahhh... The old swiveling fuel nipple petcock outlet!
This certainly does in fact sound like an OEM Kawasaki petcock, and not for good reasons! That is supposed to be a pressed fit. I learned that the swiveling means it's worn out, by learning the hard way when I couldn't figure out why my boot was covered in gasoline after I had been smelling gas for a little while on the trail. I thought it was a loose fuel line that was poor fitting, so I tried to twist some bailing wire around it with some pliers as a clamp, and the whole nipple came out the back! I jammed it back in there as best as possible, but luckily we were almost at the end of a multi-day trip when that happened 5 hours from home.

Then I got online after I got back from that trip and found other people complaining of the same issue that there is no longer was a press fit and did not fit tightly.

This is literally just a metal to metal press fit, and all cast metal, nothing machined as best as I can tell, which really surprises me that it even fits good enough to seal for 20 years before becoming problematic....

There is no o-ring or packing seal, and nothing to lock it in place both in swivel orientation and just to hold it in place into the petcock. On top of that, it is just a press fit on two different cast the zinc-aluminum pot metal parts, not even a machined smooth precision fit. It amazes me that this was able to seal for so long before problems.

I repaired that one with JB Weld which has to be allowed to cure fully before seeing fuel, cleaning it and gluing it in place as well as a lot of JB Weld on the exterior, but I have not used that petcock in ages since I discovered the Yamaha WR250Z / YZ250X / YZ125X '22& earlier petcock with the downward facing outlet and the four-stroke WR250 & ATV version of that with the horizontal outlet. Although I did have the fuel nipple on one of those come loose as well, but at least that was a machined press fit into the petcock body with a steel tube. That made me realize I really should be putting a bead of JB Weld or similar around the nipples on any of the petcocks.
The Yamaha petcocks are much better quality overall and very low profile compared to the KDX which is a massively tall tower on the '95-'06, with a very problematic fuel nipple design on all years.

[SpruceItUp]

Ahhh... The old swiveling fuel nipple petcock outlet!
This certainly does in fact sound like an OEM Kawasaki petcock, and not for good reasons! That is supposed to be a pressed fit. I learned that the swiveling means it's worn out, by learning the hard way when I couldn't figure out why my boot was covered in gasoline after I had been smelling gas for a little while on the trail. I thought it was a loose fuel line that was poor fitting, so I tried to twist some bailing wire around it with some pliers as a clamp, and the whole nipple came out the back! I jammed it back in there as best as possible, but luckily we were almost at the end of a multi-day trip when that happened 5 hours from home.

I did not know that! Funny thing is it seals perfectly and has for as long as I've had it.
To be safe I'll just buy a Yamaha petcock as you mentioned. Better safe than sorry.
Thanks!

[Tokyotim]

I am not super active here but I picked up a SC3 from Nathan as they are local to me. I will be making some videos of it next week after it’s installed. I am more active on the 3 big KDX Facebook groups you can search Tee Wall and my name will come up. I will try to remember to post some videos here as well. I put them on Facebook and YouTube

[springstever]

I finally got a chance to put my carb on, take a few pictures, and give her a rip. First, I noticed I had to carefully modify my intake boot by cutting off the tab that is meant to align with the old carb. No big deal there. It is a tight fit if you want it vertical as can be. I found that my throttle cable rubber boot is against the adjusting knob, making it hard to adjust the knob. I have to pull the boot up to adjust the knob. Again, not a big deal. I have to use a lot of fuel line to add the filter, and it makes it hard not to have a big loop sticking out, just asking to be grabbed by a branch or boot buckle. That said, I should get a lower-profile petcock valve that everyone is discussing to help with that issue. Do I really need the filter?

The bike fired right up with the choke on. I tried first without it, but it wanted to be choked. I followed the directions provided. I noticed a huge improvement from my old, worn-out carb. I started with a new plug so I could read it later. Instructions say it needs a short break-in before you try adjusting. It idled great at first. After a two-hour ride, it wouldn't want to idle when warm. It would idle real low until it stalled, indicating that I am too rich. It seemed a little fat, too. Is this by design, Nathan? It definitely had more power and ran way better than what I had going on with the old carb.

I am currently 8 clicks left of factory settings (lean). I rode last night, and it's still too rich, won't idle. I will keep adjusting via the knob, which is really hard to do because of the lack of room up there. Maybe I need to turn more clicks at a time, but I wanted to start with small adjustments. When I pulled the plug, it looked a little rich. Sorry, no pic, I forgot. Any advice on how many clicks I should do at a time, Nathan?

So far, I am liking the upgrade. I will report back after I try dialing in my idle. The instructions say to use the clicker first, so I won't touch the idle screw until I have no other option. I figure I just need to find the sweet spot with the clicker first.

I tried adding pictures, but couldn't figure out how. I tried copy/cut/paste and the Insert Image button in the top menu bar, with no luck. Any advice there?

Cheers, Steve

[tosaw]

Steve I am also 8 clicks leaner and my idle is still very low on my 1990, but it doesn't feel too lean, in fact it may be a tad rich still but man, it pulls strong! I was also going to consult Nathan about it but I may try another click or two.

I installed the YZ250 petcock this weekend and it totally solved my clearance issues. I tried to take a better before picture:

[Chuck78]

Great to hear!
Do you have a picture with the yz250x petcock on it? I have a feeling the 2004 wr250f petcock might still fit better, it would fit like the E-Series petcock on it but much tighter to the tank so the hose will be above the choke knob, I would think it would lend to better fuel hose routing.
If I were you, I would also consult Nathan on how necessary it is to run the supplied fuel filter with their carburetor. The petcocks, at least when new, do you have fully functional filter screens, but that filter included likely is a much finer filtration rate.

I would definitely consult Nathan on tune, as I don't believe they had a 200H on the dyno at all, I do know they field tested at 220, & the dyno mule bike they had was a 200H. All three have different porting, and the 200E has more initial ignition advance, but they all three are somewhat similar in configuration. Obviously the 220 has the lowest port timing for the most torque.

I'm excited to get out to my garage for a little bit tonight but the first time in a while, as I have to get my friend's xr250r engine rebuild put back together with a fresh cylinder, and then I can use a night or two a week to work on my KDX so that I can finally get out and test out the new SmartCarb SC3 34mm! I'm hoping to set up a makeshift log jump learning obstacle out behind my house as well, so I can finally get some double blip techniques mastered. That'll be a good tuning and break in!

[tosaw]

Chuck I didn't take an after picture yet because I need to revamp the feed hose design, as it is there's not enough room to run the external filter but with the brand new petcock screens I'm really not too concerned, my tank is extremely clean and I filter my fuel when I fill the tank.

I have an S shaped feed line from a Honda ATV on order, if that works out I'll include the part number and new photos. I'll try to attach a photo below:

[Nsign]

I found that my throttle cable rubber boot is against the adjusting knob, making it hard to adjust the knob. I have to pull the boot up to adjust the knob. Again, not a big deal. I have to use a lot of fuel line to add the filter, and it makes it hard not to have a big loop sticking out, just asking to be grabbed by a branch or boot buckle. That said, I should get a lower-profile petcock valve that everyone is discussing to help with that issue. Do I really need the filter?

You can tilt the carb up to 15° either side without issue so you may want to play with the tilt just a bit to see if you can get some better clearance between the frame, cable, and clicker.

The filter is included as a courtesy and is recommended, though not required. The gist is to keep your fuel clean going into the carburetor however you do it, whether with just the petcock screen or via adding the in-line filter.

Instructions say it needs a short break-in before you try adjusting. It idled great at first. After a two-hour ride, it wouldn't want to idle when warm. It would idle real low until it stalled, indicating that I am too rich. It seemed a little fat, too. Is this by design, Nathan? It definitely had more power and ran way better than what I had going on with the old carb.

Yes, we tend to set them a bit rich out of the box for two reasons:

1. SmartCarbs have a very tight tolerance between the metering rod and the brass fuel nozzle it rides in. The bars the rods are made from, for example, are precision ground and require no more than a .0003 diameter deviation over their entire 12' length. During the initial break-in period the metering rod laps into the nozzle. They wear in so to speak over that first hour or so. Settle in. This is important because the metering rod is designed to rotate axially about 15°. As the metering rod breaks in the fuel nozzle it becomes more free to rotate. That rotation is crucial for maximum fuel atomization as the rod will "flick" back and forth on its axis at a high frequencies based on intake airflow wrapping around it and engine pulses. The result is finer fuel atomization than even most fuel injectors.
2. And to generally err on the side of caution. Better to be a bit rich than a bit lean.

I am currently 8 clicks left of factory settings (lean). I rode last night, and it's still too rich, won't idle. I will keep adjusting via the knob, which is really hard to do because of the lack of room up there. Maybe I need to turn more clicks at a time, but I wanted to start with small adjustments. When I pulled the plug, it looked a little rich. Sorry, no pic, I forgot. Any advice on how many clicks I should do at a time, Nathan?

Note that each click only moves the metering rod up or down (richer or leaner respectively) just over a thousandth of an inch (.0012). We recommend only adjusting 1-2 clicks at a time and we don't get too hung up on the number you have to go. There are ~150 total clicks in the range of adjustment and you may ultimately go 5-15-25 clicks or more as needed to clean/brighten up the bottom end and bring the idle RPMs up to your liking. Moreover the clicker adjustments really only affect the bottom end and have little effect mid to top so you can go leaner with confidence knowing you're not going to go lean on top. Additionally it's always recommended to assess performance and response while riding, in gear, under load, and with an engine and pipe that are at operating temps. Not on the stand/in neutral and not cold. Lastly when going from richer to leaner there is a bit of a lag in the effect of your clicker adjustments, particularly if you were quite rich to begin with, due to residual fuel in the crank needing cleared out. Best to ride a few minutes between clicks.

If you go too lean on the clicker you start to get softer bottom end response, a bit of hesitation, a bog on quick throttle opening (in gear), and sometimes a bit of a hanging or erratic idle.


Below are the instructions to what we call the Loaded Lean Bog Test. They can help you quickly dial in your SmartCarb after it has been broken in from new (1-2 hours of moderate riding time at or near the as-delivered settings):

1. Ensure the carb is broken in, the engine and pipe are up to temperature, the engine does not have any residual loading up, and you are able to ride in a safe environment.

2. While riding the bike, in 2nd gear, moving about 7-10 miles per hour or jogging speed with zero throttle, lean forward and whack the throttle open quickly from 0 to full open. Do not hold the throttle open or pin the bike for any long period of time. You are simply assessing the off-idle or 0 to 1/4 throttle response in a max load scenario (only as much as you would load the engine during normal riding for a given gear before downshifting). It should pull through and be clean, crisp, and responsive.

3. Using the Clicker, adjust the metering rod lean or counterclockwise 1-2 clicks at a time.

4. Keep performing the test and clicking leaner 1-2 clicks at a time until you find a decided bog when whacking the throttle. That’s what we call the Lean Bog.

5. Once you have found the Lean Bog, use the Clicker to adjust the metering rod rich or clockwise 1 click at a time and repeat the test until the bog goes away and you are left again with crisp, clean, and responsive throttling while performing the test.

6. From there go 1 or 2 clicks richer yet to arrive at a Clicker adjustment or metering rod position for best bottom end performance.

7. Only then do we recommend making fine adjustments to the Idle Set Screw to fine tune your idle RPMs. The Idle Set Screw is very responsive if the metering rod is dialed in to a proper setting using the Clicker. If the rod is off, you may find the Idle Set Screw has little effect on idle RPMs. Lead with the Clicker and follow with small Idle Set Screw adjustments. You may need to repeat the Loaded Lean Bog Test a couple of times as you balance these two settings. (Note that the Idle Set Screw setting should stay between the as-delivered settings and up to 2 full turns in – any adjustment outside of those parameters indicates a non-optimal metering rod setting using the Clicker or some other installation related issue).

8. Once the bottom end is dialed in using the Loaded Lean Bog Test, you can assess the mid to top by feel and plug readings.

[billie_morini]

Nsign, WOW! So much provided detail that reveals the precision for SmartCarbs. Example; "Note that each click only moves the metering rod up or down (richer or leaner respectively) just over a thousandth of an inch (.0012). We recommend only adjusting 1-2 clicks at a time and we don't get too hung up on the number you have to go. There are ~150 total clicks in the range of adjustment and you may ultimately go 5-15-25 clicks or more as needed to clean/brighten up the bottom end and bring the idle RPMs up to your liking."