Anybody running a Smartcarb on their 250/300?

[mog]

The funny part is I read just as many posts about jetting /tuning a smart carb or a lectron than I do a keihin or mikuni ? I'm just saying it's an observation

[Saint728]

I bought a 38mm billet Smartcarb a year ago and it works really well and gets super good gas mileage. I took it off last December when my bike died while riding. I thought it wasn't getting any fuel so when I got home I changed out my Smartcarb for the stock carburetor only to find out it wasn't the problem why I couldn't start my bike. I found out my stator died and I couldn't be bothered with reinstalling my Smartcarb, so it has been sitting in my garage for the past 6 months collecting dust, lol.   

[kingkabong]

I've been running a 38mm cast version since 2014, they are amazing!  I first put it on an old YZ250 and had some trouble, due to some cracks in the old rubber housing on the reed side.  Anyway, once I got that worked out, holy shit!  The bike never ran out of steam, it felt like it would just keep pulling, crazy!  I then put it on a new 2014 KTM250XC.  Not as drastic of a change, but has been very good to me.  I love being able to go a bit leaner or richer depending on the trails, weather, etc.  

A couple things I don't like, the cable retention in the slide... since the cable isn't fully retained in the slide, you can't run any cable slack at all.  Just something you have to get used to, but it's pretty annoying.  And the length, as someone mentioned.  Takes a bit of air box deformation to fit with the stock box on an XC.  I figured out a way to reduce this by pushing from the inside of the air box as you're installing.  You can reduce the amount of bend a bit.  

[bikedude987]

Just got back from 275 miles off Moab offroad, mix of jeep roads, singletrack, and desert, all gnarly.  Running a 38 cast, otherwise bone stock '18 300xc.  Bike ran FLAWLESSLY.  

Tons of power everywhere (more than the Mikuni ever had) and excellent throttle response.  Perfect plug color, little spooge ring on the silencer, and great mileage and power.  

I am EXTREMELY impressed with the carb to say the least.  

That it wasn't peeing gas into the streams when I dumped it or when I had the bike stood straight up in a hole was a great feature to boot! 

Had to tweak the low idle response to get good road cruising for when we were connecting trails, but that was super easy since it's all externally adjustable.  Try THAT with a Lectron! Haha!

 

 

[signal15]

Just got back from 275 miles off Moab offroad, mix of jeep roads, singletrack, and desert, all gnarly.  Running a 38 cast, otherwise bone stock '18 300xc.  Bike ran FLAWLESSLY.  
Tons of power everywhere (more than the Mikuni ever had) and excellent throttle response.  Perfect plug color, little spooge ring on the silencer, and great mileage and power.  
I am EXTREMELY impressed with the carb to say the least.  
That it wasn't peeing gas into the streams when I dumped it or when I had the bike stood straight up in a hole was a great feature to boot! 
Had to tweak the low idle response to get good road cruising for when we were connecting trails, but that was super easy since it's all externally adjustable.  Try THAT with a Lectron! Haha!
 
 

I wanna see how you got up that hill.

I also want to go to Moab. My friend owns a place out there.

[bikedude987]

12 hours ago, signal15 said:

I wanna see how you got up that hill.

I also want to go to Moab. My friend owns a place out there.

Haha, I didn't...could have made it if it were dry, but with a 12" blind hole right before that BIG up....

Seriously, make it happen...ride all the things!

[seer]

On Wednesday, May 02, 2018 at 3:43 PM, mog said:

Don't forget they used to run a 39mm on the 125 and it had more low end than any Jap 125 with a 36 or 38

Awesome lowend for a 125 UNLESS you rolled on past half throttle at low rpm.  Then it was boggggggggggg! I really wanted to try a 36mm on it. 

 

 Mine really opened my eyes to a small bore for offroad riding. 

[signal15]

You guys are making me want to buy one of these...

[bikedude987]

They just ran a 36 on a brandy new yz125 in the dyno room. Started with the Mik, then SmartCarb, the back to the Mik at the end of the day to make sure the baseline hadn't changed.

Short story:  The smartcarb made about 17% more hp in the midrange and almost 4 hp more at peak.  

 

Edited May 10, 2018 by bikedude987

[William1]

For two carbs of same bore size to make different outputs tells me the jetting on one is off. It is simply not physically possible for there to be a difference if both are setup optimally. It is just air and fuel. No extra air, no extra fuel (which it required to vary power). It is possible for one design to provide a better A/F at the various transition points and thereby run smoother. But that is it.

Always be leery when the seller is the one providing the data.

[bikedude987]

3 hours ago, William1 said:

For two carbs of same bore size to make different outputs tells me the jetting on one is off. It is simply not physically possible for there to be a difference if both are setup optimally. It is just air and fuel. No extra air, no extra fuel (which it required to vary power). It is possible for one design to provide a better A/F at the various transition points and thereby run smoother. But that is it.

Always be leery when the seller is the one providing the data.

Seriously, ride one, then make up your mind.

There is much more to it than add fuel and air - get power.  If you have one big fuel droplet and try to burn it you get squat-diddly.  Now fully evaporate that same amount of fuel and you have a high explosive.  

To say two similarly sized carbs are equivalent is simply ignorant.  I would, however, love to see A/F traces for the above runs.

Edited May 10, 2018 by bikedude987

[William1]

4 minutes ago, bikedude987 said:

Seriously, ride one, then make up your mind.

There is much more to it than add fuel and air - get power.  If you have one big fuel droplet and try to burn it you get squat-diddly.  Now fully evaporate that same amount of fuel and you have a high explosive.  

To say two similarly sized carbs are equivalent is simply ignorant.  I would, however, love to see A/F traces for the above runs.

I am far from ignorant when it comes to engines. Neither carb has any magic regarding fuel atomization. Just a needle in a tube. In the write up, they even state the stock carb jetting was calculated and not tested for best performance (credit for the honesty).

[bikedude987]

5 minutes ago, William1 said:

I am far from ignorant when it comes to engines. Neither carb has any magic regarding fuel atomization. Just a needle in a tube. In the write up, they even state the stock carb jetting was calculated and not tested for best performance (credit for the honesty).

I think the article may be a little misleading in how they tested, they later say they used the same incremental method, which I think means multiple runs jetting for max power.

As for the equivalency of a round needle, round throat Mikuni to a metering rod, pressurized fuel supply, variable venturi SmarCarb - I think you're drastically ovesimplifying the matter.  As someone who has ridden bikes that were well jetted on a stock carb (38 Mik, clean plug, little spooge) back to back with a Smartcarb on the same bike - I believe every word and every claim they make.  The difference really is that drastic.

But to each their own opinion. Without seeing irrefutable, clearly presented scientific evidence, we have to trust the experience of others and the assertions of the manufacturer.  

 

[mog]

The difference between a mikuni (hated by many owners ) and a keihin is max of 1hp , the mikuni actually had a tiny bit more peak hp but lost in the midrange to the keihin , the keihin has much more power at half and quarter throttle

4 hp on any carb on any bike is pure fantasy

My 150 sx from lean STD jetting to these mods

Vr4
FMF factory fatty
Keihin carb
Stic

240 Dyno runs and it still doesn't gain 4 hp

James Dean tested tons of carbs and not one had a difference of more than 1hp on a 300

[mog]

They just ran a 36 on a brandy new yz125 in the dyno room. Started with the Mik, then SmartCarb, the back to the Mik at the end of the day to make sure the baseline hadn't changed.
Short story:  The smartcarb made about 17% more hp in the midrange and almost 4 hp more at peak.  
 

Lol look at the graph it even has huge gains at low revs ,did they put a turbo on it ?

Awesome lowend for a 125 UNLESS you rolled on past half throttle at low rpm.  Then it was boggggggggggg! I really wanted to try a 36mm on it. 
 
 Mine really opened my eyes to a small bore for offroad riding. 

Mine had zero bog no matter what you did

[seer]

2 hours ago, mog said:

Lol look at the graph it even has huge gains at low revs ,did they put a turbo on it ?Mine had zero bog no matter what you did

Idle to WOT in an instant with no clutch? Id bet i could do that but not without overly rich needle and main settings. 

[mog]

Most 2 strokes when jetted well can pull top gear on Dyno full throttle at 4000rpm ,tickover is 2000rpm , I guess it depends on what you expect ,to me that's enough ? That's not with rich circuits ,that's with circuits for max hp

[bikedude987]

What can I say, Haters Gonna Hate....

Go ride one, then decide for yourself.

[highmarker]

1st used in a 1929 Chevrolet 6 cyl  

[mog]

What can I say, Haters Gonna Hate....

Go ride one, then decide for yourself.

I've never seen in 30 years anything close to a 4 hp gain from one part on a 125 , it's bs and we all know it