650/X-2 Best carb for 650sx

[waxhead]

A 44-46mm carburetor will perform exceptionally well if paired with a properly designed manifold. However, if the manifold features oversized runners, as is sometimes used, performance may suffer due to reduced air velocity.

 

[Micc]

I have a SBN44 on my 650SX with a factory pipe, starts great, runs great, idles great.

 

[Storbeck]

A 44-46mm carburetor will perform exceptionally well if paired with a properly designed manifold. However, if the manifold features oversized runners, as is sometimes used, performance may suffer due to reduced air velocity.

I have never done the test but always suspected that the factory manifold with an adapter is probably better than the aftermarket manifolds that have bigger volume.

I'm more of a dual carb guy so not sure if I'll ever get around to doing that test.

 

[WFO Speedracer]

I have run 44's on every 650 I have ever had in a standup , they always start and run great and the jetting is pretty well known , unless you don't jet it properly it's really hard to go wrong with one.

Most of the time I use a stock intake with an adaptor and it works great. you just need to sand the inside of the intake a bit with a sanding drum to match the adaptor. I have never run one back to back with an adaptor versus a 44 intake manifold but IMHO the intake just holds the carb on the engine.

 

[Storbeck]

What's this about a 440 intake? How does that work?

 

[WFO Speedracer]

I have no idea how that got there , I must of fat fingered it, but I fix it

 

[Storbeck]

Ah, I'm stupid, that was genuinely not meant to be a wise -a** comment I know you're an outside of the box old school guy so figured maybe there was some trick that I hadn't heard of that uses a js440 intake but completely couldn't picture how that might work lol.

 

[WFO Speedracer]

Ah, I'm stupid, that was genuinely not meant to be a wise -a** comment I know you're an outside of the box old school guy so figured maybe there was some trick that I hadn't heard of that uses a js440 intake but completely couldn't picture how that might work lol.

I am old school , I think I started at the Kawi dealership in 1986 , I was 23 years old when I rode my first standup , I worked at the Honda dealership for 4 years before that , but I also like to keep things simple , to me a 44 adaptor plate is simple , effective and it works well on both 650's and 750's.

 

[waxhead]

I have run 44's on every 650 I have ever had in a standup , they always start and run great and the jetting is pretty well known , unless you don't jet it properly it's really hard to go wrong with one.

Most of the time I use a stock intake with an adaptor and it works great. you just need to sand the inside of the intake a bit with a sanding drum to match the adaptor. I have never run one back to back with an adaptor versus a 44 intake manifold but IMHO the intake just holds the carb on the engine.

Watch this space for the new Wax Racing HV "High Velocity" series of manifolds! Unlike others on the market that act more like simple adapters, our HV manifolds are engineered to be true performance pieces. These aren’t just fillers—they’re built to maximize airflow speed, enhancing the power and efficiency of your engine. Most companies focus on adapting fitment, but we’ve designed the HV series to actually improve your ride by keeping that air-fuel mixture moving fast, getting more punch where you need it.

 

[kevbo]

A stock 1991-1996 carb and intake flows enough for stock ported 650s. Any carb mod beyond that should be a pair of SBN44s. Any of the Keihins work great if you can find a manifold. Oversized singles tend to burn pistons during long full throttle runs.

 

[Mobile Chernobyl]

I am old school , I think I started at the Kawi dealership in 1986 , I was 23 years old when I rode my first standup , I worked at the Honda dealership for 4 years before that , but I also like to keep things simple , to me a 44 adaptor plate is simple , effective and it works well on both 650's and 750's.

Have done this same mod (RCJS SBN44 adapter or similar) to a few friends skis and it just transforms the ski from an unreliable turd to a reliable donkey. Nothing fancy, but at least the ski is now gonna run every time and pick up a little top end maybe. I did more 650SX riding this summer than I ever had thanks to my buddy hauling his around the southwest on our trips.

 

[WFO Speedracer]

I had a customer that fought with a 650SX and a 38 Kehin for a few years, it kept running richer and richer , I told hit to stop jacking with it and oput a 44 Mikuni on it, he texted me asking why he waited so long, the ski ran so much better than it ever had since he owned it.

 

[kevbo]

All Keihin CDK-CDK2 carbs have an O-ring on the needle valve body that always dries up. All carbs that have been used for a few years will need this O-ring replaced even if everything else is perfect. I have found common metric O-rings to be a little fat but will go in with some lube.

 

[E350]

^^^ Wait just one minute! Is that why my Keihin CDK2 carb leaked a pint of fuel into the crankcase in the 550sx during a Summer of non-use?

 

[waxhead]

A stock 1991-1996 carb and intake flows enough for stock ported 650s. Any carb mod beyond that should be a pair of SBN44s. Any of the Keihins work great if you can find a manifold. Oversized singles tend to burn pistons during long full throttle runs.

I agree that acceleration is one of the most enjoyable parts of riding, and I'm a big advocate for dual carb setups as well—after all, you’ve got to fuel the power, right? A 46mm carb on a 650 engine is an excellent upgrade that significantly boosts acceleration compared to the stock carb. It’s a strong middle ground between the stock carb and the full power of duals. Of course, working with twin carbs on an X2 can be a serious hassle; it’s a challenge to fit and maintain,

 

[Storbeck]

Something tells me wax would run dual 48's...

 

[waxhead]

Something tells me wax would run dual 48's...

Oh, absolutely! He’d go for reverse jetting on those duals without a second thought—it’s like giving the carbs a little attitude adjustment. But hey, not everyone’s ready to roll up their sleeves and dive into that level of tuning. Some people just want to keep it simple, but where’s the fun in that, right?

 

[WFO Speedracer]

Oh, absolutely! He’d go for reverse jetting on those duals without a second thought—it’s like giving the carbs a little attitude adjustment. But hey, not everyone’s ready to roll up their sleeves and dive into that level of tuning. Some people just want to keep it simple, but where’s the fun in that, right?

The fun in that is that wile everyone else is on the beach with their hoods up and their carbs apart tuning I am out riding, their is something to be said for that.