Reddit mentions of Innovate Motorsports (3844) MTX-L Wideband Air/Fuel Ratio Gauge Kit, Bosch LSU 4.9 - includes LSU 4.9 Sensor

CV in general, with very rare exceptions.

OK. The way a CV carb works, you have a slide that goes up and down that lets more or less air in. The bottom of this slide has the main jet needle attached, so that as the slide rises more gas comes in via the main jet. You do NOT get to control how that slide rises. At all. You have no control over it. What YOU get to control is a butterfly valve mounted behind it, between the slide and the motor. You whack on that valve and incoming air causes the main slide to rise...with a distinct delay.

The other drawback is you now have two different things in the air path - the slide and the butterfly valve. That limits airflow...which is why you can replace a 38mm factory CV carb on an XS650 for example with a "smaller" Mikuni VM34 and still get a serious power boost.

See diagram - the butterfly valve is listed as the "throttle valve", it's just a round piece of brass on a stick that can be twisted:

http://www.viragoownersclub.org/Dr%20Piston/Images/Hitachi_carb.jpg

So with airflow making the main slide rise, the "quality" of that incoming airflow matters. That airflow has to be carefully directed to make the main slide rise properly. If you look at the intake side of one of these you'll see "extra holes" around the main bore - air has to go in those holes "just so" to make the main slide rise properly.

In this example there's a "bent oval" at the top of the intake bore and a couple more holes just inboard of the hole on the bottom:

http://www.dudeworld.com.au/images/CV3.jpg

For reasons I don't fully understand CV carbs need to feed from a shared "pool" of calmed air called an airbox. I do know that towards the end of the period where the major Japanese makers were using CV carbs in high-performance sportbikes like the GSXRs, Ninjas, etc. they were using airboxes with volumes greater than the gas tank capacity.

And then they finally gave up and went to fuel injection that doesn't need that bullshit...

In a "classic" carb of the roundslide, flatslide or similar design, there's a slide that you yank on directly with a wire attached to the throttle. In these carbs (Mikuni VM/TM, Keihin CR/FCR, etc.) when you call for that slide to rise (with the main jet needle on the bottom) it rises RIGHT NOW, no delay. And they're fully compatible with individual pod filters...well, good quality ones anyhow, there's some bad ones on the market (Chinese Ebay crap, etc.).

The CV carbs were put in mainly for smog control reasons, to avoid having to go to catalytic converters. Which means you have a second set of problems IF you manage to solve the airflow issues: the CV carbs aren't too adjustable and with the serious difference in airflow from the stock air cleaner to the pods, you're going to have to change jets to alter the fuel supply to match the change in airflow from the filter change. And then if you alter the pipes as a lot of bike modders do, you'll have more airflow changes, more messing with the carb(s).

The one advantage to the CV carb is that the main slide won't rise faster than what the engine needs. With some roundslide/flatslide setups you have to learn to hesitate just a bit in the midrange to let the motor catch up to what the carb is doing, especially if you run carbs too big for the motor's state of tune. When I built my XS650 25 years ago or so I bought VM36 carbs that were a tad too big and had to learn to ride it up with the throttle, but I lived with it because the top-end rush was awesome :).

One more thing. There's a new tech available that the bike world hasn't caught up with yet that will tell you THE TRUTH about what your air/fuel mixture is really doing with no guesswork:

http://www.amazon.com/gp/product/B004MDT8MW/ref=s9_simh_gw_p263_d1_i1?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=desktop-5&pf_rd_r=0SR1QZXMS7Y8R9K1FG1T&pf_rd_t=36701&pf_rd_p=1935682402&pf_rd_i=desktop

For less than $200 you can get an air/fuel meter that plugs into the exhaust through a mount you have to add for it. You can then take the sender and gauge out once you have it tuned right and plug the sensor bung with a bolt. This will tell you exactly what the mixture is at any RPM range...you want 14.7:1 air/fuel most of the time, 12.8:1 balls out wide open.

A gauge like this will turn you into a jetting Jedi, but it still won't solve air direction problems on CV carbs with pods.