OK...I'll copy and paste all of the other posts to this thread for it to not take away from the other.
The flatslide isn't an easy fit but it does fit with a bit of modification...I'm running with one....it comes from a 2005(I think) Yami 426cc MX bike....it transforms our bikes into well what a 650 should feel like! I can easily lift the front wheel at any speed in first without clutching it, with clutching at any speed in second......I'm not a wheelie person and do not have the skills to do them at all well. I use the power of the engine to lift the tire maybe a foot off the ground and then either keep it there or let it down asap! Falling off scares the bageebers out of me so I do not hunt for the ballance point.
The carb is a huge improvement but it is not for the faint of heart....it isn't a simple plug and play. I trimmed out the inner portion and rewelded it back in and plated the frame to allow easy installation of this carb, I know of a guy who I copied the settings etc for the carb and he didn't do anything at all to get it to fit....but he struggles hugely getting it in and out whenever he needs to do so. You can buy these carbs of fleabay for anywhere from$200 and up I lucked out and found mine for $178...then spent another $100 on multiple jets and choke plungers to make it the way I needed it to be. Still well worth the cost concidering what it does to our bikes. The other guy had his on a bone stock bike except the carb and a LEXX can, nothing else at all. It was so impressive I went after it with my fully modded engine....and it is the most effective mod performance wise you can do to your bike bar none! The gas mileage does suffer IF you use the carb to it's fullest...lol...It has a pumper on it also....and it does work and work well! If ridden sensibly it has the same size opening as our stock carb so you can get close to the same mileages out of it, but you won't....it is just too much fun to twist that throttle!
FCR-MX 39mm flatslide....search it....
When I was looking at the location this carb needed to be fitted into it is huge for such a small space allowed. You first need a .800" spacer to space the carb away from the top back edge of the starter. It's just that a spacer to go behind the rubber boot on the intake. Then you need to take the lip inside the airbox boot out with a dremel . That lip is there to stop us from sending our stock carbs too far into the airbox boot. The flatslide needs to get further in to be able to fit in this tight space. Now that we have done the basics you need to think about the stuctural space left to deal with. The underside of the frame's back right between the two down tubes is extremely close. Too close for me. Same goes for the righthand side down tube. I took my die grinder and hogged out all of this material....half of the down tube and a quarter of the under side of the main frame. I had a huge area to fit this carb in place and be able to work etc. I thn made new metal pieces to replace the missing parts of the tubes. They basically were formed to allow the carb to fit as if the frame was designed this way. I then welded these new pieces into the frame to close up the tubes once more. I then formed a second skin to help take the strain or stresses that the frame may see in normal use. It was to strengthen the original tube after me forming them. It was a simple job to form and weld new sections over the original tubes. If you didn't know what you were looking for you wouldn't see them.
Now after saying all of that....Greg the guy who did this first didn't do this and still managed to fit this carb. He said it took him hours to take the carb out, slide in a different jet and reinstall the carb.....I just do not have his patience.....if you do then you may be able to deal without modifying the frame.
Again after saying that....I think, if you were to cherry the inside section you wanted to change or crush in you wouldn't need to cut and weld to the extent I did. I'm a welder fitter as well as many other things, so it wasn't that big of a deal to me. After forming the tubes with extreme heat you could always form new skins or layers to be welded as I did to the outside of the modified tubes for strength that is IF you think it's needed to be done in the firstplace....I do if you are asking me.
Would I do it the same way next time, no...I would use heat and crush the tubes where I needed the space, then weld braces as described. It is much faster and less labour intensive. IMHO.
As I have said the new carb is huge compared to the original CV carb although it is only 1/2" longer from entrance to exit so to speak. So it will fit using the stock airbox as well as the .800" spacer. You only have to squeeze .300 of the length into the aibox boot and that is why you need to remove that step that is inside the boot. I will not go in otherwise.
The intake of the carb, on my particular carb as smaller than the airbox boot and had to be increased externally to get up to the airbox boot's inside diameter. I used an old leash soaked in JB Weld and formed a new step so to speak. It worked very well and is very strong. The exit or other end fits perfectly into our stock intake boot. The same size. I have seen different sized airbox ends from different carbs depending upon which bike they came off of. That is a trial and error issue that you will need to deal with depending upon what carb you buy. It doesn't affect the operation of the carb in any way...it has a huge opening to draw air from so it has to be better in a way perhaps.
You will also need to change a few of the jets to get it within the ball park setting so to speak....I have those written down somewhere. I still may need to find tune them a hair but so far it is running well without any fueling issues. You also need to change the needle to a specific one to get the best flow. Again that too is written down. When you get to the stage you need this info I'll post it up for your starting position to work from. It is a very complicated carb to work on jetting wise. Our CV carbs are like comparing the KLR to the GS1200 in technology.....a night and day difference.
I have pics somewhere and will post them once I find them....hope this helps