What do I have here?(ATV/4-Wheeler)!?

I cant seem to find what this part is called. Can anyone point me in the right direction? I must be misinterpereting the parts catalog or something? I dont see it in the rear axle section. I think it may be in the rear brake assembly section? click link to view picture.
 
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My friends KQ 300 starts fine and runs, as soon as you put it in gear and try to accelerate its bucks and farts like crazy, not moving... I cleaned carb and it worked good for 1 day... now back to same problem.... could it be such as a bent valve????

Hi Guys!

New member and could really use your advice. I would have to believe this has been an issue for others but a search here came up with nothing......? (Probably me not doing search correctly)
 
I have an 87 Big Bear 350 YFM350FWT
The OEM Mikuni BTM carb is shot and would rather replace than rebuild.
It is no longer made and I have had good luck with NICHE carbs so I ordered a #K-CRB-0006 This was what they said was replacement when ordered. This Carb only uses 1 Throttle cable. The Slide is linked so it uses one. (OEM had 2nd cable coming through top to move slide)
 
Problem is when I ordered a replacement Cable from NICHE (#C-CBL-0061) the Cable wire is a little short, not allowing Throttle to return all the way down to Idle position. I called NICHE and they are at a loss. Haven't gotten back to me after 2+ weeks.
 
What would you recommend other than a carb rebuild?
Can I just use 1 of the OEM cables (It is the right length) and snip/disconnect the other that went to top of Carb for Slide?
Or ??
 
Thanks in advance for any advice you have!!
 
Dave

Bucking started about a month ago and works ok after 1/2 hour warmup.  Today while working on it i discovered that if i put the ignition switch in LIGHT position it runs fine right from the start.
I'm stumped!  Any idea why this could be?  

If you had to choose one mod that you couldn't live without, or had to recommend one what would it be?