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When I purchased my 86 CB450SC it came with Keihin VB31A carbs on it (no clue why, didn't have the knowledge then, and huge lack of info on these available). I've had popping on decel (clean carbs, no leaks or major ones, decent sync).

I was going to remove my airbox + hbox + add pods + new exhaust on the bike. I figured I would rejet the carbs at the same time instead of before. I can only assume I'm already running a little lean already with the popping so I was going to bump up my main and try a few sizes.

I wanted to get a few new jets to slowly tune this in after the modifications. Does anyone have information on the part number for the fluid needle and slow jet? Maybe I don't need to change the slow jet or fluid needle and I'm confused (I'm very sure my main needs to go up regardless). Here's the info I do have:


Carbs: Keihin 31A CRB
Variation of the CB21 carbs (?)

Main Jet: 99101-393 - 8mm long, 6mm round head
Stock size: 75
Purchase: Found at jetsrus and dime city (cannot find the latter at the moment).

Slow Jet: ?
Stock size: 110
No idea on the part number

Fluid needle: ?
Stock size: 20
No idea on the part number


Any help is greatly appreciated. I would rather not buy a new carb set yet and just jet these up a little higher if I knew the part numbers for slow and fluid.



Stock jets in question:





Carb Model Number:

 

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The popping could be caused by leaking/inoperative air cutoff valves. The 7 stickies at the beginning of this section of the forum cover most of what human-kind knows about the VB carbs but I don't think it explains how those carbs got on your bike. You might start with the last one, VB Carb Circuits, as it explains how these carbs work quite well.

Fuel Supply and Carburation

Sounds like you have a good approach to the issue and, short of finding a set of VB2 carbs that were stock on your bike (at least the US version), you should have it running the way you want without too much trouble.
 

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The slow jet may not be removable. The 31's are European and maybe Canadian versions of the VB21's. Member Maximus86 knows more on those.
 
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