Single carb conversion tuning

[Whiskeythrottle1]

Hey guys,
Im new here, just finishing up a ground up bobber build with an xs650 with a 2 into 1 manifold. I’ve got a zenith 13859b carb off an old Harley I’m trying to run on it. I’m running into some issues with the jetting/tuning. I’ve played with the adjustable jets and it’s just not running right, Anyone have any experience with this that could throw some knowledge my way? Here’s the bike just for shits and giggles:

 

[gggGary]

might want to show us a close up of carb and manifold.
A 38mm non vacuum carb is pretty big for an XS650. Since the cylinders draw 360 degrees apart you don't really go up in carb size with just one carb. As Mr Grizzled will say a too big carb has poor vacuum signal means you typically need bigger jets than you'd think. But my first concern would be manifold design details.

 

[gggGary]

Lots of cool touches on there, craftsmanship looks great! Got any heat shields 'tween exhaust n carb? Looks mighty warm round there from what I (barely) see.

 

[Whiskeythrottle1]

Here’s the carb and the manifold, that’s kinda what I was thinking, that maybe this carb is just too big.

Can it be jetted down at all? Obviously tuning is not my forte and I’m not familiar with these carbs, it has an adjustable main jet and another jet coming in from the bottom (looks like the drain plug but it’s a jet)

 

[Whiskeythrottle1]

The manifold is designed so the intake from the carb comes in from the top, dead center between both cylinders

 

[gggGary]

Sorry I don't know that carb at all. Adjustable main jet is interesting!

 

[Jim]

Adjustable high and low speed mixture screws. Looks like an oversize chainsaw carb.

 

[Whiskeythrottle1]

Looks like I might just end up getting a different carb. Any idea what direction to look for carbs that would perform well on this setup?

 

[TwoManyXS1Bs]

That carb kinda reminds me of my old Linkert.

... my first concern would be manifold design details.

Ditto. Some discussion on 2-1 manifold distribution balancing in here.

http://www.xs650.com/threads/2-into-1-intake-crossover.27063/

With a large carb, the fitment of the throttle plate in the throat must be precise. Some ideas in here, post #90.

http://www.xs650.com/threads/on-the-road-again-at-40-the-bike-that-is.49360/page-5#post-511978

 

[XSLeo]

Most any of the stock XS650 carbs will work. Just use one carb. Most any Mikuni VM 34-36 mm carb should work.
This site knows those carbs.
Leo

 

[Whiskeythrottle1]

Awesome, thanks I’ll try to pick up one of those carbs!