BS-38 Carb alternatives?

[sailor]

I had hoped the EX-500 carb conversion in
http://www.xs650.com/forum/showthread.php?t=13070 would work on my TX750. Unfortunately the center to center spacing for the carbs is 125mm instead of the 120mm on the 650 and the ganged EX-500 carbs won't fit. Are there any suggestions on a better carb to use instead of the BS-38 that would use the same holder (48mm opening)? While the bike is running OK at the moment, the carbs have been problematic, and the current fuel economy seems low at 32 mpg with rather sedate riding.

 

[TwoManyXS1Bs]

Hey, sailor. Went thru your other posts on this. Here's an old trick, highly questionable, might work if you're in an experimental mood.

With only a 5mm difference in carb spacing, you may be able to adjust each carb holder 2.5mm (0.098") inboard. For each carb holder, install 1 screw, then pivot the carb holders inboard to get your spacing. Your choice of screw. Might want to use old carbholders for this. Drill or grind the other hole to match the head. Or, if desired, slot/open both screwholes to allow the carbholder to fit inboard that 2.5mm. Ignore the port/carbholder misalignment for the moment. Fashion some type of oblong washers to go under the carbholder screws.

Then trial-fit those carbs, see how it works. If they don't give satisfaction, well now you know. Othwise, if you like the performance, you may look into a more permanent mount solution, and possible port matching.

Alternatively, could look into modifying the carbs' assembly to match the spacing...

 

[angus67]

could you "un-gang" them? the older 38's were seperate. Most of us here trust the carb holder to hold the carb secure.
I run 34's, and in the early stages of tuning, had some ear-ring backfires. not once did the carbs blow out the holders.
Or like 2many said, modify the carb holder that extra 5mm. I think its justa piece of angle that holds the later 38's together? 5t?

 

[sailor]

I had thought about "un-hanging" the EX-500 carb set but they seem to share a common throttle butterfly shaft. I suppose it would be possible to put in a 5mm spacer, but that's beyond my shop abilities.

It looks like the VM-34 round slides might work, if I could find a mounting to fit. I checked with JBM and theirs are angled and I believe I need a straight mount. Does anyone know if the Mikuni 650 mount for the VM carbs, their part 005-815, is straight or angled? I would like to go with the VM-34 vs. the -36, but that might be an option as they show a mount with the correct spigot diameter and mounting hole spacing (70mm) but the hole sizes are 8.5mm vs. the 7mm on the bike. I suppose I could either just bolt one down and hope it doesn't shift, of get sleeves fabricated to bring the opening down to 7mm.