72 XS2 carb issue I can't figure out

[Oldnwiser]

I was out on a little train trip.....Anyway back to your carb issue. I'm wondering if during the ultrasonic cleanings, the needle jets were removed and verified clean (perhaps ID #)?

A generally accepted - around here - source for genuine Mikuni brass is
http://www.nichecycle.com/ncs/categories/carburetor/mikuni-parts-by-category.html

They're not genuine Mikuni, but Niche does also offer a house brand of needle jet (Z6) and a needle (4JN19) that they spec as replacements for '72 (306 model) BS38 carbs that are perhaps better than other aftermarket (I have some for pending resto). However, will reuse original if possible.

http://www.nichecycle.com/ncs/catalogsearch/result/?attr=0&q=256-14941-86-00

http://www.nichecycle.com/ncs/categ...ng-tuning/needles/102-3650-needle-by-ncs.html

If you’re using the BS 38S have you checked the throttle valves for the plates for a vacuum leak? Also are the diaphragms good? And lastly are the tops over the vacuum diaphragms flat or do they show any evidence of over tightening or warpage. I hope that this helps.

 

[xshead]

I could just be "blowing smoke" haha, but are the XS2 carbs racked?
I was having this exact problem on my recently purchased 79 XS650. I went through the carbs to get it running reasonably. I got it started and it would smoke when revving. I really thought I was in for a top end rebuild until.......... I had noticed that the bottom angle that keeps the carbs racked was missing. I fabricated one and bolted it on. The bike is perfect now. Hard to believe.

Hopefully it's something as simple as this on yours.

 

[TX650A Van Islander]

What do you mean by "racked"?

 

[xshead]

Both carbs mounted together as a solid unit with brackets.

 

[gggGary]

70 to 75 Two separate csrbs no rack but a good heads up

 

[TX650A Van Islander]

I suppose that's another good reason for me to install the '76 carbs on my '74.