Engine stalls when throttle applied - new restoration

[YamaMikey]

I'm hoping the carb gurus are out there tonight! I'm just finishing restoring a 1975 XS650B, original BS38 carbs that I cleaned up & replaced needles/jets with a kit from MikeXS.

The top end was rebuilt, new timing chain, etc and installed the basic electronic ignition from Mikes with a new regulator/rectifier. Wiring harness also is new. Here's the problem:

Originally was able to get the bike to fire; it would run for about 3 seconds, then shut down. Pulled the carbs & decided (with a mechanic friend who knows better than I) to replace the diaphragm/sliders. The bike now idles to where I could get a timing light on it, but as soon as I touch the throttle, the engine quits. I fiddled with the mixture & idle screws to the spec sheet and got those set to where it starts and idles 1000-1200 rpm. Hope someone can enlighten me to a next step - at this point I just wanna ride the damn thing!
Thanks!

 

[Bushyeyed1]

Not an expert on BS38s It could be a leak or carbs need sync’d. Maybe this thread in the tech section can help.
http://www.xs650.com/threads/carbs-carburetors.43/

 

[kevski]

Sounds like a fuel starvation problem, check float levels and feed to the carbs.

 

[gggGary]

..... 1975 XS650B, original BS38 carbs .... a kit from MikeXS.
it starts and idles 1000-1200 rpm.

Did you save the original brass? If it were me I'd clean and reinstall the factory pilots. See what happens. I strongly believe "use only factory (Mikuni) brass" in your carbs. Kits often contain the wrong brass.

 

[Brassneck]

If you still have the old jets, you may consider cleaning them up and re-using them. Mike's kit may be suspect.

 

[YamaMikey]

Thanks everyone. I did save the old jets, cleaned them up & installed them today. In comparing them to the replacements, there were some dimensional differences. I also checked the floats against the parts diagram. OOPS!, Rookie mistake! They were installed upside down. So, with all those adjustments, it started up and the throttle works great. Today that bike went down the road for the first time since 1987 - very satisfying! I just finished the final assembly details, will get some good pics & videos in the daylight tomorrow. It will be my profile picture. Special thanks to this forum for helping me get to this point. I'll be sharing part of next month's SocSec check to help support this site!

 

[kevski]

Good, another one up and running