Terrible acceleration

[JayDanXS650]

My Mikuni BS38's on my 76 XS650 are in fair condition. The acceleration is lacking. The mid and top are working just fine. I am thinking it might be a bad jet or something but being new to this I am not sure. Any help or advice I can get is much appreciated.

 

[5twins]

A thorough carb cleaning is usually required when you first get one of these. Maybe during that process, you'll discover what the problem is.

 

[JayDanXS650]

I cleaned both carbs, ordered a new jet kit. While cleaning I pulled a big piece of lint or something from the air jet, put it all back together but that didn't work.

 

[CDNTX650]

did you read the carb guide? your cleaning of carbs and the guides are probably different...

 

[JayDanXS650]

I will check on that. Any suggestions for better performing replacement carbs?

 

[malc]

i had much the same problem .it was fine on tick over and midrange and went realy well on full throtle but tickover to midrange was crap .it was a small pinprick size hole in the diaphram ,didnt see it till it was held up to the light .diffrent bike after replacing them both,,,

 

[JayDanXS650]

Where can I get what I need to fix this problem.

 

[littlebill31]

Check out www.amckayltd.com/carbguide.pdf that's the carb guide.
Read it 'til your eyes bleed. It's the only way to understand how they work. As for replacement carbs? Well, I would get to know these forwards and backwards first. Most of the time replacement carbs are more picky then stock and are more of a pain to tune. There is no set recipe for these. There is a lot to these bikes, but once you understand all the little systems, and how they work together, it becomes second nature.

 

[ProSimex]

Also double check your timing, I had the same problem and after tearing the carbs apart a million times and going nuts, turned out to be timing

 

[littlebill31]

Also double check your timing, I had the same problem and after tearing the carbs apart a million times and going nuts, turned out to be timing

Yes, there is an order to follow. Cam chain tensioner, valve lash, timing, then carbs. They must be done in this order. One system works off of the other. You can clean, tear apart, re-jet, whatever, but you are wasting your time if, for instance, the valves are off.

 

[grizld1]

Yep. And check compression after you've adjusted the valves, JayDan. Also, adjust your thinking: "the" problem may well be the result of multiple defects. Inspect everything, and take your time.

 

[JayDanXS650]

Wicked. I appreciate all the help brothers. Ride on.

 

[1974jh5]

If it turns out the diaphragms are bad, JBM Industries has replacements. They are a lot cheaper than the whole slide assembly. http://jbmindustries.com/Yamaha650.html