rpm jump

[djfeth]

Just got my 79 xs11 running, new carbs and alot of electrical work and misc. But nowI start it up and it will idle for a few mins then the rpms will jump from 1k up to 6k and stay. I havent seen any vac leaks and it happens if you never touch the throtle.... any suggestions on what to look at? This is the first bike I have worked on and its about to cause brain damage from me beating my head against the wall...

[thewiz]

Well ... a stuck

advance mechanism could be responsible for some of the extra rpm ... but beyond that ... and I hate to be the bearer of bad news ... it is likely going to be in or on the carbs.

Did you bench synch before installing or dynamically synch after the installation?

You didn't say but: are they new aftermarket carbs or 'new to you' BS34 II s? Any other mods? Give us the whole story, my man

[ross]

d*mn carbs.....

hey there djfeth......i agree with thewiz....we gotta know more about what ya got...if ya can do photos, that would explain alot with out a lot of typing....could be idle screw adjustments or something more serious.....trust me if your carbs were not cleaned to this point of cleanliness...




then they were not cleaned....also, here is the link of the h*ll i went thru to get mine back in shape....

http://www.xs11.com/forum/showthread...threadid=17116

also ya might wanna use the search function and search either carbs or rpm's or both to find an answer....trust me, the answer is here, just how bad do ya wanna work for it.....good luck.....talk 2 ya later....ross

[prometheus578]

On the left side of the carbs... you will see a little lever.
This is the choke lever(Actually, it's an enrichener system.)
Anyway... one pulls the lever out when starting the bike cold.

But nowI start it up and it will idle for a few mins then the rpms will jump from 1k up to 6k and stay.

Uhmm.. that will happen if one doesn't take the choke off. (as the engine warms.. it runs better)
Of course, it could be something else. This one just popped in my head.

[thewiz]

"...will happen if one doesn't take the choke off...."

Do ya' think? When I leave the enrichener on at idle, it usually eventually just loads up and dies? Maybe I got something wrong .... but I s'pose it's possible ... 'specially if a throttle valve or valves remain open.

[planedick]

I'll bet

It probably is a synch problem. A proper synch will solve lots of seemingly tough carb issues. I struggled with my carbs just trying to get the even idle perfection I knew was there using my Motion Pro mercury synch tool. It wasn't until I visited Thewiz and he used his Morgan CArbtune synchronizors that I finally acheived that. Another thing I learned while there was that a vacuum can build at idle that will advance the timing and cause a runaway idle too. Try removing the vacuum line to the vacuum advance unit, cap the carb port and try it again.