Topic: Proper procedure for adjusting throttle linkage.

[NGL_BrSH]

I'm getting real close to getting my CB550 K1 1975 running right.. fixed rich problems in the carbs and synced them up.

I've done the timing, rebuilt carbs 4 times, tappets, points/dwell, idle mixture is good.

my problem is randomly when i pull up to a stop light or sign the idle heads for about 3k.  Sometimes blipping the throttle will fix it, sometimes it just comes down by itself and usually wants to stall out at that point because it's suddenly too low.

When I synced the carbs it took about 20 mins and she purred when i was done.  During that sync once when i blipped the throttle it went to 3000 rpms and i watched the #3 carb vacuum drop fast.  Not sure if that has anything to do with it.

The little metal tabs that cross between the syncing screws (for a lack of better terminology) are fairly mangled and not flat.

The throttle handle does not "snap" back but I can manually close it by rolling it forward.  I noticed that there are two throttle stop screws on the linkage near where the cables connect.  when i open the throttle 100%, the linkage hits this screw.. when i release it it never hits the other one.. unless i roll the throttle forward.  Regardless of what i do to the cable (even disconnect) it will never rest on the closed throttle screw..

I'm thinking that 4 separate carb pieces are not properly attached to the arm.

I know that was really confusing but hopefully you can follow.  I'm searching for the proper way to loosen all the arms from the throttle linkage shaft and adjust it.

[bwaller]

Is this screw you speak of the idle adjusting screw? Large head with a spring on the right side of the carbs?

How are your cables? Most often the problem is no free play in the pull cable, lousy cables, improper routing of the cables or the throttle sleeve is bound up on the handlebar.

So a good exersize is to;

lube or replace the cables, and adjust so there is some free play. (that adjuster is in the cable near the handlebar switch)

Remove the throttle sleeve from the right h-bar switch to clean.

Route cables so nothing binds and the throttle snaps shut with handlebars both full left and full right.

[TwoTired]

The individual slide adjuster have more adjustment travel than the idle stop screw.  If your idle stop screw isn't the master control of your idle speed, then the tension on your throttle cables is setting your idle speed, and this is not as precise as the throttle stop screw.

This is often the offshoot of bench syncing carbs with a drill bit.  The slide alignment should actually start out with the travel adjusters set for allowing the slides to reach full closure of the carb bore, rather than drill bit height.  Then the throttle stop is what keeps the slide open just enough for idle and is the determining factor for idle speed.

Your solution is to screw out ALL of the individual slide adjusters enough so that they allow the slides to close fully, with the main idle knob backed off.  Then crank in the idle knob so the bike will start.  Then vacuum synch three carbs to one that you pick as the master carb.  This will prevent you from twisting all the adjustments, so that you loose full carb slide travel.

Also, make sure ALL tension is off the throttle cable when the carb slide travel is resting on the idle stop.

Cheers,

[NGL_BrSH]

Thanks for your response TT.  Last night when i posted I guess my brain wasn't working.. of course it's not supposed to hit the inner stop screw.. it's supposed to hit the idle stop screw.. which it does.

What i'm trying to confirm is the position of all 4 linkages on the shaft..   should i loosen the 4 screws and let all the slides down then retighten them.. or does this not matter at all?

Also.. TT.. have you ever been to maine?  if not.. how do you feel about planes

[TwoTired]

 
There is no inner stop screw. 
There are the four slide height adjusters, and the main idle stop screw.  There are also some adjustments to the throttle cables.  But, they are for adjusting the slack on the cables, and should have nothing to do with return to idle issues when adjusted properly.

There is the main cross shaft the actuates all the slide lifters.   The individual adjusters determine how the slide moves in relation to the main shaft.  The goal is to have all the slides positioned equally so that the main cross shaft moves them all equally.  It doesn't matter where the linkage rests relative to the others.  It's the slide position that is important.  And, your vacuum gauges should tell you when they are all at the same position by showing equal vacuum.

Never been to Maine.  Heard it's beautiful, when it isn't mostly uni-tone white.  I'm uncomfortable in extreme cold.  Love airplanes.  Despise most airports that serve airlines.  G.A. airports I like!

But, I think a local mechanic might just be cheaper than air travel from CA to ME.   But, I guess the risk is that the local mechanic has three left thumbs, one of which is stowed primarily in his posterior.

Cheers,

[NGL_BrSH]

haha.. all the local bike mechanics are like.. "points? I think you put a dollar bill in there and tighten something up and its all good"  Truly.

Maybe after much more of this I'll assume the role of the local bike mechanic.

Ok back on topic. 

So I'm trying to figure out my sticky high idle still.

Let me ask you this.. If you bike is idling.. and you reach down and press on one of the brass caps that cover the slide adjustments does it change rpms?

When i do this to any of hte four.. the idle drops back down.. until i rev it again.

Just want to make sure it's normal.  It's mainly having idle issues when it's all warmed up but i'm just ruling out sticking linkage slides.  I don't see how the linkage or slides could be doing it because they've be apart so many times and lubed a lot.  Every time back on the bike same thing.. long time for the idle to drop and then once it does drop.. it won't stay running unless i increase the idle stop screw.. which in turn brings it back to 3k rpm.

I'm thikning about just buying another set of carbs on ebay, rebuilding them meticulously and swapping them over to see if there is any improvement.  It's either that or maybe i'll try a new spark advancer.

[TwoTired]

Let me ask you this.. If you bike is idling.. and you reach down and press on one of the brass caps that cover the slide adjustments does it change rpms?

yes.  The linkage can be deflected with pressure like that.  Further, the ball joints in the linkage have spring pressure tension to keep wear for creating uneven slop in the linkage.  Your thumb can easily compress these springs.  The springs normally have to resist throttle slide friction, not the weight of a human focused on one thumb point.

When i do this to any of hte four.. the idle drops back down.. until i rev it again.

When you do that, one slide closes more than the others.  An engine running on only three idles lower than one hitting on all four.  If you had you gauges on it, you would see the thumbed slide showing a vacuum reading different than the other three.

Just want to make sure it's normal.  It's mainly having idle issues when it's all warmed up but i'm just ruling out sticking linkage slides.  I don't see how the linkage or slides could be doing it because they've be apart so many times and lubed a lot.  Every time back on the bike same thing.. long time for the idle to drop and then once it does drop.. it won't stay running unless i increase the idle stop screw.. which in turn brings it back to 3k rpm.

These are symptoms of out of sync carb, you know.

I'm thikning about just buying another set of carbs on ebay, rebuilding them meticulously and swapping them over to see if there is any improvement.  It's either that or maybe i'll try a new spark advancer.

I'd see if there are vacuum level unevenness changes that correspond to your idle return issue.  (Barring thumb distortion issues.)  If you want to mash something, mash on the big bell crank where the cables fit.  That should apply pressure to all slides simultaneously.  And watch for vacuum change oddities on a per cylinder basis.

Did you tighten bolt "A" properly.  If not, the arm will slip on the shaft and it won't stay in sync very long.

Cheers,

[NGL_BrSH]

thanks for a very indepth detailed response as always

unfortunately A bolt is tight.. I've taken them apart 4 times and reassembled them 4 times.. all with teh same idle issue.. as well as sync the carbs.. I found it to run much nicer at midrange with no surging, however the idle issue unresolved.

I'm going to take apart the spark advancer tomorrow night and see whats up.