Topic: One little, itsybitsy carb question

[medic09]

'78 750K.  Carbs have been cleaned and rack reconstructed.  Seems good, except for one last detail.  The choke isn't quite coordinated, and it's sticking just a bit.  Near as I can figure, the problem is at the point where the right and left sides of the choke linkage meet up.  Moreso, I think the problem is with the smaller spring on the right side (see pic, with pick pointing to the spot in pic.  say that 10X fast...).

How much do you wind it?  Where/how exactly does it attach (I can't find the before photo I took    I don't think it showed exact attachment anyway)?  How do you know how *much* to wind it?  The left-hand, heavier spring of the two seems straighforward; but this looks like it needs a bit of judgement to get it right.

First time I've done this.  The interior of the Keihins seems easier than I remember my Amals being; but the rack set up seems more complicated.  I'm learning... 

Otherwise, the rack seems fine.  I had a real frustrating time with the linkage arm at the top of #2; the spring kept dislodging.  Everything but this choke thing seems squared away now.  Slides move well, the other springs seem okay to me (unless I goofed on the other choke spring?).

Just one last annoying detail...there's always one last annoying detail...

[kettlesd]

From the pic it appears you do not have the carb mounting plate attached, no? This could be causing the choke prob, as they need to be aligned to function properly.

Its been awhile since i separated the choke halves, but it seems to me that the smaller spring only needs enough tension to maintain contact between the two arms. Only the larger spring does the job of actually opening the choke again upon release by the cable.

If I'm wrong, im sure Eldar will jump in here any second now......

[medic09]

Good call about the mounting plate.  I thought of it a few minutes ago, and everything got WORSE when I put it on.  The throttle/slide mechanism stuck.       I may have tightened it down too much, stressing the whole rack.

So I took it back off for the moment.  Throttle/slides moving well.  Choke still acting up.  I think, among other problems, that the heavier spring on the left is riding over and sticking on a piece of the linkage on the right.  Still can't seem to get it figured out...

Annoying last details...the devil's in the details...

[medic09]

Well, something kept bothering me about the left (thicker) choke spring.  Sure enough, I have it attached in the wrong place.  It needs to attach further back.  The problem is, I had ruined it's shape when I removed it, and so now I have to try and recurve it and stretch it further back to it's attachment point.

Getting late, and I've got a root canal appt in the AM.  I'll try this again tomorrow.

BUT NOW, I have another problem.  I tried attaching the mounting plate again.  Screwed it down just to the end/snug; didn't torque the screws hard.  When the plate is on, the choke mechanism gets really stiff; almost as if the plate is creating a misshape or misalignment of the whole rack.

    

[eldar]

Well it looks ok in the pic but if you rack is not aligned, it will cause binding in the choke. As you may have noticed, the choke flaps are actually on 2 bars, one for the left side and one for the right, If the left and right are not halves are not aligned, one side will move and the other will not. I had this happen to me but It is simple to remedy, if anything put a small drop of oil on the bushings to lightly lube them and that should help.

A final part, this mis-alignment will not affect the slides much since the spring that closes those is very strong.

[jtb]

Remove the mounting plate and the rear mounting plate.  remove the butterflies.  install the mounting plates, then the spring.  I straightened a paper clip with just a hook on one end, then came in from the front side of the rack, underneath the butterfly shaft and grabbed the spring, brought it around to the front, over the butterfly shaft toward the rear of the rack and hooked it onto the lever on the right shaft.  That should have the spring attached, and the carbs aligned.  Now install the butterflies.  If your spring is toast, I may have one.

Good Luck!

John

[medic09]

Thanks, jtb.

Mount the plates *before* the chokes,eh?  It's worth a try.  I actually have another spring (I think) from another set of carbs, if I need it.  I just had hoped to straighten this out (I mean recurve it!) without any disassembly; but I'm game.  I'll try it your way.  What's the logic.  Alignment of the rack make a difference before mounting the chokes?

While we're on that, the original brass screws for the chokes were peened at the factory.  I don't have a way to redo that.  The shop manual says to toss them out, and use new screws with a special lock washer (there's even a diagram in the manual).  They don't come in the Keyster kits, I know that.  Anyone actually do this?  Or do you all just firmly reinstall the original screws?

Thanks!

[eldar]

guess I just used the regular screws.

One thing I remembered this morning was that the plates can move side to side ever so slightly. I have had this cause binding for me as well. Just one more thing to look for.

[medic09]

guess I just used the regular screws.

One thing I remembered this morning was that the plates can move side to side ever so slightly. I have had this cause binding for me as well. Just one more thing to look for.

Mine did, a little; but I thought they aligned when I screwed them into place.  Do you mean the subtle shift that the whole length of shaft can do?

Thanks!

[jtb]

I just used the regular screws, too.  They have stood up through 5 or 6 disassembly and reassembly ops.  The racks align the carbs.  When they are mounted, open the throttle mechanism, and slide the left butterfly shaft as far to the left as you can, so that the tang fits between the throttle pully and the stop.  Then set the spring.  Good luck.

John

[eldar]

No not that shift. The holes in the plates are slightly larger than the screws, it is this change that I am referring to.

[medic09]

No not that shift. The holes in the plates are slightly larger than the screws, it is this change that I am referring to.

I didn't think of that, thanks.  I'll check how they line up before tightening.

[eldar]

I had to do that with mine. That choke was kicking my ass and I tried it just cause and well, I really felt stupid then!

[medic09]

Okay, so I messed up more than I thought.  Hehehe    Turns out where the right and left halves interface, I hadn't set them up right.  Sooooo...the heavier (left spring) wasn't attached right, had to be further back on the rotating piece; the lighter spring (right side, that pulls the two halves together) was backwards.  Had to remove two carbs from the rack to remove and re-place it correctly.  And one of the nubbins on the left rod had to be placed a little differently.

Got it figured it by playing mock-up with a carb, rod, and springs from a spare rack.  Kinda like in "Apollo 13".  Well, okay; I'm not that (NASA) bright or I wouldn't have done this to begin with.  I have a very shallow learning curve...  Also found the before photo I took of that choke linkage in my laptop.

NOW, it's pretty straightened out except...

I tested the choke linkage by running a wire through the arm where the cable would go.  The chokes close only about to 3/4.  What detail am I missing now.  Do I need to put one more wind on the light spring?  Or...?   

Well, at least I'm getting an education!  ('course, I'm not getting my schoolwork done...)

Thanks guys!

[jtb]

You probably still have a little binding on one of the butterflies.  Loosen their screws just a bit and try it, if it works, then one of them (or more) was slightly misaligned.

[medic09]

I'll try that when I get home later.  It seems to me that the whole assembly moved towards closing pretty well; but when the arm was fully extended, the flaps/chokes were only about .75 closed.

Yet, I was wrong before on this, wasn't I? 

[Tvag]

I agree. Having just taken apart my carbs and not knowing anything about what I was doing I learned a lot. I was having the same problem with the choke not moving freely or closing allthe way. For me it was the butterflies. Loosen all the screws just a turn or two until you see that the butterfly's are not locked in place. Then try the choke again. It should move completely freely the full range at this time. Butterflies opening and closing as they should. NOW, somehow using a rubber band or whatever you can find, keep the choke fully engaged (closed) and tighten the butterfly screws. This way they are positioned correctly for fully operation. Be sure to have the mounting plate on while you do this. The carbs need to be in thier final position.

Also, I read somewhere not to reuse the old screws. Apparently the vibrations of the bike can knock them loose and you are suppose to buy new screws so they fit very snug. I reused the old ones anyway and just included some Loctite thread locker on them. Again, I'm completely new to this but just thought I'd throw the info out there.

Good luck.

[medic09]

Tvag, your insight is right on.  That, in fact, is what I've already done.  Nonetheless, I had previously thought I set these guys up right (and hadn't!), so I'll try it again later today.  Sometimes I do need to do these things over a few times to get them quite right.  By hand, they seem to close just fine, and don't *seem* tight/constricted; but we shall see...

BTW, what you did with your screws is apparently what most of us do.  Mine are beginning to lose their slots, though.  I may take a few screws from my spare rack.

Thanks guys! 

[medic09]

Looks like you guys were right.

WooHoo!  Another thread retired.   

Okay, what was I going to work on next?

[Bob Wessner]

Okay, what was I going to work on next?

I think it was schoolwork. 

[medic09]

Okay, what was I going to work on next?

I think it was schoolwork. 

Yaknow, Bob, I'm almost 50.  My dear mother still asks whenever I call her, "so, what are you supposed to be working on now?".  As if I would call her just to procrastinate on my schoolwork.  Like just know, when I read your response instead of the AWFUL paper I'm supposed to critique for the qualitative section of my graduate research class.  This will in NO WAY enhance my patient care, whereas reading this forum pragmatically contributes to the upkeep and repair of my means of transportation.

Actually, I was thinking more of running down to the local repair shop to get some new fuel line to complement the nice job of cleaning my carbs.  Later I might get started on tune up stuff that might as well be done before the carbs are reinstalled and the engine test-run.  Then I need to see about borrowing a friend's carb synchronizer, then I wanted to remove my old hardbags and mount the taillights so I can get those repaired and cleaned up, tomorrow I'm supposed to bring the tank and side covers to the body shop for an estimate on painting, then... 

Truth is, I've hated school since about 2nd grade, but I keep going back because I love to learn.  The amazing thing is they keep allowing me to finish and move on...