Topic: #3 Throttle Valve out of sync on CB550F

[olmy]

First off, thank you, everyone, for the many postings that helped me through my first complete disassembly, cleaning and rebuilding of the carbs on my CB550F.  I thought it all went extremely well, until I peered into the intakes.  The #3 throttle valve is way out of sync from the other 3 throttles.  For example, when the throttles are all closed, the #3 throttle valve is roughly 20% open and cannot be adjusted to a more closed position (the screw is at the stop).

I was running out of time after I got it reassembled (had to go to work) but I removed the cover and poked around and it looks like everything was reassembled exactly the same as the other carbs.  I'm hoping that I did something wrong that I haven't spotted yet, and that I can easily fix it, however, I suspect that it may have been this way already.  I’m going to dig into to it further tomorrow.  I just recently got the bike and I never really had a good look at where the valves sat relative to one another before I took it apart.  I fear that the horizontal arm running thought the head of the carb, that the throttle link arm bolts onto, is the wrong part.  Could it be meant for carb #2 or #4, and was installed upside down to work with carb #3?

I have the following questions:

1) Is there any other way to adjust the individual throttle valve position other than the adjusting screw on the adjuster holder?  You can't adjust the position with the bolt on the throttle shaft, can you?

2) There isn't any reason that the #3 throttle valve is supposed to be more open than the others?

3) If this is how it was in the first place, how hard on the engine is it to have one carb that far out of sync?

I was thinking I could test my theory that the arm I mentioned before is the wrong part, by switching it with the #1 carb’s arm, and see if the problem moves to carb #1, but I thought I’d see if anyone has any insights before I start tearing the thing apart again.

[TwoTired]

1) Is there any other way to adjust the individual throttle valve position other than the adjusting screw on the adjuster holder?  You can't adjust the position with the bolt on the throttle shaft, can you?

Yes, you can.  If I understand your problem description.

2) There isn't any reason that the #3 throttle valve is supposed to be more open than the others?

No

3) If this is how it was in the first place, how hard on the engine is it to have one carb that far out of sync?

Unlikely to have mechanical damage, but there will be a whole lot of shakin goin on.

I was thinking I could test my theory that the arm I mentioned before is the wrong part, by switching it with the #1 carb’s arm, and see if the problem moves to carb #1, but I thought I’d see if anyone has any insights before I start tearing the thing apart again.

The arm pivots on the shaft with lock bolt loose.  Center the normal sync adjusters, and turn the arm where you want it and lock down the bolt.  Then go back a fine tune the synch.

You didn't manage to install some slides backwards, did you?  The slide cutaway would be facing the wrong way and appear more open than the others.

Cheers,

[Bodi]

I would take a close look at the lift linkages, the double one between the carbs and the one on the slide lift arm inside the carb cover. Make sure the #3 one looks the same as the others! The inside one could be assembled wrong so the ball is above the upper carbon thingy, that would set the slide higher. I don't see how the lower ball could be in the wrong place but anything is possible I suppose.
I think because of the slide locating tang, you can't have only one slide reversed; two or all four would have the cutout facing in.
The only other possibility I can imaging is a blocked emulsion tube that the needle can't get through so the slide hangs up.

[olmy]

Thanks for the replies. 

The arm pivots on the shaft with lock bolt loose. Center the normal sync adjusters, and turn the arm where you want it and lock down the bolt. Then go back a fine tune the synch.

If I'm thinking of the same part, I can't move it with the lock bolt loose because the bolt actually threads into the shaft, so it fastens into that position.  This is why I fear that it might be the wrong arm.

I would take a close look at the lift linkages, the double one between the carbs and the one on the slide lift arm inside the carb cover. Make sure the #3 one looks the same as the others!

You are talking about the shaft that is oriented vertically inside the cylinder of the throttle valve right?  I just had a look inside and I compared #3 with #1 as they are oriented the same way.  They look identical and it doesn't appear that the ball is under the carbon seat thingy, but I'm going to pull the carbs back off the bracket and take the valves out and compare them.  I disassembled and then reassembled each carb individually before moving on to the next so there is no chance I mixed up parts, and thanks to the little guide, the throttle valve isn't turned around.

The only other possibility I can imaging is a blocked emulsion tube that the needle can't get through so the slide hangs up.

Is that the perforated tube in the float chamber that runs from the main jet into the bottom of the venturi?  I removed it and cleaned it out so I don't think there is anything blocking it.  Plus the adjuster screw is bottomed out so it does look like it is adjusted as far as it can go, and doesn't appear that the needle it running into anything.

I really wish I had looked to see if the throttles were like this before I took it apart.  It ran pretty well considering it hadn't had much attention from the previos owner.  The idle had to be set close to 2000 rpm, and it had a bit of a flat spot but it seemed to run fairly smooth.  Would it have been obvious this problem already existed?  This is my first bike so I don't have a great frame of reference.

Thanks for the help.  I'm going to pull the carbs back of and take a closer look.  I'll take a couple pictures.

[olmy]

Me not so smart.  I just figured something out.

I knew I could always bring the other throttles back up to match #3, but I figured because it was sitting about a quarter open, this would leave me with way to fast an idle.  I forgot all about the idle adjuster!  Stupid newbie.  So I have brought throttles #1, #2 and #4 up to the level of #3 and  adjusted the idle stop down so I can completely close all four throttles, so I have full range movement.

So my only question now, is that OK?  Does it matter that #3's adjuster screw is significantly different than the other three, who all match up quite nicely?  Am I good to go or do I need to figure out why #3 is a bit different?  Below is a link to a picture of the difference between the adjuster screw on #4 as compared to #3.  #1 and #2 are almost exactly the same as #4.

www.theolmsteads.ca/carb

Does that matter?

If I am good to go, where should I set the idle?  Once again I should have looked in before I took it apart, but I have no idea how much of an opening there should be at idle.

Thanks