Topic: Carburetor Stay Plate/Shaft

[Nduetime]

I just completed cleaning and rebuilding the carburetors on my 1975 CB550. I have a questions regarding the carburetor stay plate. I've attached the exploded parts diagram to better help illustrate my problem/question. I understand the image is of an exploded diagram from a CB500, but the quality is better and looks nearly identical to the CB550.

I completely disassembled the carburetors but left everything intact for the stay plate that the individual carbs bolt to. Somewhere along the process of cleaning the stay plate by hand, the rotation action on the shaft went from freely spinning action to that of something slightly less. I wouldn't say it's stuck but it there seems to be something interfering with the shaft spinning. For example, with the plate in the upright position as it would bolt to the bike, I could twist the shaft to simulate throttle. When I let the shaft go, it would fall back to it's resting spot with ease with nothing more than gravity. Now, it does the same, but it just take a little more effort for this to happen. This is without any of the carburetors attached. 

Does the shaft have any o-rings or bushing that might need to be replaced?

[bryanj]

It does have bushes but they are not available, what can happen is there is a small peg that you have to drill out to remove the shaft and if the shaft is pushed one way(cant remember which) the bush gets damaged.
There was a member on the uk site that was getting some stainless shafts made, not cheap and i dont know if there are any left, forum name was oddjob

[Oddjob]

I've seen a carb stay plate where the internal bushing had cracked, it's possible this may have happened in your case. However I suspect that was due to someone drilling the retaining pin out and not getting all of it removed, they then attempted to remove the shaft, which it does by sliding sideways, however when it wouldn't move they hit it and the small remnant of the retaining peg broke the bush as it came free. It is also possible that some dirt/grit etc has managed to get into the bushing area and that's causing friction.

You can quite easily remove the brass retaining pin, located in the left hand tower, looking down on the plate like you would sitting on the bike, just use a 3mm drill and drill it out. When the shaft moves sideways you've got it all, now remove the clamp bolts on the lifting arms, slide the left one off, loosen off all the butterfly fittings, maybe take a pic so you know how to reassemble it. Remove the woodruff keys under the lifting arms and slide the shaft out, sounds hard but it's very easy.

See if you can then locate what's binding, using just the shaft. If the shaft is corroded (and most are, from heavy surface rust to bad pitting) you can replace the shaft with a stainless one (I have a few left) or take it and have it hard chromed (done that as well) once you've got it moving freely, tap the drilled hole for the retaining pin to 4mm, fit a dog point screw after modifying the dog point so the point sits inside the groove cut into the shaft, I just fit the dog point into a electric drill and gently lay a file on it whilst it's spinning, soon files down to the size required. Then refit everything, maybe consider whilst it's apart having all the butterfly fittings bright zinc plated, makes a huge difference and makes the whole thing look brand new. Maybe have the bracket powder coated at the same time, or if your really posh go for ceramic coating, I've had both done in the past including having a bracket ceramic coated in a chrome like finish.

OR, just buy a new bracket if that sounds too hard, I have a NOS one left if you want to go that way.

[Nduetime]

Thank you for the replies. I cant say for certain but I highly doubt someones gone in and attempted to drill out the retaining pin. It was my late fathers bike with low milage and has been in the shed for the past 30+ years so I don't suspect there is not much corrosion. I'm not saying it's doesn't have it but judging the condition of the carburetors exteriors, I suspect something else is at play.

I cleaned the plate by liberally spraying carb cleaner over it, wiping it down, using compressed air to completely dry it off, followed by hand polishing with Mothers aluminum polish. I can't say with 100% accuracy, but I really thing the difference in play came when before/after I sprayed carb cleaner on it. I didn't correlate the two at the time, but reflecting back on it now, I really feel this was when it happened.

My thought is that if the shaft came lubricated at the towers, I very well could have washed that away? I wonder if what I am experiencing might be just friction between the two surfaces? If this is the case, would it be possible to apply a lubricant to the shaft at the towers using a precision oiler pen?

Maybe I'll spend a little time this weekend taking a closer look at it, take some photos/video of it in its current condition and post them for a second look. I'm not the most knowledgable in motorcycles, just someone looking to bring his fathers bike back to life.

[Oddjob]

I wasn't saying that it could be that drilling out the retaining pin was the problem, just that that's what caused the damage to the one I'd seen with the broken bushing. You'd know if the pin had been drilled out, it's pretty obvious.

It could also be the compressed air that caused the problem, that would have driven the carb cleaner down the shaft and it may well have dissolved any lubrication Honda put in there. Saying that the bush is either brass or more likely phosphor bronze so may not need any lubrication in order to work. I usually oil mine when reassembling with some silicon oil, so you could try dribbling some oil down both bushes and see if that helps.

Either way it doesn't sound a big problem, just one of those niggles you get every now and then.

[Nduetime]

OK. Phew! I was worried the bushing might have been plastic and the carburetor cleaner might have eaten away at it. I had a hard time sleeping once I read there was a bushing in there. I'll try the silicon oil and see if that helps it out.

My concern is/was that any friction due to lack of lubricant, corroded shaft, or faulty bushing could potentially cause the bike to have a hanging idle condition. I am probably overthinking it because the return spring will assist in its return rotation, I suspect.

[Oddjob]

And the return spring on these carbs is powerful, makes your wrist hurt holding it open most of the time, one of the good points about fitting the throttle holding screw that Honda fitted to the 500/750, I wind it up when I'm on a motorway so the throttle just holds itself but you can close it with just a gentle movement, it can be fitted to the 550, all the mouldings are there, all you need to do is drill out that protrusion on the lower handlebar casing and tap it to 5mm, then you can fit the ramp (inside) the spring and the thumb screw. Certainly saves on wrist ache.

[Nduetime]

I took a vide this past weekend with the carbs already on the bike. What you would have seen if the video uploaded, was me fully opening the throttle and quickly and completely letting go. I know it should snap back, but you would have seen it just creeps back.i then took another video with the throttle cables off the and me manually actuating the carbs, which would have show it return quicker. I since removed the carbs from the bike and the plate, concentrated some lube on the shaft at where it passes the towers on the stay plate. I then took another video of just the stay plate by itself after removing the carb, and the shaft just freely falls back like it did back before I rebuilt the carbs.
I suspect, the lubrication on the shaft/towers was probably removed in my cleaning process. I’ve since added lubrication back and have verified it’s working properly. Carbs are reinstalled on the stay plate and it feels snappy like it should be. I still need to put them back on the bike but I also suspect I need to replace the cables. I had suspected that I was gonna need to do that, I was just hoping I could get it running to verify I was ok with the carbs until then. Guess not!

[Oddjob]

I suspect your going to fall into the trap that a lot of people fall into, namely, just throw money at it in order to cure a problem. A lot of the time this is not needed and can in some cases make matters worse not better.

Genuine Honda throttle cables for the 500/550 are getting harder and harder to find these days, there are loads of copies out there that look the same and are a lot cheaper. They are cheaper because they are constructed cheaper in most cases. A genuine Honda cable will have a Teflon sheath around the braided wire inner core, an aftermarket copy generally doesn't, not say always doesn't but I can't remember ever seeing an aftermarket copy with the Teflon sheath on the inner cable, they may exist, if so please post a link to where to buy them from.

Over time this sheath starts to dry out, contaminates and grit makes there way into the cable etc, this makes the inner start to drag against the outer, in the past people would oil the cables but this made matters worse, the Teflon reacted to normal oil by swelling, this caused more drag and eventually people would just replace them, usually with cheap copies. If you disconnect your cables and pull the inner out as far as it will go you'll see the Teflon sheath if it's a genuine cable, the inner needs to be fully out though as it starts around an inch or two above the nipples. No sheath and you have aftermarket cables fitted and these are not exactly the best in the world. However you can oil these so it's not a total loss. If they are genuine you can still oil them IF you use silicon oil, the Teflon sheath does not react to silicon oil as it does to mineral oil. I would remove the cables entirely, hang them on a door so they hang nice and straight and just dribble silicon oil into the chrome fittings on the top of the cable. You'll see it come out of the carb end of the cable in an few minutes or so. Work the inner up and down, see if you can feel any snagging, most cables get worn through against the frame, this not only allows the new oil to get out but also allows crap to get in, so check the cables before oiling to see if you can see where it's worn through. If it has maybe use some insulating tape to seal it up whilst you oil the cable. Afterwards you can protect the cable by splitting some fuel line and putting that around parts of the cable where it touches the frame.

By far the biggest cause of drag on throttle cable though is incorrect routing, Honda knew this and issued cable and wiring diagrams in order for the mechanics doing PDI and building them out of the crates to route the cables correctly. The 550 has a diagram in the 500/550 addendum, which I believe is available on the site somewhere but just in case it isn't I would suggest this. Remove the cables from the R/H handlebar switch entirely. Remove the throttle tube with it's rubber grip, oil/grease the handlebars and slide the throttle tube back on, spin it by hand until it feels really free. Then refit the oiled cables, thread them over the top yoke, they pass through the gap in the speedo/tacho bracket and then pass around the headstock on the left of the frame, around the outside of the frame member, below the rubber mount for the tank and pass through the frame where the coils are mounted, above the coils obviously, a small ziplock is used to hold the cables against the frame just as they exit through the frame. They then attach to the carb bracket. Check before attaching that they move freely, they should feel like it takes to effort at all to move them back and too.

See if that helps with the feel of the carbs, it costs next to nothing to do and should only take a hour or so.

[Nduetime]

This is a video I took today. Carbs are back on the stay plate, mounted to intake, only pull cable attached (routed per the photo found in this thread - not the way indicated for the CB550F).
http://forums.sohc4.net/index.php/topic,183807.msg2127898.html#msg2127898/

The push cable has been rerouted to freely hanging from the left control, no additional bending to impede the action of the carbs.
It appears as though there is an inner sheath for the cable as shown in the photo. However, the additional photo show some wear and slight kink in the cable. I am assuming this is probably not repairable will require replacement.

[Oddjob]

The confusion in the wiring routing diagrams stems from whoever drew the diagrams not dotting the line for the throttle cables when they show behind the frame, the diagram appears to show them on the right hand side of the frame, those cables should have been shown as sort of dashed out in profile to indicate they were actually behind the frame not in front of it. However the rest of the pictures clearly show them routed to the left of the frame member and passing through the coil opening, something they clearly can't do if they were already on the right of the frame.

The kinked cable has had it I'm afraid, replace that one, the sheathing doesn't look right TBH, Hondas is more black and seem to not end abruptly like a tube, it just sort of peters out in a gentle slope. However a sheathed cable is far better than a non sheathed so a similar replacement if it can be found would be ok if you can't find a genuine Honda one.

Should have mentioned this before but there are 2 different lengths of cables, the USA market (amongst others) got higher bars and these need the longer cables than say the UK market which got lower bars with shorter cables. IIRC the shorter cables end in 620 and the longer either 040 or 000.

[Nduetime]

So the goal was switching out the handlebars with a Cb400 (already purchased) which is shorter than the CB550. I am wondering if I shouldn’t get the shorter length CB550 cables that were used in the uk to pair with the CB400 handlebars.

[Oddjob]

I'd compare the 400 and 550 bars first and see what the difference in height/length is but generally I'd say if the 400 bars are lower than the 550 ones go with the shorter cables.

[Nduetime]

Update: I managed to get the video updated by going through a bunch of other steps. I just have to remember to upload from my computer instead of my phone next time.

So here’s a video I took of the throttle action with the new cables that just arrived. If you see anything that needs to be reworked, please let me know. Well, never mind.  I think I’m done trying to upload videos to this site.

Granted these cables are not oem/nos but at least they’re something to get me closer to at least trying to fire it up to see what I’m dealing with. For right now, these should work. I still need to read up on proper adjustment of the cables. I’ll still need to take them back off and lube them up when changing over the bars to the CB400 bars I bought.

[Oddjob]

Watched the video and I have some suggestions.

Firstly though, good job on the carbs they look really clean, the spindle is really good considering it's age, most are pretty rusty TBH, not rusty rusty just speckled with small pin prick rust spots.

The cables I feel will be much too long when you finally get around to fitting the lower bars, however at least you know the cables you've bought work so maybe a set of the same but shorter?

On cables BTW, I was slightly wrong on describing the teflon sleeve, I found some genuine Honda cables in my stash and the sleeve isn't actually bonded to the inner braided wire, I was thinking of the clutch cable for that one, it's like yours, a sort of tube fitted inside the outer cable that the inner runs through, so your old cables were most likely genuine Honda ones.

I did notice a little too much play in the pull cable, usually the adjuster fitted at the bracket end is almost out of adjustment, I tend to wind both nuts right out, the lower one so it's suspended on the inner wire and the upper one hard up against the ferrule, fit the nipple into the hole on the butterfly bracket and then just pull the cable outer upwards by hand, the spring is so strong on the carbs it's very unlikely you start to lift the slides but watch just in case, I've also wound out the idle adjuster screw next to number 4 carb, once the cable feels like it's just about to pull the carbs wind the upper nut down and then fit the lower nut, lock up both nuts. For fine tuning adjustment use the adjuster on the cable on the handlebar end.