TOPIC:

In my opinion, I wouldn't worry about this. If the diaphragms are without holes or cracks and retain some reasonable pliability, they're good. There will be inherent creasing as they flex when handling but I suspect once positioned correctly under a secure carb-top, the equal force of vacuum across the diaphragms entire surface will eliminate those creases

The slides need to fit their bores with a fairly tight tolerance. Air bleed past them is intended to be minimal/negligible. However, while needing to be as "sealed" as they do, they still need to slide easily enough for the vacuum to actuate (lift) the diaphragm - which in turn raises and lowers those slides. If you turn the carbs upside down then right way up and give a bit of a shake, the slides should drop slowly. To do this the air between the diaphragm and the carb-top will either be getting displaced or replenished via the venturi. As you rotate the carbs back and forth you'll hear hissing as the diaphragm moves air in and out of the diaphragm chamber. This is why the (dark anodized)center guide-post of the slide-holder is hollow. If you look into the carb-body, down into the bottom of the bore for the center guide-post you'll notice that it is cross-drilled into each venturi. This is how the diaphragm receives it's operating vacuum. It is also the restriction which slows the slides travel when your tipping the slides back and forth.

The slides on my '80 carbs (just finished the annual over-haul) as well as those of the '79 set I rebuilt recently will not always slide up and down freely by merely rotating them. Sometimes a little "jiggle" is required. If yours aren't jammed or seized - they're fine.

With all due respect to the suggestion of oiling: I would never oil mine. Don't polish them. Don't wax them. Don't coat them with anything ! Don't attempt to "remove" scratches. Don't do anything to them in an attempt to "enhance" their operation. Clean and dry will avoid any foreign material from sticking to them and eventually drying to a sticky film which will impede if not prevent their operation. Clean them with a solvent to remove any surface film and dry with a clean cloth. Before installing them into the carb-body give them a final wipe. This applies equally to the slides bores. Small scratches are a sign that abrasive foreign material has entered into the carb via a dirty or damaged air filter or a leak in the air box. If a slide sticks, will only partially rotate in in it's bore or catches throughout it's normal travel then that could be an indication that it has been dropped or otherwise damaged. In this case the slide needs replacing.

Re: Needle holders.

Go back the the '79 carb rebuild and note the pictures of reassembly of the needles and slides. They show a specific orientation of the plastic needle holder with respect to it's home in the bottom of the slide. A "pimple & dimple" arrangement prevent the plastic needle holder from rotating in the slide which could wear both pre-maturely. Likewise, the top of the plastic needle holder has a semi-round notch which when engaged in the steel slide-hanger prevents the slides from rotating, for the same reason. The correct orientation of the needle holder is maintained by the off centered pimple on the bottom of the needle holder engaging in a corresponding dimple in the slide bottom, where it rests. The plastic holder is then held in place with an "inside" cir-clip. If the pimple doesn't sit in the dimple the holder will sit angled to one side and not fully bottomed and strait-up. In this case you can not get the cir-clip engaged fully in it's groove. This has a direct and negative affect of holding the high-speed needle off center with the slide and the needle tip can be damaged when it does not align with the jet but rather "center-punches" the venturi bottom during assembly, due to the misalignment. Additional concerns too with unwittingly completing the assembly incorrectly and having 1 or more cir-clips ready to "spring" out of position which will release the needle and render that cyl. useless.

Again, my opinion. Hope it helps

Pictures are of the freshly re-conditioned carbs from my '80. Complete re & re. Where I painted the '79's with a "black wrinkle" I thought I'd go 'gloss" black on these. Hardly a "show" polish" but as an everyday rider it's shiny enough and looks pretty good on a bright sunny day! Frequent wipes with a soft cloth keeps the polished surfaces surprisingly fresh. The "Frankenstein" like socket-heads I had installed 30+ yrs ago no longer appealed to me, so I used S/S button-heads on this reassembly. Soon as the weather warms ( another couple of months ) I'll take the bike out and run in the 79's I rebuilt this past winter. Don't expect any surprises as the '79 needle is non-adjustable. (other then shimming "UP"). Then I'll replace them with original 80's carbs. Originally intending on keeping them as a spare set, I may sell the '79 carbs.

Fantastic, I will now re-build the carbs and try then in the bike. The slides will come down with a bit of a jiggle and they do not jam, the centre guide holder on my carbs however is not black, its more of a grey colour and looks like it has worn but as I already stated, with the carb tops off the slides go down very easy with no noticeable sticking at all.
Happy days - carbs back on tomorrow and I will give the beast a whirl and hope it starts and idles well.
Thank you all for you help and a big thanks to Scotch for the superb post on cleaning with thinners.
Just a quick question though - what does the small diaphragm do on the side of the carb?

Re: The small diaphragm on the side?


Read your manual "Grasshopper"

Hi Holger,

After I played the swap game and identified which slide was causing the binding. I found that I could see that the nylon post was just a bit off of center. Ever since then I've either rolled the slide on my work bench or just rotated it in my fingers to see that the post was concentric with the slide before I put it back in the carb.

That small diaphragm is the coasting enriching circuit. I believe it's intended to prevent backfiring on deceleration. You will find it on page 171 of the service manual. Before I figured out that my rich condition was caused by soggy floats I plugged the opening in the carb throat to stop that whole system from getting a vacuum signal. To this day that enriching system is out of service on my bike and I've never had any backfiring.

Bill

If you drop the piston valves and the diaphragm assembly in to their perspective bores do they fall down to the bottom? if so you should be fine. Just be sure to put the carb top on as I described and try lifting the pistons with your fingers and letting them fall under their own weight. I just finished 2 of my three carbs and if I lift pistons all the way up to the top they won't fall back down. I don't think there's a problem and I'll see when I fire it up. I sincerely doubt you need diaphragms since they don't see fuel or sunlight so shy of a tear in the diaphragm, they shouldn't need replacing. The diaphragms on mine are original 1980 so 34 years old and they're supple (what I would expect if I bought new ones)

I hate to say it but I think you're getting gun shy here after trying to deal with this issue for such a long time. Hang in there, we'll get you through it and once it's running like a charm, you'll be laughing at this experience. Just remember "what doesn't kill you, makes you stronger"

Kelly Clarkson fan eh!