CB550 PD46A carbs

[badger_eng]

Merci monsieur 🍾

[badger_eng]

So just a quick update on today....

Ran the bike with no airbox just to see if I could see anything happening with the choke butterflies. As mentioned yesterday, they are not sitting horizontally and there is a lot of slop between the choke butterfly / shaft assemblies for carb bank 1-2 and carb bank 3-4.

Fired up OK on full choke and quite quickly depressed the choke button to the OFF position. Semi warmed the bike giving it some throttle up to 3-4 k and as yesterday, engine RPM was slow to fall and hang around 2.5k before slowly dropping. No change to issue with airbox fitted or no airbox at all. When idling or revving the throttle I could NOT see the choke butterflies moving by themselves and potentially varying the air volume into the carb. Good news as this counts out one possible cause.

Removed the carbs and got them on the bench, just for visuals only at this stage, and its quite obvious that the springs that join the two choke shafts are not in the best shape - I'm sure there will be an abundance of these somewhere - NOT 

Tried a drill bit in the carb inlets to check mechanical sync of the throttle bodies and whilst they are slightly different, they are certainly not MM's out - I've ordered a Morgans Carbtune balancing kit so I can get them synced when all the cleaning and checking is done. - Wish I'd kept the set I bought for pennies back in the 80's!

I'll do some reading of the resources on here and elsewhere before I start any serious strippage.

Probably radio silence for a while until I get them stripped, parts ordered / delivered, re-assembly and subsequent re-start.

Thanks again

Pete

[Oddjob]

Try removing the throttle cables and testing again, the hanging could be caused by the cables binding. I am sure someone on here has broken a set of PD carbs and may have the springs available. A lot get wrecked by people trying to assemble them after and not understanding how they go back together. Only ever did one set of PDs and vowed never to do another.

[badger_eng]

Sorry, I should have added... But good for me to add now for clarification.

It was suggested to remove the choke cable by someone to rule out the butterflies not being fully open and I tried this as part of the experiment.

I also removed the throttle cables as part of the troubleshooting AFTER i'd done it with the cables still attached and functioning as normal.

Bike was left ''as normal'' with no airbox, run up and checked, all control cables then removed and tried again.

Just trying to eliminate the obvious before digging deeper.

I've found some springs on a overseas site, cheap'ish but crazy shipping prices. Still got more searching to do. It looks like the exploded diagram below shows identical springs (pictorally anyway)

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However, my carbs have different springs. One that looks correct and one that looks like it belongs in a watch 

I'll do my searching then maybe make a call in the Forum 'wanted' section.

Thanks for your input

[Oddjob]

If the carbs are off remove the inlet manifolds and check the orings in them. Most have gone rock hard over the years and fail to seal, allowing air to get in which will cause the symptoms you describe. The rings are hard to source in the correct size and most sellers say theirs are the correct size when it fact they are not, I’ve seen some that I refused to fit because they were so bad. They are the same size as the tappet covers, you get 12 in a genuine top end gasket set so use something close on the tappet covers and save the correct ones for the manifolds is my advice. Simple to change a tappet covers and save oring, not so simple to change the manifold ones.

[badger_eng]

Excellent tip. Something else to fettle tomorrow after my morning trip to the dentist. Wisdom tooth possibly 🦷 coming out tomorrow so I’ll probably be even more cerebrally challenged in my remaining years 😬

[Johnny4428]

My K3 was always a pig to start even with carbs stripped and cleaned thoroughly. I increased the pilot jets from 42 to 45’s. End of starting issues and runs great.

[badger_eng]

Thanks Johnny, starting is very good actually, it’s just the erratic / random response after giving it some throttle I’d like to solve.
I’ll be opening up the carbs over the next few days and I’ll see what’s fitted. It’s got a 4-1 Delkevic pipe on it so may not be on std jets.

👍

Pete

[Johnny4428]

Yes of course, mine is standard 4 into 4 exhaust plus factory air box etc. Good luck, interesting project!👍

[badger_eng]

Thanks, I’m sure I’ll be leaning on you guys plenty more.

I’ve belonged / belong quite a few forums (as I’m sure many are) but this one is very lively…. Nice to see one thriving.

[Orcade-Ian]

Heck Pete,
What's with having a wisdom tooth extracted?  I've been trying to get some put in! 
Anyway, if you were to decide that the PDs were too much hassle, I have a set of 627Bs here (500) but jetted for 550.  They were on my F1 that I got from JamesH on here and went right through them, zinc plating fittings and the ultrasonic bath individually.  They are on original brassware and the only small issue is corrosion around the outside of the main jets - inside where the jets/o rings locate is fine on all 4.  I ran the bike for a short time with them before locating a set of the correct 069s from the Netherlands and went through them too and that's what I have on the bike. Obviously the manifolds would need changing and airbox rubbers.

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Ian

[badger_eng]

I’ll message shortly Ian. At the point of extraction now 🥳🍾🎂

Many thanks

[mickwinf]

and i have a set of the earlier manifolds if required for the cost of postage.

[badger_eng]

Wow, this must be 1st!

Hull and Scunny working together as a team   

Appreciate the offers gents. I will message you if thats OK?

Please be gentle as i'm now 25% down on wisdom

Pete

[mickwinf]

LOL I like people from Ull as my mum was yorkshire born, dad was a Lincolnshire yellowbelly so I am mixed race! also the Hull accent makes my accent sound posh!!