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CB550 PD46A carbs

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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  ;D

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)

[ Guests cannot view attachments ]

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

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.

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