SOHC.co.uk Forums > CB500/550

CB550 PD46A carbs

(1/8) > >>

badger_eng:
Gents, looking for a little feedback from the group.

I bought michtag’s Honda CB550K (US imported 1977) bike as my winter project for this year.

Bought unseen (I enjoy the lottery of it) and as was made clear in the advert, it had issues with erratic idle speeds and hanging revs. He’s enlisted your help in some previous posts around 2019/20 but as advertised, the issue is still there.

As it’s not yet winter enough to start the ‘project’, I’d thought I’d give it the first run up today after a week of it sitting in the garage.

Same sh!t, different day. Still hangs and idles at erratic speeds with no real pattern, other than it’s pretty random.

So, airbox off, and I thought I’d have a sneak peak in the entry to the carbs, looking for the obvious throttle bodies out of sync etc and tbh, they are not so far off that you can see by eye. I’ll go thru that procedure later in the week.

Anyway, my main question,,,,

I’m quite familiar with Mikuni’s and therefore more au fait with choke circuits rather than choke flaps.
However, I’ve noticed (and the carbs were still mounted at this time) is that when the choke knob is fully depressed to the OFF position, I can quite easily move the four choke flaps by hand in the region of 20/30 deg. The flaps are also not fully open as I’d probably expect and then I can push the flap down the 20/30 deg that then makes them fully open. There is also quite a bit of play in the linkages between the 1/2 and 3/4 carbs. Possibly a linkage.

So main cause for concern from the observations would be…

- Choke OFF and flaps not horizontal / fully open
- Play in linkages between the different carb choke flaps

Has anyone seen this before? Is it normal? Excuse my ignorance on the Keihins.

I will be dismantling and ultrasonic cleaning etc (also reading some of the guides on here) but just as a first pass it looks a bit suspect to me.

Thanks in advance.

Pics (Not the best) show the flaps with the choke OFF and the flap position.
[ Guests cannot view attachments ] [ Guests cannot view attachments ] [ Guests cannot view attachments ]

badger_eng:
Just an addendum….

My plan tomorrow will be to run the bike without the airbox and just see if the choke flaps are moving independently just to rule out or rule in.

taysidedragon:
The Keihins on my 400f definitely sit horizontal when fully open and all 4 move together. There shouldn't be any flapping about or moving separately.  Those screw heads holding the flaps on look much bulkier than the standard screws too. From memory they are small dome head screws so don't interfere with airflow too much.

badger_eng:
Thanks for the quick reply Gareth. Logic says it’s all wrong but other than logic, I don’t have the Keihin knowledge or experience yet to determine how much it matters.

My fear would be if there is enough free play in the linkage between carbs 1/2 and 3/4 where the butterfly’s could essentially be doing different things as the air is drawn in.
When I run it up tomorrow, I should be able to observe if it runs OK minus the airbox.

If only to settle my mind, it’s probably a worthwhile test.

Once I’ve done that and learned one way or the other, I can move forward with strippage, cleaning and rebuilding / synchro etc.

Cheers

deltarider:
Questions I would ask:
How many miles on the odometer?
Any idea of the owner's history like how many?
How likely is it any previous owner has played with the choke flaps?

Navigation

[0] Message Index

[#] Next page