Topic: '77 vs '78 Keihin PD Carbs

[neudl]

I have a '77 CB550K, with an engine from a '72 CB500.  It's got the Keihin carbs from the '77, and I'm looking for a spare set.  Are the '78 carbs the same?

[TwoTired]

Both 77 and 78 Cb550Ks had PD carbs,  They have the same castings.  With some internal set up changes.
77 CB550F carbs are different style and use the same mountings as earlier 500s and 550s.

What carbs do you have?  Do they have PD cast into the bodies?

Cheers,

[neudl]

They do have PD stamped in them, and have 90 mains and 42 slow jets, which I'm guessing makes them '78.  I just picked up an identical set as spares.  My bike has stock air box and 4-4 exhaust from the '77 550.  Only the engine was swapped in from the CB500 by a previous owner.  I've never really thought about the performance issues of using the PD carbs on a 500 engine, and its never run either too rich or lean.  Any thoughts on whether I'll need to change the jets?

[TwoTired]

There was a European CB500 K3 with PD style carbs, according to the shop manual.  They had a smaller air jet (#120 instead of #130), different slide needles profiles with a different setting and the #42 slow jet.  They still had #90 mains.  (See pg 178 of the  Honda shop manual.)  I've no idea if they were stamped with the 46 and a letter for the set up config.

It does make sense that with the lower displacement, the engine would suck a bit less on the carbs, necessitating a fuel metering change of some sort.  I've no direct experience with your set up, though.

Cheers,

[neudl]

Thanks for the info, your knowlede of all things SOHC never ceases to amaze.