Which Carbs do I need?

[Acro1985]

Hi All

I am new to the SOHC scene having just bought a 1977 CB550 project to get my teeth into. the bike unfortunately didn't come with the right carbs, they appear to be from a CB400. from doing some research on the forum it would appear my frame is a CB550F2 from the vin on the headstock but the engine number (CB550E-2028203) is from a K3 I believe.

So I am after some help/advice as to which carbs I need to track down.

[McCabe-Thiele (Ted)]

If you look at the carbs you will see the type number on the top outer flange by the mounting bracket on number four carb. They will all be stamped there they should be 637B on a 500. The 550 Carbs are marked 069A

You can fit 550 carbs if you swap the jets onto a 500 - I doubt the 400 ones would fit easily they are type 054A.

[Bryanj]

Engine makes no difference but inlet manifolds do, are there screws on the inlet manifolds for vac balancing

[Acro1985]

The carbs I have are stamped with 054A, i have offered them up to the inlet manifolds on the engine and they fit/marry up to the inlet openings at all.

there aren't any screws on the inlet manifolds for balancing.

thank you for your responses.

[McCabe-Thiele (Ted)]

They are the same carb body number as my 400 carbs.

[Bryanj]

If no screws on manifolds they are 550 K3 manifolds which use PD(devil) carbs with a different plenum and rubbers to carbs.
If you have to replace i personally would go for a complete 500 stup from filter box to head

[Acro1985]

Thanks for help.

I am right in thinking the PD (devil) carbs are so called devils because they are a nightmare??

as I need the air box too I will have a look for a 500 setup, is there a specific carb number to look for.

[Bryanj]

Correct, PD carbs are a total nightmare, especially if not cared for, you need any 500, except K3 which is rare in uk or a US 550 K0,1 or 2

[McCabe-Thiele (Ted)]

Correct, PD carbs are a total nightmare, especially if not cared for, you need any 500, except K3 which is rare in uk or a US 550 K0,1 or 2

I am confused as my 400 carbs are definitely 054A  I have ckecked them - did they use that number on the PD type or is it the manifolds that are for the PD type carbs here?

Might be worth checking the parts numbers for K1 & K2 that should be in the site downloads section.
My 500 has a K1 engine fitted with 550 type 069A carbs.

[Nurse Julie]

Welcome to the forum.
Do you have a photo of your bike and is it a UK model or a USA import?

[McCabe-Thiele (Ted)]

Looks like the part numbers for K1 & K2 are the same so you will be looking for a set of  069A carbs with the correct manifold.

I consider myself a novice so you need to get confirmation from Bryan or others - I guess you should be able to tap holes in your existing manifold for the Vac points.

[Acro1985]

Hi Nurse Julie

the bike came in bits so I haven't taken any photos yet, but if you let know which parts would help I will happy up load some.

As far as I am aware its a UK bike, but I am basing that of the HPI report which has it down as first being registered in the UK on the 4th August 1977, still waiting for the V5 to come. 

[mickwinf]

Ted its not as simple as tapping a thread as the k3 manifolds are a different length.

[McCabe-Thiele (Ted)]

Ted its not as simple as tapping a thread as the k3 manifolds are a different length.

Ah so it needs a mainifold plus a set of carbs on the correct bracket - then the air box as well presumably.
Is a K3 the same frame dimensions for fitting it all?

These look like the manifolds as they have vacuum screws or is the 550 different spacing to the 550?
.https://www.ebay.co.uk/itm/355880080705?fits=UKM_Make%3AHonda&itmmeta=01J4MC7DQ8PQ5B4APFDWJ0DW1Q&hash=item52dc1b1541:g:mhsAAOSw9UdmmNT~

[Seabeowner]

That's not a bad price for the 500/550 manifolds with the balancing ports.
Get 069A carbs if you can. Or if not 627b or 022A (but these may need jet changes)
As said F2 engine is the same as a K3.