Topic: Carburetor Question

[denone]

I have a 1974 CB550. Will carbs from a 77 or 78 CB550 bolt straight on, or do I need to change anything, jets...etc ? thanks

[MetalHead550]

The carbs from a 78 are different from those on a 74 but I dont see why they wouldnt work just fine.  Only "problem" I can think of would be the choke mechanisms and linkage are different as well.  The 74 didnt open the throttle with the choke and the choke lever was right on the carbs while the 78 did open the throttle enough to idle on its own and the choke lever or whatever you wanna call it was up by the gauges.  The push pull throttle cables may be a different length as well.

[migopod]

The intake manifolds are slightly different as well.  I think the 78 carbs are spaced slightly further apart.
Also with the newer carbs and fitting manifold the stock airbox may not fit without modification.
The push/pull cables are different lengths and you will need a choke cable, and finally the 78 carbs
will have one fuel line instead of two.

[TwoTired]

I concur with what migopod said about fit.  But, you asked about jetting, too.  Jetting for the 77-78 CB550K is matched to the inlet air flow and exhaust pipe/muffler flow characteristics.  If you also moved these parts onto your 74, you'd be good to go.  But, there are frame changes and mount locations that are different for these components.

Without rejetting the carb for induction and exhaust allowances, you may have flat spots at certain throttle positions, restricted top end power, plug fouling, etc.

Tuning carbs to modified bikes can be fun, rewarding, and greatly increase knowledge about these bikes and engines in general.  But, you'll likely be dissappointed if you're just looking for a quick, cheap fix.

[Flood]

I have a '76 550F and installed a cheap '78 engine while the original one is on the bench. yes, the intake manifolds are slightly different and don't fit on the engine.

I didn't get the '78 carbs I have to fit the in the frame. Then there's the handlebar-activated choke. In the end I squeezed the '76 carbs on the '78 intakes.

I don't know if it's possible with enough work put into it- probably.

But to answer your question (will it be a straight bolt-on?): no.

Cheers, Remi