Topic: CB750 Carbs on a CB550

[Rocketman]

Considering CB750 PD42 carbs on my CB550 track bike.  The motor has 61mm pistons at 10.5:1, 358b Webcam, mild porting with +1mm valves.  Welcome any thoughts or suggestions.  Does anyone know the difference in the CB550 intake manifolds used through 76 and those from 77 (K3) on?  The 550 carbs are 75mm on center while the 750 carbs are 76mm/80mm/76mm.  Any suggestions on rubber tubes connecting the carbs to the intake manifolds?  There are a number of references to using 750 carbs on 550's in the forum, but little detail.  Have any members tried this combination?  As always, thanks.

[Bill/BentON Racing]

PM Greggo,he's got some we made back in '77! Bill nothing special,but works,maybe I can find pics later. I used 69 4-1 carbs, they work well!!

[spdygnzlz]

I mounted a set of early 750 carbs on my 550/650 hybrid motor.  They mounted using the stock 650 rubbers.  It's still being built so I can't say anything about how it runs but in order to fit it, I had to modify the throttle cable stop to clear the 650 head (a bit taller and bulkier than the 550's) and also mod the tank to clear the linkage movement.  Also had issues clearing the petcock which I still haven't addressed.  Probably going to try a less bulky alternative at some point but I've been so busy with work the bike has sat under a moving blanket for a few weeks.