Topic: Cb550 carburetors

[CB750wanabe]

Hey, everyone. My first post here but have spent some time on the site. I've just recently gotten back into the motorcycle world at 54 years old. I'm in the auto repair business so it's handy for me to tinker with them. I'm looking for a mint clean 1976 CB750. Anyways, my question is: I've just purchased a 1977 CB550 four, that hasn't ran for a number of years. I pulled the carbs. off and went thru them, including the jets that you have to put a little wire through to get cleaned out. She runs great except for when riding, half or full throttle, it just falls flat on it's face as if it runs out of gas. If you pull the choke on, it jumps right up, so I know it goes way lean on fuel. I don't have the boots hooked up from the carbs to the airbox yet and was wondering if anyone thought that this is the cause. Anyone who answers, can atest to the pains taking efforts of hooking this crap back up, so I was leaving them off till I found the problem, or maybe this is the problem. Okay, ralley caps on?? Waiting to here back, and I will be a contributor to this web site in the coming future. Thanks for any idea's in advance, Rod.    Dallas, Texas

[SteveD CB500F]

Running without the airbox will certainly lean it out - just like running with pod filters or velocity stacks.

I guess putting all the gubbins back on is less work than stripping all the carbs again, so give it a go and see if there are still problems with everything stock.  You'll find loads of threads on here that start that way!

[MetalHead550]

Yep you caused a definite lean situation by leaving the boots off.  The air box and filter restrict the air flow to a point that matches what the jets are capable of mixing with to create the right air/fuel mixture.  Just gonna have to put those suckers back on.  An earlier thread mentioned that heating the boots up a bit makes them nice and soft and thus easier to slide the carbs on to.  The best method Ive found is to put the boots in the air box and secure the box to the frame(with the carbs off).  Then with the carbs attached to the intake manifold(not bolted to the engine at this point), angle them downwards so that the manifold is under the studs to which they secure and the thoats of the carbs are at the boots.  Straddle the bike and pull like hell till the carbs pop into the boots, then you can pull them a bit further to get the slack you need to align the holes on the mainifold to the studs on the block.  That probably made no sense, hard to describe.

[TwoTired]

I'll chime in with the airbox and filter adding, in effect, partial choke.
It helps if you take the band clamps off completely for the rear rubber boots, and free the airbox so the air plenum ahead of it moves back to the frame.

Also, the 77 has press in slow jets.  Part of the jet buried in the carb body is a short emulsion tube with cross drilled holes.  These need to be cleaned, too.  Yank the jet straight out, clean and then tap them back into place. 

Did you find the correct float height adjustment?  PD46A carbs should be 14.5mm.  Slide needle in 3rd groove from top.
These adjustments assume stock exhaust system.

Cheers,

[CB750wanabe]

Okay, I'll let everyone know what I come up with. I guess tomorrow I'll work on getting the boots back on as I think everything is clean in the carbs. The way it boggs, it's as if either the same thing is still clogged in each carburetor, which I doubt, or something is effecting all the carbs, as the boots would cause.  Rod

[CB750wanabe]

Okay guys, what everyone thought was right on. I got those boots, finally, installed today and she runs just beautifull. Thanks, Rod...