Topic: CB550 breaking up around 5500

[Blackhole]

I have a 77CB550F with what I believe to be a 74 550K motor.  It starts right up and runs good until you get to 5500 rpms then it starts breaking up.  You can't get much out of it at that point.  I will have my speedo done this next week but I don't think you could get it to do 75 mph the way it is now.   It has pods on it with a 4 into 1 header.  The main jets are 100s and the slows are 38s.  I was thinking I needed to go a little bigger on the mains but when I pulled the plugs they look like the bike has been running rich.  It has Keihin carbs on it but I don't know how to tell what model or size they are.  The number on the motor is 1036780.  The problem is I bought the bike with another parts bike and they were both in boxes so I am not sure what year the parts are.  This is a picture of one of the plugs.  How do I tell what carbs I have?  I cleaned the carbs, set the floats and replaced the mains and slows.  The timing is set and the advancer is working.  It also has a Dyna s ignition.  Any Ideas as to what would be causing this ?  Thanks for the help.

[bjbuchanan]

There will be a 4 digit i/d stamped in to the carb body, like for instance 657a on your bike. On the rack side of the carbs, not the airbox side of them.

What I would do is worry less about rpm and pay more attention to throttle positioning at these issues. Air screw is idle, pilot is off idle to ~1/4 ish, needle begins working in that range too. With the pods you gotta step up usually two steps on main and pilot and bump the needle clip to a position richer. For instance on a 750 it would be something like 42/45 pilot and 125~ main and the needle clip on the 4th slot from top. Compare to stock which is usually 40 pilot, 110 main and middle needle clip slot.

Sure it doesn't just equate exactly or transfer right over but it is a direction. There are guys running pods on your size bike and have got it all sorted out, use the search function it is your friend
http://forums.sohc4.net/index.php?topic=116480.0

That is a thread with the i.d. info in it, good go to stuff. Just remember to that if you are trying to do plug chops that you gotta really focus on keeping the bike in that throttle travel range for the chop for at least some time to get it to color up. Idleing around and then a quick buzz to half throttle or something isn't really gonna do much and will probably just still be idle colored, just a thought

[zeech]

Having the same issue with a 74 CB550 running K&Ns and 4-1 Exhaust. My plugs look just like those, all gunked up.

Jets are 135s right now and I'm moving down to 110s. I think I need have the carb adjusted more as well, we'll see after the 110s how it runs.

[Blackhole]

The number on the carbs is 627B and the needles are set in the center groove.  Would you change the mains to 110s and raise the needles up one or two, or should I just move the needle position first?  Looks like these are CB500 carbs. Thanks

[Blackhole]

It is fixed !  I put 110s in for mains and 40s in for the idle jets along with raising the needles two slots.  Took it out for a test run and it ran worse.  When I was removing the pods to start over with the carbs I looked them over and there it was.  The pods are cheap Chinese parts and are reduced down to one inch from an inch and a half.  I took them off and went for a ride and what a difference.  When the motor got up to 5000 it just could not get the air it needed.  I put the mains back to 100 and dropped the needles down one and it even ran better.  I just need to get a good set of pods or buy an air box.  Thanks for the help.