Honda CB 550 Carb Rebuild: UPDATE

Ripped carb boot

I got the carbs for my Honda CB 550 K all nice and clean (or so I thought), and back on the bike.  Man, the difference in how they looked, made me think I would fire the bike up, and they would be humming along….

It wasn’t in the cards.  The first problem was, when I removed the carbs from the bike, the “boots” that connect the carbs to the air box were ripped.  This can cause air induction leaks, and make getting the sync near impossible.  So, after getting them all in order, I put them back on the bike, with a set of pods.  Pods are the small, individual air filters, which seem to be very popular with the cafe racer crowd.  I have to admit, they look pretty cool, but everything I have read about them, has led me to believe that they are far more of a hassle to get tuned right, with rejetting required, to compensate for the decreased air restriction.  I had them on there simply to eliminate dirt and debris from blowing into the carbs, while I tried to get them synced.  I immediately bought a used set of boots, and impatiently awaited the delivery.

Knowing that the sync would not be perfect, I still wanted to get the carbs back on the bike to see if they worked.  Before this rebuild, I had never taken carbs completely apart, stripping them to down to the smallest parts, and cleaning them.  So I was a little nervous when I fired them up for the first time.  But they DID work.  The engine turned over, and although there was some sputtering (possibly from the oil and other products I had put into the tank for cleaning), it ran roughly on its own steam for a bit.  I let it idle, only to find that the #4 cylinder was not firing correctly.  The tell-tale sign of that header being cooler than the others, led me to believe that I needed to get back into the carbs, and see what was blocking fuel flow.

Once again I removed the carbs.  This time, instead of having to wiggle the carbs free of the air box and boots, the pods came off in a snap, and I now saw the upside, to the use of these things.  I opened carb #4, and low and behold, a clogged slow (pilot) jet.  How this ended up with dirt in, after the toxic baths I gave it, is beyond me.  But I cleaned it up, and proceeded to put it all back together again.

Back on the bike in minutes (these pods are really growing on me), and fired back up.  Header #4 is now getting just as hot as the others, but the idle is hanging.  It seems fine if I don’t touch the throttle, but the minute I touch it, the RPMs hang at 3000.  Not good. I got some advice from the SOHC-4 forum, and checked the throttle cables.  They were on too tight, causing the throttle not to snap back as quickly as it should.  While this was an important fix, it was not a remedy for the high RPM.

CB550 set up for carb sync

I decided to do the carb sync anyway, just to see where I was at, and if this helped with the hanging idle.  I set up for the sync, and got them all nice and even.  Unfortunately, this did not solve the problem.  But it was one more thing checked off the list.  I had also checked and adjusted the valve tappets, to make sure the valves were in the right position at the right time, when the cylinders are firing.  also, ignition timing was checked and adjusted, with new points and condensers replacing the old ones I had on there.  All these things are necessary for a 3000 mile tune-up, but none of them fixed the idle issue.

Looks like I’m going back into the carbs.  Could carb slides be hanging up after repeated cleaning?  Could the new throttle spring I put on not be snapping back enough?  Are the float levels off?  All things I will address today, while the temp keeps low, at a pleasant 90 degrees.  The past two days have hovered around 100, and that has taken its toll on my ability to work methodically.  Back to the grind…

You can see more about the Honda CB550 rebuild HERE:

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