Cb550 Cylinder 3 Not Firing

[jryftc]

So I just picked up a CB550. Runs real solid, but the third cylinder isn't firing. From what I'm aware of now, it has spark and the points are clean. From here, I should look to replace the third cylinder spark plug, and if not that, just a clogged jet in the third carburetor bowl? Any tips as to not having to pull the carbs to get the jets out? Bike runs and rides fine, starts really quick. Holds idle.

 

[dualitymike]

You can get the jets out just by taking off the float bowl. Four machine screws and it's off. Theres a spring in there that holds in the main jet and braces itself against the bottom of the bowl. The idle jet is long and thin and just screws out. You may have a float that's stuck in the up position and not letting any gas get in there. That would be the first thing I'd check when you get the float bowl off.

 

[xb33bsa]

before you pull the bowl drain it of what gas it bhas into a clean contaiuner look for whater and dirt
how can you say it runs and rides fine if only on three ? that is impossible,if only on 3 it should run slower than a badly tuned 250 with flat tires
and sluggish as fuk ,also should have a difficult time idling unless you raised up the idle speed adjust
is the 3rd header pipe actually not getting hot ?

 

[jryftc]

I've ridden the bike for an hour. It holds idle, and starts on one kick, it just is running sluggish on the three cylinders obviously.The third header pipe is getting hot, but assuming its heat coming from the engine. The muffler is cold. Thanks for carb advice, this is my first time dealing with a 4 carb bike and I dont really feel like pulling these puppies off

 

[xb33bsa]

yeah well next time you light the fires from dead cold observe with your bare hand the suspected dead one if it is not firing it will take a while to even get warm wheras a firing silinder heats up instantly
if the carb has fuel and with a new sparkplug it is still dead then it could be plugged jets or a shorting plug cap,its an old ass bike with original caps buy 4 new ones right away trim the wire a 1/4 when putting new ones on
new plug caps are as number one priority as new sparkplugs
if you have not got the stock airbox on i know a shadetree trick that can clear plugged main jets and it only takes a minute, a plugged pilot jet is pull the bowl time

 

[goldy]

You have probably sorted this out by now, but...start with the simple stuff. If you have spark, then you may have a bad plug/ boot or wire...try changing them. If that doesn't work, check the compression on that cylinder, if it is low the valve adjustment may have gone too tight, a valve might be bent or the piston holed. If all that checks out alright then it's probably a carburetor/ fuel delivery issue. Good luck with it and let us know what you find!

 

[jryftc]

I figured it out. New plug did the trick. Sorry for being an idiot.

 

[goldy]

Glad you got it...and glad it was an easy fix too!