Topic: Cylinder STILL Not Firing

[mrfish2]

Took my CB550 out for her maiden voyage today and all was well for about ten miles, then she started acting like there was a vacuum leak again (the revs would hang up around 3k) and died at every stoplight I came to if I didn't blip the throttle while idling. Got her home and discovered the #4 exhaust header was almost cold enough to touch (this being after a ~30 minute ride).

After doing some research it seems most likely that I'm either getting no fuel or no spark to that particular cylinder. Would this also cause it to sputter and die while idling?

[flybox1]

Be sure....for starters....
You're getting fuel to the bowl
Your pilot jet has not fallen out
You have good spark ...which includes the correct plugs, good plug gap, a good plug cap and wire

[C5paul]

As you might know, your #1 and #4 cylinders share a coil to provide spark.

Electricity flows down one coil post, through your engine, and up the other post. That usually means if one quits sparking so does the other. However, a fouled spark plug can provide an electrical path with little to no spark. That could allow your #1 to fire while the #4 struggles to ignite fuel.

I have a few suggestions:

Remove #1 and #4 sparkplugs. Be sure they are grounded to your engine. Have someone crank over the engine while comparing spark on both plugs. Is one significantly brighter? (remember they are not under compression so this is just a basic test...not Gospel).

If you have the fittings, check the float level on the #4 carb. A low level will cause a lean condition that could cause your temperature difference. I would be more inclined to look into carburetion issues since you said the idle hangs (a lean condition certainly tends to cause this over an ignition failure).

I am sure plenty of suggestions will come after mine. Start with basics. I personally would make a quick spark check and go directly to the carb (or intake leak as you stated).

Best of luck sir.

[Vinhead1957]

Measure your plug cap for #4.   

[mrfish2]

Thanks for the suggestions guys, but still, would not firing on one cylinder cause it to sputter and die at idle? I'm about to go tinker with it and figure out what's wrong.

[mrfish2]

I fixed the issue!

It ended up being the float valve, and now the #4 is just as hot at the rest of them. Still, it won't idle.  After the engine cools off I'm gonna check the tappet clearences again to be sure, but this is starting to sound like a vacuum leak issue (the revs keep hanging up around 3k, it loves to misfire, and has no power climbing hills) and I can't find it anywhere around the carb boots. The only other place I know to check is the o-rings inside the intake manifolds, but that means taking the carbs off again. Yay! My favorite activity...........

[mrfish2]

Well I was wrong, it wasn't the float valve. I did adjust the tappet clearences and reset the timing again, and took the carb rack off the bike and checked the o-rings behind the intake manifolds which ended up being perfectly fine. I replaced the floats in the #4 carb with OEM from Honda (that put a hurtin on my wallet) along with new feul line and cleaning the rack again while I had it off the bike.

Put the rack back on today and the damn cylinder STILL won't fire. Checked the plug and it has a lot of carbon build up on it, and wouldn't spark at all while my buddy kicked it over. Pretty sure it's fouled. I want to replace the plug caps, but after doing a lot of research around here I can't determine exactly which caps I need. Help?

EDIT: Checked the resistance on the #4 cap and it held steady at 9.5k ohms