Topic: Number 2 cylinder not firing?

[Inferno333]

Hey guys. Here's my first post on here. And yes it is a question. Haha.

Here's a rundown:
1977 CB550F
069a carbs
#$%*ty pod filters that don't fit well.
IMS out 1.75 turns
4-1 exhaust

It will idle at 2k with no choke after warming up. I noticed the number 2 exhaust pipe isn't getting hot. I think it's just picking up heat from the adjacent pipes. The spark plugs are all pretty new. I need to get a different socket to take them out and check color.

Based on my limited knowledge from reading on here it sounds like I need to pull the carbs off and clean them at the minimum. I would probably just rebuild them since riding season is almost over. Should I just replace the gaskets or do a full rebuild?

Any insight gentleman?

[HondaMan]

Well, here's what I'd do if it were here, in this order:
1. Check for fouled sparkplug. Replace with correct plugs: often the D8EA has been substituted on the 550 bikes, and that should be either a D7EA or the ND (better) equivalent of X22ES-U.
2. Check all the resistances of the sparkplug caps. If, for instance, the ones on #2 and #3 are more than 500 ohms different from each other, the lower-resistance one gets starved for spark (that would be #2, here...). The caps should be 7500 ohms if they are OEM caps (10,000 ohms on post-1975 bikes), with +800 ohms more being their burned-out limit. Replace with 5,000 ohm caps today.
3. Check the O-rings in the castings that hold the carbs to the head. These are old and stiff, and are often cracked. This can make for high idle, poor mixture, and fouled plugs.

[TwoTired]

If, for instance, the ones on #2 and #3 are more than 500 ohms different from each other, the lower-resistance one gets starved for spark (that would be #2, here...).

How do you justify that?  I was taught:
2 and 3 are part of one coil's secondary loop.  Once current flows in the loop, it is the same throughout the loop based on the total resistance that the loop contains and the voltage achieved to create the spark channel conductor.

When the coil's energy field collapses, the voltage rises in the secondary until a spark channel is formed across both gaps.  Since there is no current flowing during the voltage build up, the voltage would be the same at each spark plug, and resistance would not be a factor until current is flowing.

Are you saying the once the spark event begins, the voltage drop causes one plug to shorten it's spark event due to lower voltage?  If so, how could the remaining spark plug sustain an arc without current flowing through the spark plug that no longer has a conductive path through it, as they both are part of the conductive path of the coil secondary circuit?

The caps should be 7500 ohms if they are OEM caps (10,000 ohms on post-1975 bikes), with +800 ohms more being their burned-out limit. Replace with 5,000 ohm caps today.

I've never found anything less than 10K caps on the stock 550's.  And, no Honda documentation that specifies anything other 10K Ω for the plug caps.
5K ohm caps do increase coil heating, and slightly increase the coils power consumption, as they will discharge father toward depletion.  The higher currents will also wear the spark plug's electrodes faster.

I don't understand why 5K caps would be "better", besides being the only ones readily available.

[TwoTired]

The spark plugs are all pretty new.

And it ran well with those for a time?  You still haven't ruled out a fouled spark plug.

Based on my limited knowledge from reading on here it sounds like I need to pull the carbs off and clean them at the minimum.

Any insight gentleman?

Why not just drop the #2 carb bowl unscrew the pilot jet and clean it?  For easier access, remove #1's bowl, too.  Looking inside the bowls will give you a good indicator if the carbs need internal cleaning and removal.

[JDS]

It could also be as simple as no fuel getting to carb #2.  When you drop the bowl make sure there is fuel in there, if not turn the petcock on and see if fuel flows out (put something up there to catch any fuel).  I had the same problem a couple of weeks ago and it was a little crud in the fuel T in the line on that side.  Cleaned it up and it was all good.

[Inferno333]

Fantastic! I knew this was a great forum!

I'm going to pull the plug this week once I buy the appropriate socket. I think they are the D7EA. That's what was  in there when I bought it.

I'll check the carb to make sure it's getting fuel.

I'll start there and report back. Thanks everyone!

[Inferno333]

I finally got a socket that fits the plugs. I pulled each one and found that it had been running pretty rich as there was carbon on each one. The number 2 plug was wet with fuel while the others were dry.

I also found that the number 3 plug was barely hand tight. I'm sure that doesn't help things.

I'll try to fire it up tonight while I'm working on my car and see if anything has changed.

[lucky]

You could have saved yourself time.
Just clip on a timing light to #2 cylinder and see if it is firing or firing evenly.

There is your answer.

[TwoTired]

You could have saved yourself time.
Just clip on a timing light to #2 cylinder and see if it is firing or firing evenly.

There is your answer.

Not so if the spark plug tip has shorted electrodes.  Current will still pass though it and the timing light will trigger each time the plug should fire, but can't.