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Author Topic: 3rd cylinder not firing - troubleshooting the problem  (Read 1665 times)

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Offline Hope

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3rd cylinder not firing - troubleshooting the problem
« on: May 10, 2007, 07:29:43 AM »
Alright, I fired up my '75 CB550, 3rd cylinder header was cool to the touch while the others were hot after about 10 minutes of running.

I will start with the basics, such as pulling the spark plug, and will probably replace it with a new one.

If the spark plug, wire, or coil are not the culprits, where should I look next?
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tmht

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Re: 3rd cylinder not firing - troubleshooting the problem
« Reply #1 on: May 10, 2007, 07:35:52 AM »
Quote from: Hope on May 10, 2007, 07:29:43 AM
Alright, I fired up my '75 CB550, 3rd cylinder header was cool to the touch while the others were hot after about 10 minutes of running.

I will start with the basics, such as pulling the spark plug, and will probably replace it with a new one.

If the spark plug, wire, or coil are not the culprits, where should I look next?

Fuel delivery. Check the pilot jet, emulsion tube and main jet. Inspect the floats for proper operation and adjustment.
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Offline TwoTired

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Re: 3rd cylinder not firing - troubleshooting the problem
« Reply #2 on: May 10, 2007, 12:00:07 PM »
X2 on tmht's list.

Less likely but maybe...  When's the last time the tappets were adjusted/inspected?  If, for axample you lost an adjuster nut on #3, the cylinder may not be able to work right.
This is faster to check than the carb stuff, just open up an inspection cap or two.  If OK, move on.

Cheers,
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

tmht

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Re: 3rd cylinder not firing - troubleshooting the problem
« Reply #3 on: May 10, 2007, 12:14:06 PM »
I am sure TT can verify this... Also if your bike has the style of floats that are hollow in the inside, check them for holes. A friend of mine is working on a DOHC 750 that has those style of float and one had a hole in it. The float filled with gas and didn't well, float, thus not letting any gas in.
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Offline TwoTired

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Re: 3rd cylinder not firing - troubleshooting the problem
« Reply #4 on: May 10, 2007, 12:55:38 PM »
I don't know of any Cb550s that had brass floats.  I've only seen the solid plastic type that have the tiny air pockets molded in.

The 75 550 has individual bowl drains.  You can catch and measure what drains out of each one.  The quantities should be the same on each of the four.  If not, you have a float issue of some kind.  And, you can also check for fuel contamination this way, as well.  The idle jets are only 0.016 in. diameter.  You find bits bigger than this in the drainage, and they will stop fuel flow through them.

Cheers,
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Snowdigger69

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Re: 3rd cylinder not firing - troubleshooting the problem
« Reply #5 on: May 10, 2007, 01:48:04 PM »
I had the same problem. Bad wire on that cylinder, had spare coils and wires, replaced and problem was solved. For what it's worth.
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