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CB550 Cylinder 1&2 not firing

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Mike_Berkshire:

--- Quote from: K2-K6 on April 11, 2024, 08:17:24 PM ---One coil only runs cylinders 1 & 4 with the other coil running the 2 & 3 pair.

Easy to quick check, no numbers needed.

Another easy test, if you've any e-z-start or brake cleaner, you can put a little squirt into the cylinder via it's sync port while its running to see if that pot will chime in, obviously then indicates fuel absent on that one.

--- End quote ---
Thanks - Ill try the easy start tomorrow & i'll check the coil connected to #4 is also connected to #1 and the coil connected to #3 is connected to #2

Bryanj:
The other possibility if ht leads are correct is kinked fuel pipe to 1&2 or a blocked tap outlet to 1&4

Mike_Berkshire:

--- Quote from: Bryanj on April 11, 2024, 08:58:32 PM ---The other possibility if ht leads are correct is kinked fuel pipe to 1&2 or a blocked tap outlet to 1&4

--- End quote ---
Thanks! As the float bowls are filling I would have thought the fuel supply is good but I will probably need to get the carbs off tomorrow and can check fuel lines are clear and not kinked & I have some new 5.5mm dia fuel line I can use. To me the fact that the 2 failing cylinders are fed by the same fuel line suggests that the fault is linked. I blew out all fuelways and jets etc before reassembly but its possible there was some crud in the 1&2 fuel line that flushed through to the float needles or jets and clogged them. EZ start will be a good indicator.

deltarider:
Your remarks are contradictory. You say the floatbowls fill up and you don't rule out you've kinked lines.
If you're unsure, I'd begin by tapping (gently) the floatbowls with the stub end of a screwdriver to activate sticking float needles and/or remove dirt in between the floatvalves and their needles. Often this is all what it takes.
If you're sure the floatbowls do fill up, this is what I'd do.
Do a start attempt and then check the #1 and #2 sparkplugs. If the plugs noses are dry, fuel does not arrive. If the plug noses are wet, fuel does arrive and the problem is elsewhere.
If the fuel does not arrive, I'd leave the carbs where they are.
Unscrew the airscrews from the sides of the affected carbs (after writing down the position they were in) and spray carb cleaner using a straw in the openings and hope it will clean the slow jets. Reposition the airscrews and start engine. Maybe the carb cleaner has cleared the slow jets. I had success with this once.
If not. On a CB550 LH side I find it not difficult to just unscrew the floatbowls with the carbs in situ and then remove their jets for inspection. Long time ago I have replaced the 4 crossheads of every floatbowl by allen. Much easier. All maintenance/cleaning on these oldstyle carbs can be done with carbs in situ. It helps if you're familiar with what's inside though.

Mike_Berkshire:

--- Quote from: deltarider on April 11, 2024, 10:19:43 PM ---Your remarks are contradictory. You say the floatbowls fill up and you don't rule out you've kinked lines.
If you're unsure, I'd begin by tapping (gently) the floatbowls with the stub end of a screwdriver to activate sticking float needles and/or remove dirt in between the floatvalves and their needles. Often this is all what it takes.
If you're sure the floatbowls do fill up, this is what I'd do.
Do a start attempt and then check the #1 and #2 sparkplugs. If the plugs noses are dry, fuel does not arrive. If the plug noses are wet, fuel does arrive and the problem is elsewhere.
If the fuel does not arrive, I'd leave the carbs where they are.
Unscrew the airscrews from the sides of the affected carbs (after writing down the position they were in) and spray carb cleaner using a straw in the openings and hope it will clean the slow jets. Reposition the airscrews and start engine. Maybe the carb cleaner has cleared the slow jets. I had success with this once.
If not. On a CB550 LH side I find it not difficult to just unscrew the floatbowls with the carbs in situ and then remove their jets for inspection. Long time ago I have replaced the 4 crossheads of every floatbowl by allen. Much easier. All maintenance/cleaning on these oldstyle carbs can be done with carbs in situ. It helps if you're familiar with what's inside though.

--- End quote ---
Thanks, a good point re the fuel lines. I have completely rebuilt the carbs so pretty familiar with whats inside and I did replace the JIS crossheads with allen screws so that should make things easier. I will go through the steps again today with more care as I was a bit rushed last night & may have missed something.

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