CB550 Cylinder 1&2 not firing

[Mike_Berkshire]

Hi, thanks for all the help re Carb rebuild for my CB550. I was dead chuffed when i put the rebuilt carbs on the bike and it ran. However, I have quickly realised that the pipes for cylinders 1&2 are cold & therefore not running on these cylinders. My logic is that as 3&4 are running its not condensers, not coils, not plugs (there is a spark on 1&2) and not fuel to the carbs as the float bowls are filling. What im guessing is that there was some contamination in the fuel line to the carbs for 1&2 that has blocked the jets. Tomorrow im planning to remove the carbs, clean them, blow out the jets, check float valves, float needles etc and try again. Is there anything obvious that anyone can think Im missing? As I sit on the bike I am numbering the carbs from left to right from the gearlever side. Cheers, Mike

[Johnny4428]

Sounds like fuel issue alright. Electrical delivers to 1&4 and 2&3 cylinders of course.

[McCabe-Thiele (Ted)]

Are the plug leads in the right order could 1 & 2 be back to front?

[Mike_Berkshire]

Are the plug leads in the right order could 1 & 2 be back to front?

Interesting. I guess its possible. Each of the plug leads is numbered and the leads go to the correct cylinders according to the numbers so I think its unlikely but how do I check the numbers havent been put on the wrong leads or moved as an act of humour by a previous owner or their mate playing a wizard wheeze?

[K2-K6]

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.

[Mike_Berkshire]

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.

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]

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

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]

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.

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.

[deltarider]

The tube to the T-joint 1+2 should be 17 or 18cm long, depending of the model petcock your Cb550 has. The oldstyle petcock with the bowl requires a length of 18cm, the newer type 17cm. Ideal ID is 5,5mm.
After a long period of sitting you can expect irregularities. When carbs have been drained for a long period, O-rings at the T-joints will shrink and so - possibly - cause initial leaking. Usually the rubbers will regain their original dimensions, but I prefer to keep my carbs in a natural state, which is wet.
As far as problems with the floats, both valves and needles, tapping (gently!) the floatbowls with the stub end of a screwdriver can do miracles. Flushing the floatchambers by removing the drainscrews and then opening and closing the petcock can also help, or both methods combined.
Make sure the joined vent tube for carbs #1 and #2 is free and can vent to the open.

[Mike_Berkshire]

The tube to the T-joint 1+2 should be 17 or 18cm long, depending of the model petcock your Cb550 has. The oldstyle petcock with the bowl requires a length of 18cm, the newer type 17cm. Ideal ID is 5,5mm.
After a long period of sitting you can expect irregularities. When carbs have been drained for a long period, O-rings at the T-joints will shrink and so - possibly - cause initial leaking. Usually the rubbers will regain their original dimensions, but I prefer to keep my carbs in a natural state, which is wet.
As far as problems with the floats, both valves and needles, tapping (gently!) the floatbowls with the stub end of a screwdriver can do miracles. Flushing the floatchambers by removing the drainscrews and then opening and closing the petcock can also help, or both methods combined.
Make sure the joined vent tube for carbs #1 and #2 is free and can vent to the open.

Thanks for all the advice - the problem turned out to be more basic than I thought. I noticed, with a fresh pair of eyes this morning, that the spark on 1&2 was not at the electrode but intermittently in the plug body. New plugs and its now firing on all 4. I wouldnt say its running smoothly but given that as soon as I have the bike registered Im going to totally strip it down, its good enough to convince me that there isnt anything seriously wrong with the engine which is good to know. All O rings in the carbs are new Viton seals as are the the ones on the fuel lines. I have some new 5.5mm dia Pearl fuel line I will fit when I put the bike back together again and will strip, properly clean and refurbish the petcock too. 

[Johnny4428]

Glad you have got it firing on all 4 now Mike, just a bit of fettling to get it running like a Swiss watch.

[deltarider]

Aha, so it's just nother case where a fuel problem turns out to be electrical.
Plugcaps always have been and are the CB500/550 Achilles' heel.