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CB550 Cylinder 1&2 not firing

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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:

--- Quote from: deltarider on April 12, 2024, 11:30:36 AM ---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.

--- End quote ---
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. ;D
Plugcaps always have been and are the CB500/550 Achilles' heel.

Robert W:
Since governments have mandated alcohol petrol blends, we have a problem. How could they is another question. Ethanol will deteriorate everything that was not made with this compatibility in mind. it basically eats rubber, plastic, fiberglass, etc. Carb 1+2 fed from line 1 and carb 3+4 fed from line 2 both from the dual outlet petcock. I suspect you have little rubber bits blocking the idle jet, which is a lot smaller orifice than the main jet.

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