Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Mototech on June 25, 2021, 05:34:43 PM
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I have an odd misfire on cylinder 1, at idle & smallish throttle, it sounds like it isn't really running, with the odd chuff thrown in. I have checked ignition coil resistances & all appears to be ok, new plug caps & plugs, but still there. I also replaced the needle jets & needles as there was wear evident, anyone have any more ideas?
I should also say, compression good & consistent on all cylinders & electromic ignition just fittted, but the issue is exactly as it was before I started!
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If you tilt the bike from side to side with the engine running, does it start firing on all 4?
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Stating the obvious - if its only a mis on 1 cylinder, its got to be that cyl HT circuit, that cylinders carb/inlet -
maybe sounds like float height/float valves (think thats what Julie might be getting at)
What model? HT lead in good order?standard airbox or pods? exhaust? Any recent rebuild/adjustments?
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Stating the obvious - if its only a mis on 1 cylinder, its got to be that cyl HT circuit, that cylinders carb/inlet -
maybe sounds like float height/float valves (think thats what Julie might be getting at)
What model? HT lead in good order?standard airbox or pods? exhaust? Any recent rebuild/adjustments?
As 1 & 4 share a coil, I would have thought the misfire would have effected
It is 1977, all as it left the factory, I have stripped & rebuilt the carbs with new needles & needle jets & fitted electronic ignition, symptom is the same as before.
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With electronic ignition fitted you must only have resistor spark plugs OR resistor plug caps fitted but NOT both.
If you have both fitted then it's possible the plug leads will short across to the cam cover and earth on cylinders 1 or 4.
Hope this helps.
Skoti
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Stating the obvious - if its only a mis on 1 cylinder, its got to be that cyl HT circuit, that cylinders carb/inlet -
maybe sounds like float height/float valves (think thats what Julie might be getting at)
What model? HT lead in good order?standard airbox or pods? exhaust? Any recent rebuild/adjustments?
As 1 & 4 share a coil, I would have thought the misfire would have effected
It is 1977, all as it left the factory, I have stripped & rebuilt the carbs with new needles & needle jets & fitted electronic ignition, symptom is the same as before.
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Just because you have stripped carbs and fitted some new bits, that doesn't guarantee its not a fuel problem.
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If you wind the air screw for idle mixture in and out one carb #1 while it's running you should get a response as the mixture changes, between 1/2 and 3 turns out should give a good range that you can clearly hear in cylinder running.
If it doesn't do this in changing response, then there's the likelihood of that idle circuit being impaired.
Also run it in the dark and look carefully for leak sparks from that #1 lead to see if there's any compromise there. They can leak out to the rocker cover on the way to plug where it's nearest.