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Mystery misfire

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Mototech:
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!

Nurse Julie:
If you tilt the bike from side to side with the engine running, does it start firing on all 4?

philward:
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?

Mototech:

--- Quote from: philward on June 25, 2021, 05:57:56 PM ---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?

--- End quote ---

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.

Skoti:
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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