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Strange spark plug test result

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exvalvesetdabbler:
When the rebore was done, were the valves checked and also clearances set properly upon re assembly.?

To soot up plugs it's either getting way too much fuel or burning something else to create the soot. If it's not firing it would be blowing out fuel from the exhaust, ie smell of petrol.

All choke flaps opening properly?
Float heights correct?
Compression on each cylinder?

Does the no.2 header pipe feel cooler than the others after a short fire up?

Just as a side note, your spark may look to  be a bit weaker when cranking on the starter because the battery voltage drops, pull the lead of 1 or 4 and test the same suspect plug on the other  coil.

 Other than that I would be looking to see if fuel is getting  past the o ring on the main jet.

Regards
Dave

K2-K6:
Swap the #2 plug with #3 .... then run it to assess.

Both of those plugs run on the same coil .... if the problem remains where it started ... likely the carb is next suspect. That's assuming you already swapped  2&3 plug leads with nil effect ?

Athame57:

--- Quote from: exvalvesetdabbler on October 04, 2025, 03:36:10 PM ---When the rebore was done, were the valves checked and also clearances set properly upon re assembly.?

--- End quote ---
I had a different garage do those at the same time as I had them fit the header pipe properly. Bike was great for a day and now this. I expect I'll be heaving the carbs out.  ::)

McCabe-Thiele (Ted):
That diagram is all wrong.

As you sit astride the bike Cylinder 1 is on the far outer left, then its cylinders ,2,3,4.

Ken4004:
I had the same issue last week one cylinder not firing turned out to be the carb putting too much fuel into the piston so carbs out and changes the float fuel valve that wasn’t closing properly and flooding the carb.
After replacing valve and reassembly started up with no issues.

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