KZ750 Dead Cylinder & Backfiring Out Carbs

BACKFIRE

Imo, the carbs are unrelated to backfire issue.

Imo, condition and fitment of advancer is the likely cause of backfire issue (especially given no leaking intake valve, good compression, and proper cam timing).

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LACK OF COMBUSTION

Lack of combustion in one cylinder is likely due to ignition timing issue or fuel mixture issue (not spark quality or compression issues already ruled out in this case).

Regarding fuel mixture --- was correct service fuel level assured by checking with the clear plastic tube test (the only reliable test imo)?

And suspicion continues as to possible problem in carb pilot circuit causing overly rich mixture.

Another more remote possibility could be a spark plug that fires well when viewed outside the cylinder, but doesn't fire properly under compression when screwed into the head. Could install a new sparkplug, just in case.

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After resolving the faulty advancer issue, would assure correct ignition timing and proper advancer function by using a strobe type timing light. All before further addressing carbs.

Good Luck!

Yes, I am now convinced that the backfiring was entirely this advancer problem, and pin problem... I also think I have bad valve timing because of the shifting around the advancer did (advancer has the timing marks on it that I used to set cam timing.)

Yes, the float levels were checked twice, as mentioned, and are spot on. There may be other issues with the carbs; they are off right now anyway, and I have lots of time to clean them a 4th time...

I have tried switching the plugs around, as mentioned, there was no difference.

Right now I am betting that 80% of my issues were caused by the timing being off.

WBPDX wrote:

... the float levels were checked twice, as mentioned, and are spot on....

Hoping this means tested via clear tube method to assure correct service fuel level in float bowl. Because the method of "measuring with carbs upside down on bench" is unreliable with these old carbs.

Good Luck!

Yes, clear tube method. I realise measuring float sag is completely worthless. It's also more work than the clear tube method!