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No2 Cylinder High Vacuum.

Posted: Wed Mar 17, 2021 10:50 am
by Tdibs
Hello,

I am having some trouble with my 99 Xj600N

Symptoms are rough sounding idle, hanging revs at idle when warm - sticks at 2-3k at traffic lights for 10 seconds, then drops back down to 1.3k idle. Pulls fine throughout all the rest of the throttle range as far as I can tell.

Putting on sync gauge, no2 cylinder is stuck pulling huge vaccum, all other cylinders respond to adjustment, no 2 shoots up and will not move.

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Also noted, putting my finger over these holes on 1,3,4 carbs kills the mixture, covering these holes on no2 (problem cylinder) makes no difference.

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Any smoking guns to check first? Ive pulled the carbs twice and been through them, I cant find anything obvious, all air passages I can blow compressed air through etc, Pilot is spotless. I could not find any tears in intake boots either. Mixture screws are still blanked off from factory, spark plugs show similar mixture across all 4.

As I understand it, No2 is the master carb, should I just adjust everything up towards that? or should it not be roughly pulling the same vacuum as others when idling?


Cheers!