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one exhaust header cooler than the others - Ideas?

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    one exhaust header cooler than the others - Ideas?

    On the 81750L - Cyl 4 header is cooler by about 30 deg than the other 3 (180F vs 210F). I'm thinking its running richer than the others (though could be something totally different) and want to ask ya'll before diving into it. 'Cause I'm trying ANYTHING else before cleaning the carbs AGAIN and frankly will live with this difference if there is nothing else to check other than tearing down the carbs AGAIN. Below are some thoughts and the history.

    - Potential causes?
    rich
    spark plug issue

    - Potential solutions?
    balance carbs

    - History
    Carbs fully (ultrasonic etc.) clean over winter. Ran well. Sat on sidestand for months. Discovered - now fixed - leaking petcock (and float likely - not yet confirmed) as it seemed that the oil had gas in it. That has been repaired and oil changed. After the repair, Cyl4 did not fire while engine was running. It may have fired in choke mode though I did not verify.

    I blew out the cab while on the bike by taking off the top cover and taking out the spring and cylinder/pin and removed the bowl and the main jet and rubber plug and the drop-in brass thing with the 8 holes that the main jet screws into and pin goes up/down in. I used compressed air to pressure blow all the orifices. After this, the bike runs excellent, idles at the point set prior to sitting those months and engine runs extremely well except for this cooler exhaust header.

    Thoughts?
    1981 GS750L - Owned since 1990 when graduated high school and since have been discovering all the things not disclosed by seller.
    1983 GS750E - bought in 2016 as a rough runner to use while rebuilding 81L and then to combine with ES to make one good one
    1983 GS750ES - bought in Toronto in 2015 on a lark as a non-runner, missing front cowling and exhaust - If you have a 1983 750ES front cowling let me know! Blue would be nice

    #2
    I'd check the #4 plug first to see how it looks. This should help determine if it's running rich.
    Jordan

    1977 Suzuki GS750 (My first bike)
    2000 Kawasaki ZRX1100
    1973 BMW R75/5

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