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  • KC16A Carb

    Tillotson KC16A Carbs: The 'Yogi' analysis. Yogi said you can see a lot just by looking. So, lets look carefully...

    These ‘racing only’ model Tillotson carbs were only supplied on the Mercury 25SS , 22 cu. in. race motors. They were not supplied on any regular service motors.

    If we look in the carb literature, to see what they were based on, of course, they were not a 'clean sheet' design, the other service motors where the 1 1/16" venturi version of the KC series carbs were commonly used are mostly on Merc 650 fours with a displacement of 66 cu. in. with two carbs...

    Other common KC models were 1 3/16" venturi, with a different shape/profile.

    The KC16A was a 1 1/16" diameter KC that shares many characteristics with a KC15A Merc 650 carb. It appears the KC16A was the factory racing version of the KC15A. Some KC16A's were actually factory restamped over the KC15A numbering.

    Differences were the KC16A was supplied with an awful plastic inlet needle, a full butterfly and a different idle tube. Other differences were external, like throttle linkage parts, etc. Main jet was .061" fixed jet, same as KC15A.

    Now the bad news: These carbs, IMHO, are a great design, poorly executed. Quality control was awful. The late, great Vern Kargus told me in the 1970's that these carbs were made just barely good enough to run, based on his experience in 25SS hydro. I bought ten brand new KC16A's from Mercury, no two were quite alike. There were imperfections in machining, lengths of tubes, orifice sizes, etc. It was a real struggle to make these into matching pairs for 44 Mod.

    I fiddled with these KC's for two seasons, testing, finding what works, what doesn't work, before I switched over to racing them in place of my well developed KA's. They are a very good carb when right, but the trick is to get them right.

    BTW, they also start hard, as they simply don't carburate at roping speed feeding just 22 cu. in. displacement when they were designed for 50% more, 33 cu. in. per carb. Start them on 'prime' squirted way back into the reed cages, then with that starting rpm velocity through the venturi, they start to run as they should. If they don't start, they almost always need more fuel.

    Hope this helps.

    Jerry Wienandt

    Trident Racing




  • #2
    Originally posted by trident View Post
    Tillotson KC16A Carbs: The 'Yogi' analysis. Yogi said you can see a lot just by looking. So, lets look carefully...

    These ‘racing only’ model Tillotson carbs were only supplied on the Mercury 25SS , 22 cu. in. race motors. They were not supplied on any regular service motors.

    If we look in the carb literature, to see what they were based on, of course, they were not a 'clean sheet' design, the other service motors where the 1 1/16" venturi version of the KC series carbs were commonly used are mostly on Merc 650 fours with a displacement of 66 cu. in. with two carbs...

    Other common KC models were 1 3/16" venturi, with a different shape/profile.

    The KC16A was a 1 1/16" diameter KC that shares many characteristics with a KC15A Merc 650 carb. It appears the KC16A was the factory racing version of the KC15A. Some KC16A's were actually factory restamped over the KC15A numbering.

    Differences were the KC16A was supplied with an awful plastic inlet needle, a full butterfly and a different idle tube. Other differences were external, like throttle linkage parts, etc. Main jet was .061" fixed jet, same as KC15A.

    Now the bad news: These carbs, IMHO, are a great design, poorly executed. Quality control was awful. The late, great Vern Kargus told me in the 1970's that these carbs were made just barely good enough to run, based on his experience in 25SS hydro. I bought ten brand new KC16A's from Mercury, no two were quite alike. There were imperfections in machining, lengths of tubes, orifice sizes, etc. It was a real struggle to make these into matching pairs for 44 Mod.

    I fiddled with these KC's for two seasons, testing, finding what works, what doesn't work, before I switched over to racing them in place of my well developed KA's. They are a very good carb when right, but the trick is to get them right.

    BTW, they also start hard, as they simply don't carburate at roping speed feeding just 22 cu. in. displacement when they were designed for 50% more, 33 cu. in. per carb. Start them on 'prime' squirted way back into the reed cages, then with that starting rpm velocity through the venturi, they start to run as they should. If they don't start, they almost always need more fuel.

    Hope this helps.

    Jerry Wienandt

    Trident Racing
    Jerry

    What specifics of "finding what works, what doesn't work" did you determine for these KC16A carbs ?

    Thanks
    Pete
    "Keep Move'n" life is catching up!
    No man's life, liberty or property are safe while the legislature is in session.

    Comment


    • #3
      Start here, per above:

      Now the bad news: These carbs, IMHO, are a great design, poorly executed. Quality control was awful. The late, great Vern Kargus told me in the 1970's that these carbs were made just barely good enough to run, based on his experience in 25SS hydro. I bought ten brand new KC16A's from Mercury, no two were quite alike. There were imperfections in machining, lengths of tubes, orifice sizes, etc. It was a real struggle to make these into matching pairs for 44 Mod.

      After eliminating bad parts from the manufacturer, like a main nozzle drilled with a nasty swirl up the ID, then pay very close attention to alignment of things like the idle tube in the main nozzle. Some tubes need to be bent like a pretzel to align as the castings were so poorly machined. What to use as a replacement for that awful plastic inlet needle. Float height. And so on...

      BTW, I liked Grose Jet, and Parker inlet needle replacements, both unobtanium today. Recommend 1395-9258--1. Two dashes.

      Its all just attention to detail. And frankly, some are so bad, they'll never be perfect!

      Good luck.



      Comment


      • #4
        Originally posted by trident View Post
        Start here, per above:

        Now the bad news: These carbs, IMHO, are a great design, poorly executed. Quality control was awful. The late, great Vern Kargus told me in the 1970's that these carbs were made just barely good enough to run, based on his experience in 25SS hydro. I bought ten brand new KC16A's from Mercury, no two were quite alike. There were imperfections in machining, lengths of tubes, orifice sizes, etc. It was a real struggle to make these into matching pairs for 44 Mod.

        After eliminating bad parts from the manufacturer, like a main nozzle drilled with a nasty swirl up the ID, then pay very close attention to alignment of things like the idle tube in the main nozzle. Some tubes need to be bent like a pretzel to align as the castings were so poorly machined. What to use as a replacement for that awful plastic inlet needle. Float height. And so on...

        BTW, I liked Grose Jet, and Parker inlet needle replacements, both unobtanium today. Recommend 1395-9258--1. Two dashes.

        Its all just attention to detail. And frankly, some are so bad, they'll never be perfect!

        Good luck.
        I still have some old Gross Jets kicking around.....)))))



        Comment


        • #5
          Note there are four different ID sizes, for the KC on gas, I recommend the smallest one, Grose Jet T-Son 902 .084"



          Comment


          • bill van steenwyk
            bill van steenwyk commented
            Editing a comment
            I also have some grose jets left. Will check sizes on the package and post back here.

        • #6
          Jerry,,,

          If the 16A was so bad and not that much different, then why not just use the 15A with a few mods????

          15A's are all over the place, just thinking out loud...



          Comment


          • #7
            Because the KC15A is made just as badly as the KC16A and requires even more modification? Same issues on all those KC's of that era.

            That would be the easy answer, but due to the small supply of KC16's available, it becomes a good answer. Fix all the problems, same as the 16, then make some new parts and you have KC16A 'clones'. And you have a much larger supply of those to work from...

            I ran both. Put right, they both run well, but OEM either can be really bad!



            Comment

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