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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
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
)))))
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