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81 Jet Sizes
I bought my Special new and it came from the factory with 110 main jets on all four carbs. According to the shop manual the Standards had 120's for the center two cylinders and the outboards had 115's. I have a new set of Standard carbs in my stash and they also have this staggered jetting arrangement but they have rubber caps over the pilots and the 81 Special does not have these caps and so it appears the pilots in the 80-81 Standards are feeding off the mains like the 78-79 did hence the larger main jets. A stock 80-81 Special with a Kerker 4 into1 header which employ's Kerkers standard 1.5 inch glass wrapped baffle responds well with 112.5 mains,stock pilots and the idle screws tured out 3.5 turns from lightly seated.The 2 inch and 2.5 inch core will need 115's and in some cases the needles which are not adjustable with E-clips like the 78-79 will need to be raised with small .020 inch (1/2mm) thick washers. I used Kerker as an example but a similiar flowing pipe would get the same.The mains in a box stock 80-81 Special and Standard are close if your exhaust are stock but they are lean at idle and off idle and in the mid range as the factory leaned this part of the fuel curve down for cleaner emissions.The jet numbers I have mentioned are applicable for an altitude of sea level up to about 1500 feet. Generally,you decrease the main jet by 1# for each 2,000 feet of elevation increase.I live in St. Louis which has an elevation of about 450 feet but if I was in the mile high city of Denver my tune up would be dramatically different.The factory gave these things a tune up (jetting and so forth) that would enable them to be operated everywhere but because of the wide variance of altitudes in which they are used, they do not run perfect anywhere unless you tune them for your area.If you are not positive as to the application of the carbs you have,you can remove them and there will be a part number for the carbs acid etched somewhere on the main body of the carb.The numbers can sometimes be diffulcult to locate (I used a Magnifying glass to find mine) but the numbers are on there. Happy tuning.
I bought my Special new and it came from the factory with 110 main jets on all four carbs. According to the shop manual the Standards had 120's for the center two cylinders and the outboards had 115's. I have a new set of Standard carbs in my stash and they also have this staggered jetting arrangement but they have rubber caps over the pilots and the 81 Special does not have these caps and so it appears the pilots in the 80-81 Standards are feeding off the mains like the 78-79 did hence the larger main jets. A stock 80-81 Special with a Kerker 4 into1 header which employ's Kerkers standard 1.5 inch glass wrapped baffle responds well with 112.5 mains,stock pilots and the idle screws tured out 3.5 turns from lightly seated.The 2 inch and 2.5 inch core will need 115's and in some cases the needles which are not adjustable with E-clips like the 78-79 will need to be raised with small .020 inch (1/2mm) thick washers. I used Kerker as an example but a similiar flowing pipe would get the same.The mains in a box stock 80-81 Special and Standard are close if your exhaust are stock but they are lean at idle and off idle and in the mid range as the factory leaned this part of the fuel curve down for cleaner emissions.The jet numbers I have mentioned are applicable for an altitude of sea level up to about 1500 feet. Generally,you decrease the main jet by 1# for each 2,000 feet of elevation increase.I live in St. Louis which has an elevation of about 450 feet but if I was in the mile high city of Denver my tune up would be dramatically different.The factory gave these things a tune up (jetting and so forth) that would enable them to be operated everywhere but because of the wide variance of altitudes in which they are used, they do not run perfect anywhere unless you tune them for your area.If you are not positive as to the application of the carbs you have,you can remove them and there will be a part number for the carbs acid etched somewhere on the main body of the carb.The numbers can sometimes be diffulcult to locate (I used a Magnifying glass to find mine) but the numbers are on there. Happy tuning.
Sounds like someone may have put a carb kit in there, and found they had the rubber caps and the pilot towers were open and probably figured they went there, when they are only used for the 78-79 or 80's with that tunnel! The caps are otherwise thrown away for the 80-81-82 carbs that don't have that tunnel! 
T.C.
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