That bike is a long way from original, with a 16" rear wheel, different exhaust, misrouted fuel lines...the fuel lines should go down from the petcock and then thru 2 holes in the right side of the carb mount bracket to prevent the bubble(s) that are currently trapped where those hoses turn downward toward the carbs. If those holes in the bracket are missing on the right side, then the carbs are from the K5/6 or F0 bike, where the petcock was on the left side and those holes were flipped.
A special note, though: in the K4 (late) production the carb bracket can have 4 holes in it for the hoses, 2 on each side in the same hi/lo arrangement, or the low hole only (2 different brackets during 3/74 thru 10/74 production were seen on K4). The LH fuel petcock first appeared in late K4, in the famous "50 MPG" ads in the magazines during the US gasoline shortage of that era: these bikes also received the same ignition coils that were later spec'd for the K5-onward bikes (4.3 ohm primary instead of 4.6 ohms). On the showroom you could see both LH and RH petcocks on 750 bikes that were designated K4 (this was during the later summer months, like July/August). We later learned that the LH versions had the 'lean burn' engine with the 1mm taller cylinders: those bikes also had the little plastic caps on the idle air screws (like are found in the F0 with the "086" series carbs) and the floats were set to a more-than-26mm height in many cases. The idle air screws have extended heads that stick up out of the carb bodies (to both fit the plastic caps and ID the carbs quickly) and are longer than the earlier versions.
While those bikes could actually achieve 50 MPG at 55 MPH on flat hiways with no headwind, windshield, fairing nor saddlebags, they also could not reach 100 MPH. (This can be fixed, but takes some work...that's noted in my book.
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...not that there's anything wrong with teasing 50 MPG out of them again these days?
