CB750 K - F3
Engine Modifications
So, you're ready to build a chopper and are searching for an engine. Wouldn't it be nice to know what the pros and cons are of that particular engine?! Wouldn't it be nice to know what the Honda factory did to improve, before AND after, your engine number!? Read on brother...the Truth is Out There!
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Engine #    
CB750E-1000001   K0
CB750E-1000140   Bolt at the final drive changed from M8x80 to M10x82
CB750E-1000220   new lower case, engine case only available as set
CB750E-1000425   Transmission changed for better shifting
CB750E-1001081   new crankshaft
CB750E-1001760   7 instead of 8 clutch disks
CB750E-1003528   new final drive shaft and sprocket
CB750E-1005307   fixed right bearing of main tranny shaft
CB750E-1007220   new lower case, deeper oil pan
CB750E-1007414   End of sandcast engines
CB750E-1007415   introduced circular opening in lower case
CB750E-1009554   finned oil filter casing
CB750E-1010336   cam holders with additional oil passages, new rocker shafts and valve cover
CB750E-1014996   new exhaust valve guides, new valve guide seals
CB750E-1026144   new cylinder head, cylinder block: new central M6 bolt, cyl. block w/8 rubbers i/o 12. Case with guard to prevent damages from broken drive chains. New sprocket cover, new shift mechanism w/11 parts i/o 7
CB750E-1042806   weaker clutch springs
CB750E-1044813   K1
CB750E-1044805   new case, final drive 18/48 i/o 16/45 or 17/45, chain oiler
CB750E-1044812   carbs w/links i/o individual cables
CB750E-1044968   improved neutral position
CB750E-1056080   new clutch basket
CB750E-1064903   introduced spacial washerless bolts
CB750E-1068376   cramp for scavenge hoses
CB750E-1071336   fuel hoses 5.5mm dia. i/o 5.0mm
CB750E-1113723   grooves in gear shift rum changed from 0.5mm to 1mm for 4th and 5th gear
CB750E-1114461   new head gasket
CB750E-2000001   K2
CB750E-2061311   shorter oil hose w/white mark. Main jets 110, smaller cutouts in air filter case
CB750E-2200001   K3
CB750E-2200001   new cylinder head, new valve guide seals, improved oil passages to camshaft, new piston rings (three part oil scavenge rings), new cam chain guide, larger piston pin circlips, new final drive shaft, new sprocket cover
CB750E-2228679   new cylinder head, new valve guides, new valve guide seals, no more rubbers between fins
CB750E-2300001   K4
CB750E-2304501   new cylinder block, smaller cam chain tunnel
CB750E-2352923   new cylinder block
CB750E-2348093   crankcase mission cover now has gear indicator
CB750E-2372115   K5
CB750E-2428762   K6
CB750E-2470427   clutch almost indentical to F1: new clutch basket, new clutch cover and chrome cover
CB750E-2434657 to CB750E-2439607   new gear shift drum, new center shift fork for improved shifting. New gears on countershaft w/bronce bushings, new case
CB750E-2700001   K7
    carbs w/accelerator pump, shorter intake rubbers, new final drive shaft, sprocket w/center bolt, wider chain line (as F2), final drive 15/41, new clutch, new camshaft (as F1), new pistons (as F), compression ratio 9.2/1. New transmission: 4th gear 1.133 i/o 1.087. Final drive gear 50 teeth i/o 56 (as F1), primary drive 1.985 i/o 1.708
CB750E-2719530   new valve guides
CB750E-2719997   new cam carriers (as F2)
CB750E-3000001   K8
    new intake and exhaust valves, new valve spring retainers and cotters
CB750E-3021913   new cylinder block w/larger cam chain tunnel
CB750FE-2500004   F1
    new camshaft, carbs w/additional idle air. New pistons, compression ratio 9.2/1. New case w/o primary chain oiler. Final drive gear ratio 43/50 i/o 48/50. 4th gear on main shaft 31 i/o 30, 5th gear on countershaft 31 i/o 32
CB750E-2600014 and CB750GE-1000014   F2
    new cylinder head with bigger valves (34/31mm i/o 32/28mm), larger combustion chamber, larger carb mount rubbers, stronger cam chain, new camshaft, harder valve springs, new retainers, cotters, new pistons compression ratio 9/1. New rod big end bolts and bearings, harder clutch springs, additional fins on crankcase, larger fins on oil pan, "oil cooler" - finned plate between oil filter case and engine. Final drive 15/43 or 14/43.
CB750E-3100001   F3
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Source: The Satanic Mechanic  http://ourworld.compuserve.com/homepages/axelg/engine.htm (now defunct)