Some of you guys have SOHC cb750s (1969-1978) and are new to the bike so when I someone else posted these quick and simple mods to make the bike a better handleing bike I figured I should post it over here too. Most of these mods I have done to my bike over the years and they really work well.
The only thing I disagree with the author about is the ribbed front tire,I run a metzler with a symetrical tread of the same type as my rear and I don't get any headshake on deceleration. If you do, go with a steering dampner as suggested in #4, rather than go back to a ribbed tire, ribbed tires are not performance tires and also the cb750 tends to get close to headshake at the ton anyway so the dampner is just sound thinking. The other thing I didn't mess with is the shocks, I'm 6'4" and don't need to drop the bike and also the bike came with very nice koni dial a rides when I bought it. I am also not a big fan on the air forks conversion simply because it is overused improperly and newbies sometimes blow out their fork seals. That being said I do have a spare front end with the conversion ready for whenever I move somewhere with better roads. Some of these tricks are universial to other bikes and I encourage others to post about these kind of mods on other bikes. That being said here is the post:
I've often been asked, by those who've ridden mine, why my 750 "feels" like a much smaller bike. Yours can be made to "feel" like the hotrod CB450 with 750 power by doing these things.
#1. Replace the steering head bearings (little balls and tracks) with VERY HIGH QUALITY tapered roller bearings. DO NOT use the Japanese or other oriental ones: use Timken. There IS a significant performance difference. And, set them up slightly tight, as they will wear in after about 500 miles.
#2. Replace the rear swingarm bushings with tight-fitting, oil-impregnated bronze bushings. Change the oriental-style grease zerk fitting(s) with US-style zerks so the grease can actually be forced into the bushings. Lube those bushings generously when assembling them, and use new felt seals when you do.
#3. Get Timken or Reynolds wheel bearings for the front wheel (2 each) and the rear (3 bearings back there). They cost nearly 3 times as much as the oriental ones, and they are worth every cent.
#4. All of the CB750K-K5 models I have seen have the "optional" steering head damper mounts. Get one from Fox or a BMW shop and install it. Set the damping to medium for startup, then adjust to suit when you get used to it.
#5. Tires. Use ONLY ribbed tire pattern in the front of a CB750K2- or later model. You can get away with a blocked pattern on a K or K1 model, because they don't "shake their heads" during deceleration. A ribbed front tire pattern helps make the bike run more stably under most street conditions, and it does not "wash out" suddenly in corners. The rear must be a symmetric pattern, preferably a block pattern. The new "sideslash" patterns on today's crotch rockets will cause sideways drift under heavy acceleration on wet (or slick) surfaces with the 750 geometry. Sizes: K5 and earlier: front must be 3.25 or 3.50 by 19". Rear is usually 4.00x18, some later ones had 17" rears and should be 4.50x17. IF YOU USE TT tires, use the 4.10x19 front and 4.50x18 (or 5.10x17) rear, AND ON BOTH ENDS. DON'T use a TT on one end only, and DON'T use them for heavy touring loads, they'll be all over the lane. These tire size combinations preserve the already-short 3.25" trail on the front end of these bikes, as well as the load rating. Larger rear tires will cause wobble, every time, because they shorten the trail.
#6. For those of you who have short inseams: your first choice should be to install 12" length rear shocks. Get 110-lb straight-wound or 90/120-lb progressive springs. If you install "lowering blocks", you will get a VERY stiff rear suspension, because the increased cant of the rear shocks will not allow them to compress over bumps. Shy away from those blocks. After installing these shocks, lower the front triple clamps about 1/2" on the front forks.
#7. Use teflon-mixed oil in the front forks. Get teflon-coated seals that are slighty shorter in length (1/4" instead of the stock 5/16" to 3/8" stock units). These will "float" up and down slightly between the top of the fork retainer and the upper C-clip, which makes them seal better and respond to minor road irregularities MUCH better. Install the optional steel washer ABOVE the seal (good kits include these washers). Drill and tap the fork caps and install threaded Shraeder-type air valves (found at tires stores, used on mags), one in each fork. Run about 10 PSI pressure if riding single, 15-20 if carrying heavy loads.
If you do ALL of these things, you will not believe the difference the next time you hit a corner. It will feel like the bike lost 100 lbs somewhere...