At the risk of breaking tradition of 1 cam in this forum....I love the 450 DOHC. Honda's most magic bikes, IMO, were the 450 DOHC, the 500/550-4 and the 400-4. My personal choice of riding the "big four" these last 36 years has more to do the with durability of that bike than with its personality.
The 450-2 will deliver more wallop per pound than almost anything out there, a real "kick-butt" twin. It's nimble, has excellent brakes (if they do wear quickly) and throttle response that is the envy of anyone who has ever ridden, but not owned, one. I usually beat every British twin except the 1967-68 Bonnevilles and the Norton 750s with mine. I had it for only 3 years before my father-in-law talked me out of it. His neighbor still owns and rides it today, 35+ years later!
Rules:
#1. Keep the carbs CLEAN. The vacuum pistons have very small clearances and the slightest amount of stickiness (from old gas, usually) will make the pistons misbehave and the mixtures will be erratic or just plain bad. Cleaning is easy: just loosen the clamps and twist the carbs sideways to get the covers off and the pistons out. Clean the bores and the pistons with acetone. Put 1 drop of very lightweight oil on your finger, apply it to the bores and the pistons, and reassemble. You'll be surprised at the difference! Remove the bowls and pilot screws, then spray carb cleaner through the passages. Clean the floats with acetone, check the float levels, and reassemble.
#2. The intake valve rockers wore badly. This was from folks running too light oil (cheap 10w40 or 10w30), and running it too long. The recommended change interval is 750 miles or less, because the top end really beats up the oil. Use 20w50 if you don't mind losing about 1 HP. Use Castrol or Torco, in any case, because it survives tehse hot-running engines better than almost anything but synthetics. Don't use synthetics, or you might lose your clutch. When starting it hot, WAIT 45 SECONDS BEFORE DRIVING, because it takes that long for the oil to reach the intake rockers on hot startup (honest!). If your lifters are worn, get new ones. They can be replaced through the adjustment cap holes. Set the intakes at .003" and the exhausts at .004" (I know the manual says .002" and .003", but that's for quiet, not for longevity). Worn lifters both clatter and reduce the lift a lot, as much as .100". Worst case, they also damage the cams. Look inside with a flashlight for score marks. They can be resurfaced or replaced fairly easily.
#3. A common malady with these was the points advancer weights getting corroded and stuck or the pivots wearing and getting loose. This makes it surge when trying to run along at steady in-town speeds (the carbs can cause this, too). Cleaning or re-bushing fixes them up.
#4. If you have more than 20,000 miles on it, try to get a new oil pump. This will improve many things, subtle things, that make it a happier ride.
#5. Hop-ups: after you've replaced those worn lifters and cleaned up the cam, give it a nice valve job to make it seal well, bore it .25mm (1st oversize) to gain almost 2 HP, mill the head .010" and remove the resulting sharp edge around the bore, trim the valve guide bosses on the intakes (they are too big), reassemble and set the timing an extra 2 degrees advanced. Grind off an extra spline on each torsion bar (for the valves) and reinstall 1 notch "extra" tight. This will let you spin 10,500 RPM safely, and it will, very willingly. Use the gearing from the CL model (it's slightly lower) if you have a CB. Get good tires: you're gonna need them after this. Replace the worn swingarm bushings and install tapered rollers in the steering head. Then, you'll wonder why you ever wanted to ride anything else.
The 450-2 riders' motto used to be: "After all, enough is enough!" It's hard to argue with that bike.
