Why a CM?

The growing popularity of rebuilding or customizing vintage motorcycles, especially the cafe racer scene, has had a dramatic impact on the price and availability of classic CB series Honda motorcycles.  Honda CBs which were once plentiful junkers selling for below $500 are now hard-to-find "classics" sold at premium prices.  Even non-operational, poor condition, or incomplete classic CBs are sought-after commodities.  This has forced those on a budget who dream of building a custom bike to consider less popular, but more affordable alternatives.  More and more, that alternative is the Honda CM series motorcycle.

Why bother customizing a CM series?

• Low cost of entry.  A builder can still find a decent, running CM with a title for $500-800.
• High availability.  A builder can quickly and easily locate an affordable used CM and be more discriminating in the selection process. 
• Mechanically simple & reliable.  A CM is a great place for a novice motorcycle mechanic to start clocking wrench time. With greater the simplicity comes less frustration and greater success rates. 
• Factory electronic ignition.  Pre-1978 motorcycles typically utilize a point style ignition.  These are complex and not as reliable as electronic ignition.  Electronic ignitions can cost hundreds of dollars and are one of the first upgrades applied to classic Honda CBs.  Why go through the time, expense, and hassle when one can purchase a bike with factory electronic ignition?
• Some parts easily interchange with universal or CB parts for quick, easy upgrades.  For example, the front forks for a CB550 are a quick swap-out which will net the rider a better front brake and suspension.  Most inexpensive, bolt-on universal parts will work with a CM.
• Twins are far easier & cheaper to work on than 4 cylinder motorcycles.  Rebuilding and tuning 2 carburetors requires a fraction of the time it takes to perform the same job on 4.
• Used parts and parts bikes are easy to source.
• Personal satisfaction.  Sadly, some people would never have the experience of fixing up and customizing a classic motorcycle if forced to pay CB prices.

What are the drawbacks & considerations of customizing a CM400?

• The CM was designed to be a commuter or beginner motorcycle, while performance was more the goal for a CB.  A CB typically has better brakes, a stiffer frame, better suspension, better overall handling, and better weight to power ratios.
• The lines of a CM do not lend themselves to the cafe racer form as well as that of the CB.  Expect to do heavy frame, seat, and tank fabrication & modification to achieve the cafe racer look.  Although not impossible, CM is better suited as a bobber, brat, or roadster style custom over that of a cafe racer.
• Aftermarket performance parts for the CM are not as plentiful as they are for CB series Hondas.  The market never supported CMs simply did not have the same following or performance expectations as the CB series bikes did.
• OEM Honda parts are starting to become more scarce as the bikes age.
• This is a 30 year old motorcycle...  Any rubber on the bike should probably be replaced if it is not leaking already (fork seals, shifter seal, oil filter seal, carburetor parts, etc...).  Every day the engines gather more miles and are not cost effective to rebuild, even if you do the labor itself.  One can quickly invest a lot of time and money in simply restoring the motorcycle to good mechanical condition.
• A builder can quickly overvalue a CM.  It will be hard to sell a CM for more than $1200 no matter what you have invested into it.  Before committing to any purchases, make a list of all the known upgrades and repairs you intend to do.  Estimate a cost for each line item, then total it up.

Remember, in the end, this is all just a hobby.  Few people ever profit from their hobbies.  If you can do this and walk away with greater skills or a deep sense of personal satisfaction, then maybe restoring or customizing a CM400 isn't such a bad idea after all.