Wednesday, February 17, 2021

Honda 250-305s… pros and cons

 As the alleged “Guru” of the 1960s 250-305cc twins, I have learned a lot about these bikes, most of which has been written into my “Restoration Reference Guides” for each of the three models. In monitoring various forums and vintage Honda groups, I continue to see people digging these bikes out of garages and falling down buildings, just in time to start a rescue project. Usually, the new owners have little in the way of knowledge or reference beyond Honda’s little efforts to create shop manuals. Scrambler owners are surprised to find out that there was no “305” updated version of the “250” shop manual! The CL72 shop manual is a decent place to start but there are no references to the “big-brakes” and alloy forks, so you have to just figure it out by yourself or ask for knowledgeable assistance.

I have owned all of the US-market 250-305s, including a couple of CE71 dry-sump models. I used my first-hand experience with the various bikes owned in the past to compile the reference guides and share what I know with forums and other groups. These bikes have stood the test of time with classic styling, reliability (when properly maintained) and amazing performance and longevity. There were shortcomings in a few areas, which are well-known to most veteran owners, but the appreciation of these well-made motorcycles continues to grow. So, here’s my take on the three pillars of vintage Honda twins.


With engines that were lowest in horsepower, Dream engines can last for many years, however, there are features that are shared with all of the 250-305s, which cause problems with higher miles accumulated on these unique machines. Honda’s choice to bury the spark advancer system deep inside the cylinder head in the middle of the camshaft sprocket is a puzzler. Ironically, the CE71 Dream Sports did have a separate spark advancer on the outer end of the camshaft, but when Honda changed from dry-sump to wet-sump engines, they put the spark advancer in the middle of the camshaft.

Problems arise here when the engines have aged and have been ridden higher mileages. The return springs on the advancer weights tend to stretch and loosen, which prevents the weights from coming back to a normal stopped position. The weights also have little bonded stoppers on the ends to cushion the return to rest. These rubbers harden and eventually break off, causing the weights to return further than originally designed. This adds more travel to the advancer weights, which causes an excessive spark advance to come into play. In order to prevent the spark advance from going beyond 45 degrees, you have to retard the idle spark timing back towards TDC, which engines don’t really like. Idle spark timing is best in the 5-10 degrees before top dead center, so setting idle timing at TDC can create rough idle, plus the weights tend to swing out prematurely causing the idle speed to raise unnecessarily.

Spark timing has a big effect on manifold vacuum signals which are acting on the carburetor’s idle circuits. Advanced spark timing increases vacuum signals, which pull more fuel into the engine, which then makes it run faster, so the whole effect snowballs out of control. On a single-carb Dream, the vacuum signals are amplified as two cylinders are pulling vacuum signals alternately.

What else had become apparent over the years, is that the point cams, which open the points at just the right time are not symmetrical on both lobes, often varying 5 degrees between engine cycles. You can watch the spark signals waver back and forth using a dynamic timing light. Another factor that shows up with varying timing signals is that the camsprockets are basically riveted together and after years of enduring camshaft lobes pushing and pulling the camshaft over center each engine cycle, the rivets loosen up, allowing the center camchain sprocket to begin to shift back and forth on each engine rotation. This affects both valve timing and ignition timing, as the parts shudder against each other during engine operation.

The camsprockets can be TIG-welded at the corners to anchor the sprocket to the rest of the assembly, but when the weight pivots wear out and/or the rubber cushions fail, you really can’t remedy the situation, short of replacing it with a new or good used replacement. Adding to the complexity of the situation, Honda changed the camshafts and sprocket spline dimensions through the years, so you must match a replacement sprocket to your camshaft splines. And finally, the camsprockets for Dreams and CB/Cls are different in that the Dreams have a faster spark advance curve using larger, heavier weights that swing out quicker as engine speeds increase. Are you following me so far?

Another note about the engines; they have some wear parts in the bottom end, too. The bronze low gear bushing has a raised center rib to keep two gears apart, but the thrust from the low gear will eventually wear the rib out so it slides off as a separate ring. The kickstarter pawl is in constant contact with the inside of the low gear and eventually wears out causing slippage when kickstarting the engine. The other wear item are the primary chains, which originally were offered in three different strengths, but superseded to the 268 code ones for the Super Hawks. All these endless chains are the same size and length and with over 250,000 engines built, the supplies have dwindled down to next to nothing.

CA72-77 Dreams

Considering Dreams were basically designed in the late 1950s, the basic chassis didn’t change a lot for 10 years. Many of the wet-sump Dream parts share their roots with the 1957-60 dry-sump models. On the plus-side, they were designed to be “Touring” bikes, ones that keep the rider as clean as possible during the ride. Large fenders and enclosed chain guards help prevent unnecessary road grime and chain lube from reaching the rider and passenger. Domestic versions had solo seats and luggage racks which could either be used for hauling materials or with the installation of a clip-on passenger seat, you have a dual rider machine.

All Dreams have the Type 2 (360 firing) crankshaft, which helps give the little single-carb engine a boost in torque, coupled with a lower geared transmission to help move things along The 360 crankshaft firing engine can cause some frequency vibrations that typically cause fractures back in the rear fender/tail light region, due to the sheet-metal construction of the frame. Dreams have shorter cam timing for low-end torque, but run out of breath past 8k rpms due to the single carburetor and cam timing limitations. Dream engines have lower compression ratios than the CB/CL counterparts.

Apart from a lack of horsepower (rated around 24 ponies), the riding experience is hampered by (1. a lack of suspension damping/control at both ends and (2. terrible, tiny, single-leading shoe brakes on both wheels. Other rider complaints center around the “late Dream” (CA78) slide throttle for the carburetor, which has no real return to idle function if you let go of the throttle. Early Dreams used a twist throttle, like the CB/Cls, which allows more control of the throttle function.

Mechanically, for the most part, the Dream engines are pretty much the same. The early model machines used a tall, thin and long 12v battery that was only used on that series of machines and is long out of production. From 1966-onward, Honda retooled the bike to take the 12N9-3A battery used in Super Hawks and lawn tractors. These are much more commonly available, except there are some versions that have vertical posts, vs the flat horizontal posts that the bikes were designed for originally.

CB72-77 Super Hawks

These hotrod “cafe racer” models, which offered flat handlebars a decade before “cafe racer” was a thing, are the star performers of the trio. Early models, with the 9.5 compression engines could hit right around 100 mph with nice big 200mm (8 inch) dual leading shoe brakes to bring them to a rapid halt. Early 1961 models had SLS front brakes (still 8”) and DLS rears for some reason. Honda saw the light early on and switched back to DLS fronts, which were probably some of the most powerful production brakes during that era. The drawback on DLS brakes is that they are very powerful GOING FORWARD. They lose all of their mechanical advantage when the bike is going backwards, however. It’s a somewhat disconcerting feeling to try to hold a Super Hawk on an inclined stop sign/light, when it wants to slowly creep backwards on you, no matter how hard you pull the brake lever in. Most of the time that isn’t a problem, but be aware of the shortcomings of the brake system designs if you come up against this situation; nose pointed uphill at a stop.

With flat bars, the riding posture is leaning forward into the wind, balanced by the air pressure pushing back against your chest. The “flat bar” CB72-77s have “the look” that is a classic pose and mostly preferred over the later 1966-67 low rise bars offered in the US. In actual practice, the low rise handlebars offer more rider comfort for around town riding and for those of us in our advancing years.

My pet peeve for CBs are the stupid friction pivoting driver footpegs and the non-folding passenger pegs. Invariably, as you are shifting the bike around while getting it pointed down the driveway is that the drive pegs brush up against your shins and promptly fold UP and stay UP until you manually push them downwards again. It’s very annoying to be riding around and having to be concerned with the footpeg positions, which are easily displaced from normal.

The rear pegs are solid bars with rubber peg rubbers and if you are standing next to the bike and pushing it around, you will invariably contact the rear pegs with your shins. In the past, I have opted to find the domestic non-folding driver pegs used outside of the US and on CP77s and leaving the rear pegs off, as there is seldom a reason to have a passenger on the back of these bikes

More irritants center around the goofy forward-kicking kickstarter arm. It is either contacting your instep when you are riding and particularly when you are trying to use the rear brake pedal and/or the extended end of the kickstarter arm catches your pants leg and starts to pull you off balance as you struggle to untangle your pants from the kickstarter arm before you tip over in the street. I hate that!

Because of the nature of the spine frame arrangement, dropping the engine out for service is relatively simple, apart from the fact that the engine weighs about 115 lbs. The frame design allows for light weight and responsive handling. The overall vibration levels are much less than the enclosed frame of the CL72-77 Scramblers, under similar circumstances. The Type 1 engine configuration (180 degree crankshaft) gives off a high-frequency, low amplitude vibration that is kinder to the chassis parts, although chain guards and tail lights have been known to have vibration cracks from the engines rocking couple firing. You can watch the rear fenders wiggle back and forth when the engines are idling and the bike is on the center stand.

Super Hawks had distinctively different front fork designs with the early versions made up of steel tubing and ends welded onto the tubes to create the axle holders and the threaded-on fork seal holders. The steel fork tubes can be easily damaged by inadvertent installation of excessively long fender and brake arm bolts that screw into the welded and threaded mounting pads. When the bolts bottom out in the tubing, it distorts the bore shape and the fork bushings jam up inside. The Type 2 forks were cast aluminum parts, with 2 bolt clamps at the bottom to hold the axle and offset bosses to mount the fender bracket. You can tell the difference on a stock bike right away, as the Type 1 steel forks are painted the same color as the frame, while the Type 2 alloy fork sliders are silver on all models.

CL72-77 Scramblers

From 1962-67, something like 80,000 Scramblers made their way to market, mostly in the US. When Dave Ekins and Bill Robertson took brand new CL72s down to the tip of Baja in early 1962, the stunt did wonders for Honda’s sales of their new “dual sport” Honda Scrambler model. Sales skyrocketed in the following years, then really exploded when Honda dropped a 305cc engine in the same chassis. CL77 production ran into about 68,000 units. With the sales successes of the 250 Scrambler, suddenly Honda thought, “Why don’t we make Scrambler versions of all our models?” and so they did. Honda did a bolt-on kit for the CB450 Bombers to make them into “450 Scramblers” back in 1966, before designing a companion model to the CB450 street bikes. There were Scrambler versions of 90s, 160s, 175s, 350 and aforementioned 450s. When the new OHC horizontal 50-70cc engines were produced Honda made CL70 Scramblers. Everyone LOVED the Honda Scramblers for their style and their perceived abilities to go off-road (just a little bit). Certainly, a lot of street bikes were stripped down and raced or ridden off-road, back then, but the stock suspensions were woefully inadequate for serious competition. And it was the same for the 250-305 Scramblers, which had the look, ground clearance and makings of an occasional off-road machine, but really needed some aftermarket help. Japanese shock technology was sorely lacking in the 1960s, with shocks limited to a couple of inches of travel and very little damping capability. That opened up new industries that specialized in improved shocks and fork kits to increase travel and dampening abilities.

The key feature that makes the Scramblers so much different than the Super Hawks is the level of vibration transmitted into the chassis from the engine and exhaust system mounting. Scrambler engines didn’t have electric starters for weight reasons, but that allowed for the frames to have a single down-tube in front of the engine to help strengthen the frame in off-road situations. The closed tube frame design lead to increased vibration transmission throughout the whole chassis, coupled with the long resonant exhaust pipes, which were bolted directly to the frame, caused increases in vibration levels throughout the whole bike.

Scrambler engines are basically Super Hawk engines without the tach drive and electric starter, so all the preceding comments about the engines apply equally here.

Scramblers were always geared shorter for better off-road riding and that lead to more rpms on the highway for long trips. The increased vibration began to cause failures of chain guards and fenders. Because the engine is bolted directly to the frame, all Honda engineers could do was to begin to isolate the rider from the vibration sources. Rubber-mounting of components lead to new footpegs, seat mounts, exhaust system mounts, rear fender mounts, battery mounting systems and even front fork ear cushions to reduce the headlight bulb failure rates. The CL77 rear wheel sprockets lost a few more teeth (37 vs 40 on the 250), as well, because many riders loved the look of the Scramblers, but didn’t always care to go off-road and highway riding got tiring after extended exposures to the vibration levels coming from the engines and being transmitted throughout the whole machine.

With high demand for parts and dwindling supplies, it can easily cost upwards of $10k to do a full restoration of these iconic machines. Most owners opt for the straight pipes with or without baffles or the “Snuff-or-Not” movable exhaust washer accessories. The long pipes have a distinctive resonance that gives them their unique sound.

Bill “MrHonda” Silver