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Honda CB250RS Repairs and Resuscitation Progress

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I had the seller’s help in loading the bike into the 1995 Ford F150, but I was worried about the unloading part of the adventure because the bike had NO FRONT BRAKES due to hydraulic failure of the master cylinder. Fortunately, a visiting ATT technician “volunteered” to help me guide it back off the truck without harm to the bike or myself. Once it was on the centerstand, the focus was to get the brakes fixed first. The hefty master cylinder unbolted with a couple of clamp bolts and loosening the banjo fitting on the back of the unit. It had been drooling brake fluid out past the piston seals and dust boot for quite awhile, so all of the brake fluid deposits were mostly hardened and gooey in spots. Some brake cleaner spray in strategic locations, plus my HONDA snap ring pliers combined to remove the piston snap ring to empty out the master cylinder of all the old gummy parts. There was a spare 377 code master cylinder kit in the spares box and it appeared that much of it would fit in this model specific master cylinder. The piston was reused, but the new pressure cups were a perfect match and installed once the bore and body were cleaned thoroughly.

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Once the master cylinder was primed again, the unit was reinstalled on the handlebars so that the newly resealed part could do the next task, which was to push the front brake caliper piston out of the caliper bore. Fortunately, this went pretty well, but the caliper seal ring and the piston had some superficial damage due to moisture corrosion from sitting for such a long time. Eventually, the piston was extracted and cleaned. The seal ring was carefully cleaned and inspected for any serious damage. Once the caliper bore and seal ring grooves were cleaned, the old parts were reinstalled. The caliper was remounted on the front fork mount and it bled air out quickly. So, after about an hour’s worth of work, the brake finally had a solid front brake system again.

From there, the seat/tail piece was removed, then the fuel tank taken off and placed aside while the carburetor was loosened up for removal. Once the cables and clamps were all dealt with, the carburetor body came free and was disassembled for inspection and cleaning. The inside of the float bowl was remarkably clean, with just a bit of varnish down in the deepest recesses of the bowl. The pressed-in pilot jet was dislodged, cleaned and reinstalled. The 32mm carburetor has an accelerator pump system installed, with a very long pump diaphragm rod used to contact the carburetor linkage. There were some signs of rust/corrosion from old trapped gas/moisture atop the diaphragm retainer, but it seemed to clean up and should be fully useable once again.

The foam air filter sleeve disintegrated as soon as I touched it, so the whole filter assembly was directed to the trash can, where the remaining filter foam was peeled off and discarded. The filter part number has a -471-code (CB250RS), however checking the part number revealed that the CM250 street bike uses the same part, here in the US. A LOT of the parts on this bike are model specific and a search of eBay auctions all led to UK or Australian sites for any loose parts offered for sale.

The last set of tires installed were a size or two too large, so some smaller rubber is in order to make the bike handle like it did originally. Standard tire sizes are equivalent to 3.00x18 front and 3.50x18 rear, which mount on factory alloy rims.

Although the bike is loosely based upon the XL250 Enduro model, the engine has a larger carburetor, more aggressive camshaft timing and a 9.2:1 compression piston installed. The 5-speed transmission gearing is also more street-biased. The fairing is a Hondaline accessory part, as is the rear luggage rack. Both mufflers have some little skid marks on the outer rear edges, but whatever crashes may have occurred in its life must have been fairly minor.

Numerous receipts came with the bike, showing lots of oil changes, tire changes, chain and sprocket replacements and other minor work. A concern for me was to take a look at the balancer chain tensioner adjustment, which must be done manually. The balancer adjuster is beneath the clutch cover, so that requires draining the oil and removal of the cover and de-compression cables. The adjustment for the balancers is a slotted plate, which is spring loaded. Releasing the locking nut allows the spring to pull the plate across the slotted section until it comes to a stop. After the first couple of adjustments, the balancer chains continue to stretch to the point where the adjustment slot runs out of room. The balancer weight and snap rings must be removed and the adjuster plate relocated on large shaft spines one notch. This puts the adjuster back into a range where future adjustments will continue to be allowed with just a loosening of the locking nut. Fortunately, because the engine is based upon the XL250 design, the engine side cover gaskets and cover seals are still available from Honda dealers.

When I owned the bike, I think other oncoming riders thought it was a Kawasaki 550GPZ, at first glance, due to the dual exhaust pipes feeding into dual mufflers, plus the overall sleek 80’s styling was consistent with other manufacturer’s offerings at the time. The squared off headlights were used extensively in the 1980s by most manufacturers. The headlight bulb is replaceable in this model, but the bulbs may be difficult to source these days. A search for the headlight bulb turned up two new ones in Australia which were $30 each, but shipping was $40! The replacement battery is a YB9-B model, which is fairly common in the US. The petcock is the same as the CM400C models, but cost about $75 each. The petcock lever plate is riveted onto the body, so the inside 4 hole gaskets cannot be replaced without some fancy drilling, tapping and installing new, tiny 3mm metric screws.

With some fresh parts in hand, work continued on completion of the carburetor cleaning and reinstallation. There was about a gallon of fuel in the tank, which was drained out to check the petcock screen condition. Amazingly, the fuel was clear and the tank was clean inside after all those years of storage. Although a new petcock was ordered, the old one was reinstalled as was the old gasoline! The rear wheel was off the bike receiving a replacement 3.50x18 Dunlop K-70 rear tire, taken from a recent CB77 acquisition (way too big for a Super Hawk anyway). The wheel was taken to the local Honda dealer, Southbay Motorsports, which has a tire machine that can remove the old, hardened tire and install a new one without scratching up the 1.85x18 DID alloy rim.

So, with a new battery installed and just one wheel on the bike, the fuel tank was mounted up with a new piece of fuel line and the reconditioned 32mm carburetor fed some 10 year old gasoline for the first time in 10 years! The carburetors have an accelerator pump, which gives a nice squirt of fuel to the intake system. With full choke and a couple of firm kicks, the motor fired right up, sounding none the worse for wear after 42k miles and 10 years of storage! Initially it ran for about 45 seconds, then quit suddenly, which can be a scary event in the event of some kind of catastrophic engine failure, but it turned out that the petcock was in the ON position and there wasn’t enough fuel to feed it until RESERVE was selected. Warming the engine up for 3-4 minutes, the only signs of some aging was a little blue smoke out the mufflers, when the throttle was twisted vigorously. The smoke continued to diminish as the warm-up continued. The old spark plug was a D9EA, which is one range cold for normal use, but fine for continued highway touring. Eventually, the plug fouled over and was replaced with a DR8EA. The old plug came out dry, without signs of excessive oil consumption. So far, so good!

With the rear wheel retrieved and reinstalled, the bike was nearly ready for its first test drive in at least 13 years (last registration tags on the license plate are 2001). It only lasted about 100 feet… I had forgotten to put the petcock back onto RESERVE again! Once it re-fired again, the first stop was the local gas station for a few gallons of fresh premium fuel to mix down the very old gasoline remaining in the fuel tank. With 2.5 gallons of gas, the bike was headed out on its first maiden voyage with the original owner back onboard again. The engine pulls well from moderate engine speeds and the transmission gears are evenly spaced, but shifting is a little bit notchy. With healthy front brakes, strong rear brakes and an engine that purrs, the reunion was a success, rekindling fond memories of my long-lost imported CB250RS Honda and the ride up the California coast over 30 years ago.

A new front tire and tube are on order and will be scheduled for replacement at the earliest possible moment. The new air filter sleeve is installed and a NOS tachometer is coming in from the UK, a recent find on eBay auctions. A trip to DMV will be in the offing, along with signed release of the CB250R license plate, so all the registration, personalized plate and title paperwork will finally be current and in my name. Recently, I had been eyeing a used CBR250R bike as a small, light runaround bike, but most are in the $2500-3500 bracket. With fuel injection and all the modern conveniences, the new 250s achieve some 70+mpg mileage figures, which can certainly save some $$ these days. It will be interesting to see if my 90 mpg figures at the economy run will fall very far down with modern gas, with this machine still being fueled by a conventional 32mm carburetor. If it proves to be reliable and fun, with good mileage, the CB250RS may stay in the stable for awhile, this summer. It’s nice to have my old friend back again.

Bill “MrHonda” Silver

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