Honda CB500F Rebuild Part 8 - Carburetors And Exhaust

The final parts of the rebuild were the intake and exhaust systems. I prefer round slide carburetors to vacuum carburetors, so I purchased an incomplete set from eBay. I completely rebuilt them only to discover that Honda had they have a different center-to-center spacing then the engine I had installed.

Apparently, when Honda switched the CB650 from slides to vacuums, they changed the spacing of the cylinder head intake runners, rather than modify the carbs. I decided to disassemble my set, fabricate custom piping and brackets, modify the throttle and choke linkages, and respace them to match the head.

Disassembly Begins

Grinding clearance into the carb bodies

Custom crossover piping

Narrowing a factory fuel fitting

Drilling new holes in the throttle linkage

I modified a set of spacers from the later vacuum carbs to lock the rack together.

Finally, I fabricated a new exhaust system. An aftermarket 4 into 2 CB650 exhaust will not clear the footpegs on a CB500 frame, so I purchased several rotten sets of original CB650 pipes. A few weeks with a hacksaw and hand file, as well as a pair of stainless 2 to 1 pipe fittings, and the bike was complete!

Honda CB500F Rebuild Part 7 - Seat

After refinishing the tank, I turned my attention to the seat. The foam cushion had completely disintegrated, and the pan was suffering from serious rust, so I started by removing the cover and disassembling all the parts

 

Cover removed. Not too bad....

Nope, that's beyond saving

As suspected, the foam was totally ruined. Luckily, the pan was still solid and hole-free, so I sent it out for sandblasting and powdercoating. Meanwhile, I began searching for a suitable replacement cushion.

Unfortunately, I was unable to find an aftermarket cushion for an early CB500, but after some research I determined that an early CB750 cushion could be modified to fit. I purchased one, carved out a relief in the underside to clear a hump in the pan, and shaved down the front to match. I then attached it to the pan with rubber cement.

 

 Finally, I installed a replacement cover, and lined the edges with self-adhesive flexible chrome detail edging from the auto parts store.

Honda CB500F Rebuild Part 6 - Gas Tank

After rebuilding the rolling chassis, I started refinishing the bodywork. The gas tank and seat both required extensive repairs, and took several months of careful work to complete.

First in line was the fuel tank. My brother had designed and applied the original custom paint job in 2005, and the years had not been kind. Chips, gasoline spills, and a failed attempt at stripping the interior KREEM coating had left the paint faded, stained, and damaged by solvents. I removed most of the old KREEM coating, followed by several days of careful wet sanding, as well as compound polishing by a much more patient friend of mine. I then touched up a few chips by hand, waxed it, and installed a new petcock.

 

Honda CB500F Rebuild Part 5 - Reassembly Begins

The first stage of the reassembly process was build-up the rolling chassis by reinstalling the engine, major suspension components, wheels, and bodywork on the frame.

During this stage, I upgraded the bearings on the front and rear suspension, used brand-new flanged grade 8.8 hardware, and replaced the original high handlebars with Euro-style low bars.

Honda CB500F Rebuild Part 4 - Teardown, Gathering Parts, And Modifications

I left the bike in the back of a friend's garage for over a year before revisiting it. At this point, she was a complete mess. The original rebuild was nearly a decade old and had not held up well. Because of my low budget and inexperience in high school, many worn-out parts had been reused or poorly fixed. Ignoring the wrecked engine, the rest of the bike was almost unusable.

The rattle-can paint had flaked and the entire frame required a full repaint. The seat foam and cover were disintegrating, many parts were rusting, the charging circuit barely worked, the suspension bushings were worn....the list was endless. Basically every piece needed attention.

The first step was a complete nut-and-bolt teardown, inspection, and locating the major replacement pieces.

 

At this time, I decided that the original engine was beyond saving, so I began looking for replacements. The CB650 SOHC from the early 80's was the final evolution of the orignal 1971 CB500 block, and used identical dimensions and bolt patterns, so I decided to upgrade the power and reliability, rather than returning to stock. I was finally able to locate a replacement engine in western Maryland, and road-tripped with my grandfather to recover it.

The CB650 engine will "just" fit into an unmodified CB500 frame, but the underside of the frame backbone needs to be slightly shaved in order to remove the middle valve cover for maintenance.

Finally, I had the frame stripped and professionally powder-coated, and could begin reassembly.

 

Honda CB500F Rebuild Part 3 - Changing Styles

The bike went through a few style revisions during its first year. After the initial rebuild, it sported a bobbed front fender, but was otherwise stock.

 

However, during my first NYS inspection, this fender was declared unsafe. Its next revision included a full fender, three headlights, and a handmade fender plate.

The extra headlights were quickly removed when I discovered that the charging circuit could handle the extra amperage. Then, in 2009, a pickup truck pulled in front of me, wrecking the fender, forks, and headlight.

 I rebuilt her the following winter, but did not replace the fender plate.

 

After this, the bike soldiered on for 4 more years, as the engine developed numerous unsettling rattles and knocks, and began to burn concerning quantities of oil. Finally, during a tune up in preparation for a ride to the 2013 Thanksgiving Parade, the cam chain tensioner adjuster broke. It was able to grind, scrape, and knock to Manhattan and back, but it was clear that the original motor was completely spent. I drained the fluids and placed the bike into storage, while figuring out the next step.

Honda CB500F Rebuild Part 2 - High School Tinkering

When I started rebuilding this bike (the first time!), I was heavily influenced by the Custom Bike craze on Discovery Channel. I watched American Chopper and Biker Build-off constantly, so I knew that the bike had to be customized.

Years under a ripped tarp had taken their toll, and the paint was pretty much shot. I disassembled the bike and stripped it to the bare metal, then I repainted it red with metallic blue flames. My brother created the flames by hand, drawing their shape with thin tape and masking it off for the high-end rattle can job.