Honda CX500 and Variants – Additional Carb Fit Details

This information is courtesy of my good friend – the late Dick Smith (aka Dick in Raleigh) – who was a noted CX500 expert.
  

This information is courtesy of my good friend – the late Dick Smith (aka Dick in Raleigh) – who was a noted CX500 expert.

Scroll to the bottom for help in determining whether or not you have an accelerator pump! (See: picture in comment section.)

1978-1979

CX500 Standard. No accelerator pump. Fuel hose input on outside of left carb. Pipe with o-rings between carbs. Adjustable floats.

1979-1980

CX500 Custom and Deluxe. Fuel hose input moved to brass pipe between carbs. Some with accelerator pump, some without. Some may have adjustable floats.

1980

Standard removed from Honda line, replaced with Deluxe model.

1980-1981

CX500 Custom and Deluxe. With accelerator pump. Extra pipe between carbs for accelerator pump output. Vacuum port added to 1981 right carb for petcock. Fixed non-adjustable plastic float. Nonadjustable mixture screw.

1981

GL500 introduced (SilverWing) Fuel hose input moved back to left carb. Carbs are closer together than on early CX500. Piping between carbs is same diameter as CX.

1982

CX500 Deluxe removed from Honda line.

1982

CX500 Custom Accelerator pump, center fed fuel, with vacuum port (considered the best set to buy)

1982

GL500 no changes.

1983

GL650 & CX650 Only changes were to jet sizes and mounting method. Carbs are angled not parallel and have complex CBX style throttle links.

Other:

• CX500 Fuel line inputs were moved due to the bike tending to start on the left carb only when parked on side stand. Center fed helped but didn’t eliminate the problem.
• Accelerator pump added due to the bike stumbling off the line. This improved off-idle response.
• GL500 Carbs are spaced closer together. Not enough room for center fed.
• GL650 & CX650 carb mounting and different air box made the carbs difficult to mount parallel to each other. They are mounted with the outputs farther apart than the inputs. Requires complicated mechanics between carbs.
• All variants have rubber blanking plugs over the idle jet access.Early CX500 carbs (without accelerator pumps) use the same rubber blanking plugs as used on some CB750, CB900 and CBX models.
• Later CX500s (with accelerator pumps), all GL500s and all 650 models use similar rubber blanking plugs, but these have a slightly larger diameter. The plugs required for early CX500s are too small and WILL NOT WORK in these carbs!
• All variants have 2 main fuel jets: primary main and secondary main (both removable)
• Some variants have non-removable idle jets.
• All 650s have removable idle jets.
• The “non adjustable” EPA-mandated idle mixture screws on later versions can be reworked 3 different ways.Remove the tang on the bowl with a hack-saw
• Remove the tang on the screw.
• Carefully heat the limiter cap with a soldering iron and gently pry off the cap.
• Broken idle mixture screws can be saved by making a sharp hack saw cut straight down into the brass. Thus creating a new screw head slot. Note: do not cut too deep into the carb body. If you do, you will have a very nice aluminum paper weight instead of a carb body! Soak in penetrating or sewing machine oil and the mixture screw (nearly) always comes out. Stubborn cases may benefit from the careful application of heat from a pinpoint torch. This helps loosen fuel varnish. The slight hack saw into the carb body is a draw back from a restoration point of view, but a good tradeoff all things considered.
• Idle mixture screws on GL1100, CBX, CB500 and CM400s are all the same.
• There are 3 variations on the air-cut off valves. Even thought the OD of the diaphragm is the same for all 3, they do not interchange as there are differences in the actuating pin and spring.
• There are 2 variations on the accelerator pump. These do not interchange.
• Float pivot pins same as GL1100 / CBX.