The Honda air valve (auxiliary air regulator) was designed to aid cold starts and automatically regulate fast idle speed during warmup. The design includes an onboard heater, coolant passages and a bi-metallic actuated gate valve to accomplish these tasks. This is a “dumb” device with no sensors and no communication with the ECU. It’s similar to the auxiliary air regulators found on many 70's vintage automobiles with early Bosch EFI systems.
The Honda air valve is no better than the Bosch components Honda copied. It’s unreliable and prone to erratic operation and failure. My own CX500 Turbo received a very comprehensive restoration with quadruple bypass. When I started riding, I discovered that my air valve was toast. The heater element was burnt out and the gate valve was seized closed. Luckily, I managed to find a NOS Honda air valve from CMS in the Netherlands …the very last one in inventory. It lasted only a month before it quit working correctly.
I decided there had to be a better answer and I’ve found one - a MANUALLY controlled air valve. I made this discovery while searching obscure automobile forums. It seems that the Alfa Romeo GTV6 & Milano community had already dealt with and resolved the same issues decades ago on similar balky air valves.
My conversion is on the road and working beautifully, I now have a “choke” knob that gives me full control over warmup activities.
Depending on the weather - with the knob fully “out” (air valve “open”), I initially got about 2,900 rpms when I made a cold start ...a bit fast. I included a "cable stop" on the pull cable so I could adjust max. cold start idle speed. After adjustment of the cable stop, I now get about 2,200 rpms on a cold start. This closely matches what Honda intended and is ideal.
Within a few seconds, I can push the knob in to about half-way for a warmup idle of about 1,600 rpms. After 5 minutes or so of riding, I can push the knob all the way in (air valve closed). When fully warmed up, I now have a steady and reliable curb idle of 1,100 rpms …also ideal.
There were several options on where to mount the new manual air valve, but my selection worked out to be the best compromise. This location provides: simplified plumbing, a dedicated filtered air supply, linear alignment with the “choke” cable for reduced cable friction, ease of maintenance and decent weather protection.
Fun fact: Honda actually admitted defeat on their own poor design. For the 1983 CX650 Turbo, Honda eliminated the air valve and bypass air circuits altogether. Instead, they added a simple “choke” lever that “cracked” the throttle valves slightly for cold starts. I investigated using this brutally simple strategy, but it was actually more complex and expensive than my solution and required CX650T parts that are very scarce and valuable to CX650T owners.
Material List:
- Cable operated manual heater control valve (without by-pass) such as: Carquest #74627
- Dorman #03787 - heavy duty, 5 foot push-pull “choke” cable (with stiff inner wire) or similar: Advance Auto # 03787 (no "choke" symbol knob) or ...
- 237 Rotary Universal choke cable #290831 - 63" inner (with "choke" symbol knob)
- Small crankcase vent air filter with 15mm OD outlet.
- 3 feet of 12mm (1/2”) ID silicon hose (reed valve to air valve)
- 5 feet of 4mm ID silicon hose (to cover outer choke cable housing)
- 2 feet of 6mm ID silicon hose (water pump by-pass circuit)
- 1 foot of 8mm ID silicon hose (reed valve to intakes)
- 1/2” x 1/2” barbed elbow
- Miscellaneous clamps, hardware and zip-ties.
Installation Notes:
(Refer to the photos for additional details)
- Remove dash panels, side covers, seat and fuel tank.
- Remove the Honda air valve.
- "Seal" the Honda air valve 12V connector with electrical tape or a short section of shrink wrap tubing (preferred). This will protect against potential short circuits as this conector is "hot" whenever the fuel pump is running.
- Remove the original hose that feeds to the bottom of Honda air valve. Plug the outlet for this hose near the surge tank / throttle valve assembly.
- Remove the coolant tubes for the Honda air valve.
- Run one 6mm ID hose from the water pump outlet to the thermostat housing. This will be “finger-to-finger” in the photos. The function of the by-pass hoses was to heat the air valve. My method effectively “bypasses the bypass” and reduces the chance for a leak.
- Retain the reed valve assembly. Make sure the hoses from reed valve assembly to the intakes are in good order. I recommend replacement with high quality 8mm ID silicon hoses. The reed valve assembly protects the new air valve from ever seeing “boost” pressure. It could easily handle the pressure, since it was designed to handle pressurized, heated coolant. But, the reed valve eliminates the unnecessary chore of pressurizing the extra volume in the hose to the remote air valve.
- Unlike the original Honda setup, the independent air supply for the manual air valve also isolates it from “back boost.”
- Mount the manual air valve near the tail on the left side as shown in the photos. I fabricated a bracket that is approximately 1” x 4” that attaches to the valve and mounts to the bike using the seat attach bolt.
- “Tweak” the bracket as necessary to make sure the valve’s lever does not foul on anything.
- Run a 12mm ID silicon hose from the reed valve assembly to the new air valve using the barbed elbow as shown. Make sure hose takes a path with gradual turns and no “kinks. Silicon hose is recommended because it provides a “snug” fit to the 12mm reed valve assembly and enough flexibility to stretch onto the 15mm air valve. Don’t use ordinary automobile “heater hose.”
- Observe the directional arrow on the new manual air valve. It will work in either direction, but has more precise control at 1/2 choke or less if you mount as shown.
- Depending on your supplier, your may have to reverse the cable attach bracket and “re-clock” the lever to match my photos.
- Install the 4mm ID silicone hose cover on the outer cable housing. This is imperative since the cable will travel near the battery and needs isolation from the battery posts. This will also protect the paint on your frame, etc. and prevent rattles.
- Remove the inner cable and thoroughly lubricate the cable housing with high quality cable lube.
- Install the new throttle cable. Take care to pick the most gradual path you can chose with NO SHARP BENDS. You will probably need to trim the overall length of the cable a bit. MEASURE TWICE and CUT ONCE! Use cable cutters (available at any bicycle shop) to get a clean cut with no burrs. Leave the inner extra long. This will give you extra leverage later, when you form the cable end "eye."
- SAFETY ALERT: Make absolutely certain that your new “choke cable” does not interfere with the handlebars or controls as the bars swing “lock-to-lock.” Check with the knob pulled out about 2 inches.
- Slide the cable stop onto the iner cable. This will allow you to adjust max. warmup idle speed.
- Install the air filter as shown above. Check for clearance and adjust as necessary. It’s OK to shorten the air valve’s inlet by 1/4” or so if you need a bit more clearance.
- Measuring and marking carefully, form an ‘eye” with the stiff inner wire (as shown) to attach to the valve’s lever. This eye needs no additional hardware or support to stay attached to the valve.
- I use 2 sets of vice grips and a suitable screw or nail to form the "eye" as shown in the photos below.
- Trim the excess inner wire, lubricate the valve's lever post and install the "eye" onto the post. Secure the outer cable to the bracket making certain that the valve is fully closed and the choke knob is all the way in.
- Your installation should look like this.
- Install the tank, dash panels, seat and side covers.
- Start the cold engine with the knob fully out and the cable stop "loose." Observe the idle speed. You should see about 2,500+ rpms.
- Adjust the cable stop for a cold idle speed of about 2,200 rpms. This may take a bit of trial and error.
- If you have a "high" idle that is not reduced when you push the knob in - you have an air leak.
- If you have a "low" idle that does not increase when you pull the knob out - you have an air blockage somewhere.
Post note:
In the early 80’s, I owned a 1970 Volvo 1800E - one of the very first Bosch EFI Volvos. It was a terrific car, but the auxiliary air regulator nearly drove me nuts! It never responded well to the dozens of adjustments (and replacements) I threw at it. I sure wish I had known about this strategy while I owned that car!