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Discussion Starter #1
Hi. My 500 TC is running very rich at cold startup, but better when it warms up.
I have removed the air bypass valve and everything seems to tjeck out. It has a slight bypass when i try to blow through the hose coming from the air throttle box, and the reeds block the air if I try to suck through it the other way.

I don't quit understand how the valve works. I can see that the cooling water runs through the valve, so expect it should close when the water warms up, but what is the electrical connection for and how does it open fully at cold ?

Thanks
 

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Ok, so Here is what I know about this issue. The purpose of the air valve is NOT to control fuel mixture when cold. It only controls additional air to bypass the throttle blades during warm up allowing increased idle speed. That's it. The wire is powered directly from same circuit as the fuel pump. It heats a bimetal spring which closed the air after time elapsed. This is how your bike starts, idles high, and slowly comes down to base idle as it warms.

The air/fuel ratio is another story. These are VERY crude systems remember. The injector pulse width is based on what Honda has in the computer table for warm up. There is no feedback circuit, oxygen sensor, etc. The engines ALWAYS ran very rich cold, and even slightly rich when warm. We are stuck with this with one exception- the Suzuki/Toyota sensor mod which replaces our crappy Nippendenso sensor. This commonly called a MAP or Manifold Absolute Pressure sensor on most systems. Honda calls it the Pb sensor for our bikes. Most everyone has raved about the increased rideability of the bike after this mod and it does remove some of the rich/cold stumbling inherent on these bikes. See link below.


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Discussion Starter #3
Thanks for the answer, Does the cooling water Bypass take over for the electrical Bimetal heater at one point, or how is that to be understood ?
I have a complete throttle body from my parts bike, so I will try and replace the whole thing including the injectors ans see what happens. The 650 TC is sooo much simpler with manual operated fast idle.
 

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Actually - The air valve is controlling your fuel/air mixture.
Crude- yes.. the computer richens the mixture when it is cold. However, you need more air, so … you have the air valve. For cold start up, the computer gives the bike more fuel, and the electric/coolant valve gives the bike more air. The air valve is combination of a bi-metallic strip/ and electric assist.

650T has no such luck...

If your strip is wore out in the valve, it won't twist like originally designed. However, if you look on the valve, you will see a dab of sealant. Remove the sealant and you will find a nut. If you loosen the nut you will find the it sits in a slotted housing. You can then rotate the stud/nut and tighten back down. This counteracts the age. You will have to figure out the best position of the rotated valve for cold starts. It will then work like new again.

PK
 

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Discussion Starter #5
Good information - I removed The Valve cover on both my units an the Slider is allmost closed In Cold condition . I assume they should be fully opened - and then close when Hot ?
Also - what should the reIstance read on The bimetal conector ?

Thanks :)
 

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Good information - I removed The Valve cover on both my units an the Slider is allmost closed In Cold condition . I assume they should be fully opened - and then close when Hot ?
Also - what should the reIstance read on The bimetal conector ?

Thanks :)
Unless someone has a known good one out to measure, Honda never published specs for this in the manual. Post some pictures of your mod that Pete described,
 

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Discussion Starter #8
So had a little time to play with the valve today .
The valve was completely shut at cold so i tried to adjust the valve body, as PK suggested, but i could only get a slight opening. The little stainless spring is surprisingly strong and kept pushing the bi-metal the other way.

The unit from the parts bike was much better, and after adjusting it and slightly loosing the spring i got full opening at cold and it slowly shut it self to 20 % opening when applying 12 V to the connector . The closing time was near to 10 minutes. A little heat on the housing to simulate the hot cooling water made i shut all the way .
I think its good now and I'm excited to get it back in the bike again .
The Resistance on both units waseading 98 Ohm - so the heating element is very small ( 1.5 W)

Adjuster screw stripped from 38 year old silicone (7 MM hex-head )
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Cold condition after adjustment
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8-10 Minutes of 12 v
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MDO
 

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Discussion Starter #9
Got the whole thing back together incl. new Ignition sensors and water seal.
What a different bike. Cold idle starts at 2100 RPM and slowly drops to 1100 as the motor warms up Before the bike was misfiring due to the rich mix until i got warm, now its just start and go.
A job worth doing.
 
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