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I recently picked up a 1980 Honda CX500 Custom in pretty decent shape. I had to clean up the carbs and get the right-side needle unstuck, but it seems to run just fine.

However I was wondering about carb settings to bring the idle speed up. Right now it tries to idle at about 500 RPM and quits. Stock idle should be about 1100 I believe. I set both idle speed screws (on the botton of the carbs, I hope they're idle speed screws) out one turn. Any idea of the factory settings? Should I just keep screwing the screws out until I get a satisfactory idle?

I'm totally new to shaft drives, any tips there would be helpful. Doesn't seem to be anything wrong with it and I'd like to keep it that way.

Are the official factory service manuals really any better than a Clymer manual for example?

Thanks in advance.

cant really go wrong with a factory manual...... its made by the people who make the bike...

NorthernPete wrote:cant really go wrong with a factory manual...... its made by the people who make the bike...

That's exactly what I was thinking, for only a couple dollars more.


A couple other things I thought I'd mention after reading through the forums a bit..... the valves don't tick. The motor so far is rock-solid throughout the powerband. It has 43146 miles on it, no idea if the odometer has rolled around.

My main issue is the idle. I didn't want to toy with the screw on the bottom of the carb too much in case it isn't an idle speed adjustment. I assume it is since it is the only adjustment screw I can see and the sticker on the frame says "No adjustment" for everything carb-related except idle speed.

Idle speed screws change the position of the slides or throttle butterflies to let more air in at idle. Normally, when you back the screw out, you are putting less air into the bike. If the bike runs better with the screws all the way out, it means you have a lean running problem at idle - your idle circuit in the carbs still are dirty. There is more to the carb than just the jets - a bunch of little passages for air and fuel to mix - these get filled w/ crud that's hard to clean.

All of the above is assuming you really are using the idle speed screws. It's also possible that a PO disabled the factory stops on the Idle mix screws and THAT'S what you are playing with. In this case you are increasing or decreasing the maximum amount of fuel/air that goes into the carb at idle. This is preset at the factory and shouldn't be touched - usually owners start messing with this to clear up rough idle symptoms, instead of cleaning the carbs like they are supposed to. This can lead to a world of problems for people who inherit th e bikes **like you** because not only is the bike out of spec for the idle mix, but it's also got 20 years of crud that has cemented itself inside the carbs because of laziness.

Since you don't know what you are playing with, I would wait til you get your manual. The Manual will tell you the factory preset for the Idle Mix screws and also tell you which screw is which. In between then and now it wouldn't hurt to pull the carbs and make sure they are extra clean. Then when you have the manual, you can also adjust the valves and synch the carbs so the bike runs optimally.

[quote="TechTMW"]
All of the above is assuming you really are using the idle speed screws. It's also possible that a PO disabled the factory stops on the Idle mix screws and THAT'S what you are playing with. In this case you are increasing or decreasing the maximum amount of fuel/air that goes into the carb at idle. This is preset at the factory and shouldn't be touched - usually owners start messing with this to clear up rough idle symptoms, instead of cleaning the carbs like they are supposed to. This can lead to a world of problems for people who inherit th e bikes **like you** because not only is the bike out of spec for the idle mix, but it's also got 20 years of crud that has cemented itself inside the carbs because of laziness. /quote]



My thinking exactly.

Hi there, the two screws on the bottom are your air/fuel mixture screws. what you want to do is seat them in all the way but DONT TIGHTEN!! Back them out two full turns and strart your bike, it should run ok, if it idles low there is a idle adjustment screw in between the two carbs more on the left side. It should have a black round handle on it. Counter clockwise is idle up and clockwise idle down. i will scan my manual for you on how to do it incase your confused. I have a 1980 CX500 as well and just got it running right adjusting the carbs, valves and a few other things. Im no expert but i do know this bike very well.

well, I've made some progress, and I've continued this thread detailing a specific problem here:

viewtopic.php?p=104929