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Discussion Starter · #1 ·
1980 CX500



Rebuilt the carbs, although they were immaculate when I pulled them apart so they didn't need much cleaning. The bike starts right up but it just will not stay running without the choke pulled. It responds to throttle input just fine and if I give it a little bit of gas it will stay running without the choke.



Some other things that may help: one cylinder seems to be running a lot hotter than the other judging by exhaust temp. I'm also getting slight backfires/sputters out of the exhaust. I know the gas is clean and I have a fuel filter on it.



Any ideas? I tried adjusting the idle with the screw but it doesn't seem to do anything. I'm stumped!



I should also add that I never had the bike fully running. I bought it in this condition. I rebuilt the carbs because when I bought it one of the bowl gaskets was leaking like crazy.
 

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1980 CX500



Rebuilt the carbs, although they were immaculate when I pulled them apart so they didn't need much cleaning. The bike starts right up but it just will not stay running without the choke pulled. It responds to throttle input just fine and if I give it a little bit of gas it will stay running without the choke.



Some other things that may help: one cylinder seems to be running a lot hotter than the other judging by exhaust temp. I'm also getting slight backfires/sputters out of the exhaust. I know the gas is clean and I have a fuel filter on it.



Any ideas? I tried adjusting the idle with the screw but it doesn't seem to do anything. I'm stumped!
hi formz,and a warm welcome from spain.first things first.put your bikes details and your location into your signiture line.



if you are happy your carbs are lean....sweet

because you need choke,it sounds as though you have dirty carbs.but,

...your last line says something else.idle screw is the only big black knob,yes?located between and under the carbs

winding it in or out does nothing,is that what you are saying?
 

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Discussion Starter · #3 ·
hi formz,and a warm welcome from spain.first things first.put your bikes details and your location into your signiture line.



if you are happy your carbs are lean....sweet

because you need choke,it sounds as though you have dirty carbs.but,

...your last line says something else.idle screw is the only big black knob,yes?located between and under the carbs

winding it in or out does nothing,is that what you are saying?
Correct it doesn't seem like the idle screw is adjusting the idle at all. I should mention that is difficult to even tell since I have to hold the choke open or blip the throttle to keep it running. I'm not sure having the choke open and adjusting the idle screw is a productive measure or not.
 

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It sounds like you have an air leak,,probably on the side that is running hot.

Is there a good oring between the head and the intake manifold?



You can locate air leaks using an unlit propane torch and moving it around the joints between the carbs and the manifolds and the manifolds and the heads,,if you hear a difference in engine speed when you put the torch in an area, there is a leak.
 

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Discussion Starter · #5 ·
I forgot to mention that I bought brand new insulators (carb boots/elbows) from honda and replaced the gaskets that go to the heads as well so there shouldn't be any leaks anywhere past the carbs. (Hopefully!)



I removed both idle jets when I rebuilt the carbs and they were spotless, too.
 

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Still would not hurt to check for leaks.



Did you check the air cut-off valves?
 

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Did you separate the carbies when you rebuilt them? If so, they MUST be syncronized so that they work together as one. This COULD be A reason one side is running hotter than the other, and a very GOOD reason why the bike won't idle.



To start working on the idle mixture screws, turn them inwards to "lightly" seat them, and then turn out 2 1/2 turns. This SHOULD keep the motor running so that you'll be able to "fine" tune each carb. IF those aluminum caps ON the idle mixture screws have like a "wing" on 'em? These should be cut off to help fascillatate your fine tuning, as they were added onto these bikes sold in America per E.P.A. guidelines (at the time) and are no longer needed.......not to mention making it QUITE a Pain in the backside when adjusting...lol.....For as you have probably already noticed, there are 2 "restricting" lips one either side of the idle mixture screw on the bottom of each float bowl, that was SUPPOSED to limit how FAR you could adjust each screw. But, without that corresponding "stop" tab on the cap?.......No problemo amigo...........lol



Hope this helps.
 

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Discussion Starter · #9 ·
Thanks for the reply. I did indeed separate them when I rebuilt them. I was going to synchronize them but couldn't get it idling so I haven't gotten to that step yet. I replaced the idle mixture screws as they were included in the rebuild kits with versions that don't have that little wing on them so I can turn them to my hearts content! When I put the carbs back in I remember seating them then turning them out two turns, but its possible they may need to come out even more (or possibly go in??) to keep them running, correct? I will reseat them then turn them out again and see if I can get it running. Thanks for the tip!



This is a picture of the kit I bought:

http://i.imgur.com/UT3tl.jpg



The new mixture screw is (I think) on the bottom row, third from the right.
 

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Before doing that, methinks turning that big black knurled knob in between the 2 carbs to a point where the bike would STAY running without choking or blipping the throttle, would be the first point of order I would address. Because FOR SURE ya can't sync or adjust anything, IF it won't stay running.



The idle speed can ALWAYS be set lower (or higher) AFTER the carbs are synch'd.



I think the carbs should be synced at idle, but think a running up the rpms and checking is in order. Some say at idle...some say at a higher rpm as this is where you'll be running most of the time, maybe adjust to some point between the 2?...er even if that is possible?



Hope this helps ya there.





Oh ya, you can probably put those caps on (minus the wing) as the replacement screws are just a knurled brass end with a slot. Makes it easier to adjust by hand rather then trying to angle a screwdriver in a tight space.
 

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Another possibility for it not idling would be if the tips of the idle mixture screws broke off in the carb body, blocking the idle port in the throat of the carb.



This has happened before,see this thread ,some of the rebuild kits parts are not exactly the same as the OEM parts and when you tighten the idle mix screws to seat them they jam in the holes,,when you back the screws off the tips break and stay lodged in the holes.



You could take the screws out and have a look at the tips.
 

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Discussion Starter · #12 ·
Well the problem I have with the idle adjustment knob is that it doesn't seem to want to adjust anything! I'm not sure which way to turn it but I turned it many rotations in both directions to seemingly no difference in idle quality. The official honda manual and the haynes that I have both just say "turn it" and don't mention a direction, or how many rotations it should approx take. Any ideas?
 

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Well the problem I have with the idle adjustment knob is that it doesn't seem to want to adjust anything! I'm not sure which way to turn it but I turned it many rotations in both directions to seemingly no difference in idle quality. The official honda manual and the haynes that I have both just say "turn it" and don't mention a direction, or how many rotations it should approx take. Any ideas?


You turn it in(as to tighten a screw) to increase the idle.



It should not take much,,
 

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You can remove the tank and look at the business end of the throttle adjust screw and see that it pushes against the throttle arm or whatever it is called. Turn it clockwise.The part it hits is the part that moves when you twist the throttle.
 

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A rule of thumb: "Righty-Tighty...Lefty-Loosey" If yer turning it to the right it SHOULD, eventually start hitting the throttle lingage. Is pretty finely threaded, so if 3 er 4 twists ain't gettin it? Keep a twisitn'. If you look up under there, you should be able to see where the end of that bolt hits the linkage and give you some idea as to how far ya have left to go.
 

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Discussion Starter · #16 ·
Awesome guys thanks for the great tips. I'm going to remove the tank and make sure its hitting the linkage. I'll update this thread next weekend when I can get back to the bike. You guys have been great.
 

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Glad to share what little knowledge I have acquired in the 4 years I have had mine. I just hope it GETS YA UP N RUNNIN'........LOL
 

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There IS a way to do a "manual" sync of the carbies, but think they needs to be off the bike to accomplish (not sure though), using a feeler gauge to bring them in to a "reasonable" sync, and fine tune it after ya get her running.
 

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keep us updated on what you find, i am have in carb problems too and will be following this to see if any ideas turn up for my problems. I feel like i have taken these silverwing carbs off and on about a zillion times... i just ordered an ultrasonic sink from harborfreight so that is my next step.
 

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Discussion Starter · #20 ·
There IS a way to do a "manual" sync of the carbies, but think they needs to be off the bike to accomplish (not sure though), using a feeler gauge to bring them in to a "reasonable" sync, and fine tune it after ya get her running.
i have one of the fancy fluid filled carb sync gauges so I'm not worried about trying it other ways.
 
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