Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: Morala on December 23, 2024, 07:40:09 PM
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Hi everybody as in previous posts i am a new owner of a 1974 550 and i am still learning a lot about the bike, what i find at the moment is sometimes when i start the bike it revs very high about 4000 revs for a short time then settles down to normal tick over, do i need a complete carb strip down or is there a simpler solution any advice greatly appreciated thanks again.
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How much choke are you using when it's revving high?
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Hi taysidedragon no choke on so not sure if its a fuel problem, since i got the bike i havent touched the carbs, took the tank off and cleaned the inside of tank and checked the filter on the fuel cock, never had a 4 cyl carb bike before so not sure what to check.thanks for your reply.
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just to add to my previous post i changed all the filters and fluids but didnt touch the plugs as they seemed to be new
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http://www.sohc.co.uk/index.php/topic,31510.0.html
You might find the above link relevant it's in the Anoraks Corner section, quite a lot to read, some call it a hanging throttle, at it's core is the carb synchronising starting point generally being the bench synch.
Before rushing into taking off the carbs I would want to check a lot of other things first. e.g. Are the throttle cables working correctly, is timing spot on for 1/4 & 2/3, no air leaks on the induction side, valve clearances, standard air cleaner set up, advance retard working, right plugs etc.
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This can be very frustrating, I've still not solved my hanging idle but as Ted says go through all of the simple things before you do anything drastic.
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Hi, Morala.
For clarity, does this situation persist after the bike has warmed up? In other words, do the high revs persist when the engine is warm and you blip the throttle? I ask as your original explanation seems to suggest that the high engine revs are a temporary situation that self resolves after a short while?
The guys discussing a ‘hanging idle’ are describing a situation where the engine fails to return to a normal idle speed after blipping the throttle. If this is the condition you are experiencing and nothing else has been changed (eg new throttle cables) and the throttle slides snap closed, I suspect that the idle jets are obstructed.
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As the bike is reving very high at initial start up my first suspect would be the fast idle adjustment on the carb rail. It sounds as though it has been set very high negating the need for the choke to be used. If this does prove to be the case there will be a reason why the fast idle has been set so high, this could be blocked pilot jet circuits in the carbs (stale fuel gone off in the drillings etc) or poorly adjusted cables.
start with easy to see and adjust items first before tearing the carbs apart although it does sound as though the carbs wil need a good clean and inspection once you have found the initial problem. If you do strip them try and use the original brasswear where you can. Nurse Julie on here sells the fuel resistant viton O-Ring kits you will need.
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500 and early 750 dont have a fast idle, only the K3
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That's interesting Bryan. Is this the model where one carb slide is set and the others are adjusted to match? How is fast idle set on these models?
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That's interesting Bryan. Is this the model where one carb slide is set and the others are adjusted to match? How is fast idle set on these models?
There is no 'mothercarb' on these models; all 4 can be adjusted. There's no fast idle either. A raised idle is achieved either by manually opening the throttle somewhat, as explained in the Owner's Manual or temporarily adjust the big idle speed screw for this. The latter needs to be dialed back ofcourse once the engine is warmed up.
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Cheers for all your advice, thinking of striping the whole carb down as i don't know what the previous owner has done to the carbs regarding cleaning and setting of them, will start there and see what happens then i can take it from there again thanks for all your advice
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Good idea. Keep us informed of your progress please.👍
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Cheers for all your advice, thinking of striping the whole carb down as i don't know what the previous owner has done to the carbs regarding cleaning and setting of them, will start there and see what happens then i can take it from there again thanks for all your advice
I have always managed to do all maintenance on these carbs by just removing the floatbowls and the parts in there. Never had to separate the carbs from one another.
Back then practically nobody changed the position of the jet needles. No one did that. Jets, floats, all can be removed easily. Cleaning can be done with a straw on a carb cleaner can. I never needed ultrasonic baths.
What is posted nowadays, has a lot to do with itchy hands.
Oh... and make sure the ignition is fine. Some 90% of the fuel problems turn out to be electric...
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Is carb cleaner really enough for carbs that have dried fuel in the galleries
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I would say not. My carbs were well and truly plugged with varnish and no amount of carb cleaner would clear them. I had to resort to using an ultrasonic cleaner used in conjunction with Allan’s solution at 60deg C along with some judicious probing with a guitar string in the idle jets and passages. Result….perfect idling and throttle response. This thing can actually tick over at around 500 rpm!!!
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They can but by christ the primary rattles if the carbs are slightly out, i always used900 to 1000
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Regarding the passages, I've never really known which ones should exit where to know I've definitely cleared them. Some are obviously blanked off, is there a diagram anywhere detailing the routes?
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They can but by christ the primary rattles if the carbs are slightly out, i always used900 to 1000
I know. I was simply suggesting that proof of a healthy, well set up motor is its ability to tick-over at very low revs. My optimal idle speed (quietest) is actually 1100rpm.
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Regarding the passages, I've never really known which ones should exit where to know I've definitely cleared them. Some are obviously blanked off, is there a diagram anywhere detailing the routes?
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Trick here is to use your fingers, blocking off two outlets of the three at any one time. I’m sure there is a diagram somewhere. I used it to identify the circuits in order to force fluid through the passages.
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Regarding the passages, I've never really known which ones should exit where to know I've definitely cleared them. Some are obviously blanked off, is there a diagram anywhere detailing the routes?
Maybe this helps. From 08:30 on in: https://www.youtube.com/watch?v=iXD7F4q72M4