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Discussion Starter · #1 ·
OK, fellow CX500 fans, I am afraid I must be missing something obvious...



I own a 1979 CX500, purchased for $400 10 years ago, my first machine, and one I will never let go of. Found it in this town, not far from where I live, in South Ogden, Utah.



It has been running steadily worse every year, so I finally decided to do some work on it yesterday.



Sorry for the verbosity of the post, but I know how frustrating it is to try to help without knowing what's been done, so here's what I did yesterday:



* Checked compression on each cylinder, read 110 on both, almost identical readings so I considered that good.

* Pulled carbs, separated them.

* Found missing O-rings(the little tiny ones) on the little side air circuit that helps actuate the vacuum needle valves. Replaced with O-rings from parts carbs.

* Cleaned both internal jets with carb cleaner.

* Checked for smooth operation of needle valves, choke, throttle.

* Cleaned both fuel fill circuits and the connecting fill tube.

* Checked float level.

* Found broken O-ring on LH intake head flange, replaced with a good fitting ring (not Honda - but fit perfectly)

* Reassembled carbs and reinstalled, being sure to get boots securely on, no leaks.

* Pulled air cleaner, tapped to clear loose dirt (running about 5000 miles on this air cleaner)

* Checked spark plugs, replaced RH plug (this was the most problematic cylinder before I began)

* Noticed RH plug wire was loose in the L-shaped boot; Cleaned corrosion on the pin inside the boot, cleaned the end of the wire, and re-inserted the wire. (Should this wire not be detachable? The LH wire is not detachable.)



After all that, the machine started up and ran, but was still stumbling somewhat. I warmed it up to normal operating temps, then:



* Adjusted idle to 1100RPM

* Leaned mixture on RH carb until RPM drop, then back 1 full turn.

* Adjusted back down to 1100 & repeated on LH carb, and final idle adjust back down to 1100 again.

* Throttle had hesitation, but otherwise the machine ran fairly smooth.



Took it for a quick road test, too much hesitation, then:



* Attached carb sync tool, adjusted sync screw until they were balanced. Was slightly off, but not bad.



After buttoning it back up, the machine ran better than it has in years. Great.



So this AM, after resting overnight, I pull the choke and it won't start at all. I get a stumble or two, but it's almost like the machine is dead. This is how it started out yesterday before all the work, so it could be that while it was warmed up, all the procedures and tuning I did went fine, but when the machine is truly cold there is still some sort of issue.



At this point, since I know compression is not an issue, and I am pretty confident the carbs are tuned about as well as they can be (at least by yours truly,) I'm starting to lean toward spark. However, I am quite weak in the electrics side of things - so what do you folks think?



Thanks in advance!



-Jim

1979 CX500 Custom

Ogden, UT



EDIT - Forgot to mention, I picked up a new battery last week, fully charged. The engine cranks over quickly.
 

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Jim:



Nice detailed post. You seem to have a good mechanical background.



Do you smell gasoline after trying to start when cold? How long were you cranking the motor? ASSuming your choke is working? ...I have no doubt as you seem to have the carb finess down pat. If no gas smell originating in the exhaust, then you could have a "gas to the carbs" issue, or gas to the motor issue.



This might include a petcock issue. Is your petcock a vacuum operated one, or gravity feed? - sorry, I should know, but often people have changed over the petcocks. If vacuum, then you may not be developing enough vacuum to "prime" the carbs when turning over using the starter motor. This is somewhat of an issue for many of us with vacuum petcocks, as the fuel in the carb bowl will dissapear after a day or so of non use and thus getting the fuel to the carbs so the motor can start can take awhile. You may wish to remove your air filter housing and spray in some carb cleaner. Aim for the throat of the carbs as this will provide a combustion source immediately, and if the motor fires up right away, you know you had a gasoline delivery issue. Once started, and the vacuum increases, ASSuming no vacuum leaks, it will pull in the gasoline and all should be well. And that's for a vacuum petcock.



If it's a gravity feed petcock, you may have a blockage in the lines. Have you cleaned the petcock? Are you running a fuel line filter. It's a good idea to do so after the petcock and before going into the carbs. Is your fuel tank clean?



If you smell gas after cranking, and you're sure it's getting inside the cylinder, ie, the gas smell you smell is coming from the exhaust, not dribbling out of the carb overflow valve, then it's potentially a spark issue.

You seem to have got the carb thing down pat. Have you done a stator check?
 

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Welcome to the forum, Jim. I see that you mentioned your location and the bikes model in your text, but if you would fill out your profile page and put your bike's model in the signature line, that will keep us advised of your model on every post you make.



Now, as to your bike. Did you remove the emulsions tubes below the jets when you had the carbs apart? How about cleaning the tubes below the "black banana" under the vacuum cylinder cap? These carbs are fickle about having all those tiny passages clean and clear. Oftentimes it takes multiple tries to get them clean. A ultrasonic cleaner definitely increases the chances you do a good job.



Since the bike doesn't want to start now, try spraying a burst of starting fluid into the air breather nozzle. A one second burst is plenty. Try starting immediately. If it fires up and runs for a few seconds, likely you have fuel problems rather than ignition. If it doesn't start, remove the plugs and hold against the frame, not the valve covers and crank. See if you are getting a blue spark at the plugs.



You mentioned checking the plug boots. Both should be removable, they screw off. When you get them off, use a flat bladed screwdriver to unscrew the slotted fitting inside the plug boot. There should be a rod, resistor, and spring inside. Often the resistor has turned to dust. Replace the resistor with a suitable length of aluminum, brass, or copper rod.
 

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Discussion Starter · #4 ·
Do you smell gasoline after trying to start when cold? How long were you cranking the motor? ASSuming your choke is working? ...I have no doubt as you seem to have the carb finess down pat. If no gas smell originating in the exhaust, then you could have a "gas to the carbs" issue, or gas to the motor issue.


No gas smell, and I only crank it four or five times per try. I like to keep starters healthy
It will sometimes fire on what feels like LH cylinder, sometimes both briefly, then die. Seems sporadic regardless of choke position, though it almost runs for a few seconds with the choke on.



This might include a petcock issue. Is your petcock a vacuum operated one, or gravity feed?
Gravity.



Have you done a stator check?
I see a note in my Clymer's manual to check for continuity to test the alternator/stator. Is this what you mean? Ohms less than infinity, basically?



I wouldn't rule out missing something in cleaning the carbs. I hate to go thru pulling them again, but I will if I missed something. I'm starting to wonder if I didn't get ALL the sludge (thought I had) and somehow the idle circuit(s) pulled in some loosened crud, post-cleaning & reassembly.
 

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Discussion Starter · #5 ·
Did you remove the emulsions tubes below the jets when you had the carbs apart? How about cleaning the tubes below the "black banana" under the vacuum cylinder cap? These carbs are fickle about having all those tiny passages clean and clear. Oftentimes it takes multiple tries to get them clean. A ultrasonic cleaner definitely increases the chances you do a good job.
What circuits are below the "banana?" I know what you mean, and I did NOT remove that.



Also, since I don't know what you mean by the emulsion tubes, I am going to say no, I didn't remove them... Is there a good reference online to understand the anatomy of these particular carbs?



I'll grab some starter fluid & try that. I'll also check the spark color, and check for the resistor as well.



Thanks for your help, I'll post when I try these things.
 

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Male sure that your choke plates are closing fully when you pull the choke knob out,,sometimes the spring on the shaft that connects the two will need an extra wrap on it.
 

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What circuits are below the "banana?" I know what you mean, and I did NOT remove that.



Also, since I don't know what you mean by the emulsion tubes, I am going to say no, I didn't remove them... Is there a good reference online to understand the anatomy of these particular carbs?



I'll grab some starter fluid & try that. I'll also check the spark color, and check for the resistor as well.



Thanks for your help, I'll post when I try these things.


In the top of the carbs there are four small venturi(Two under each ,"Black Banana".These are part of the idle low speed circuit and as stated the most common cause of carb problems especially at idle up to around 3,000 rpm.Over time they can be become clogged/restricted.



Several detailed carb cleaning threads here,



http://globalcxglvtwins.hostingdelivered.com/viewforum.php?f=19&sid=4687a7738aa5e67afd37ad1519fa79d0



Also a quick and worthy thing to aid starting is to clean/service the starter motor,



http://globalcxglvtwins.hostingdelivered.com/viewtopic.php?f=8&t=208



HTH
 

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Discussion Starter · #8 ·
In the top of the carbs there are four small venturi(Two under each ,"Black Banana".These are part of the idle low speed circuit and as stated the most common cause of carb problems especially at idle up to around 3,000 rpm.Over time they can be become clogged/restricted.



Several detailed carb cleaning threads here,



http://globalcxglvtwins.hostingdelivered.com/viewforum.php?f=19&sid=4687a7738aa5e67afd37ad1519fa79d0



Also a quick and worthy thing to aid starting is to clean/service the starter motor,



http://globalcxglvtwins.hostingdelivered.com/viewtopic.php?f=8&t=208



HTH
As far as I can tell, the spark looks yellow with blue highlights, much like my step daughter's hair. I'm ignorant at reading spark colors; should it be solid blue? After spraying the carb cleaner it still stumbled and died, like 3 or 4 good ignitions followed by stall. Pretty much the same.



It would make sense that the "banana circuits" may be clogged. It idles erratically and hesitates a lot at lower RPM.



The cheater in me wants to just pull those caps and spray the banana circuits with the carbs installed but I'm guessing that is a bad idea...
 

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Jim, I think you need to go back thru those carbs again too. The emulsion tubes are located below the jets. One will unscrew with a PERFECT FITTING screwdriver. Make sure the screwdriver is a snug fit in the slot before you strip out the soft brass with a screwdriver that is inferior. I use a hex type screwdriver bit. They are usually a hollow ground, reasonable quality, and come in graduated sizes.



The other tube is probably pressed in and if it doesn't have a slotted end, you may just want to put a drop of CLR in the tube and let it set for a few seconds before you rinse it out. This tube can be removed with a judicious use of a Easy Out, but much more trouble can be gotten into if you break the Easy Out. These tubes help atomize the fuel. They are a inch or so long and have cross drilled holes in their sides and a hole in the end.



Use the links Shep referenced to get a idea of what is involved. There is a guy on the forum (LRCXed) who will strip, clean, polish, and adjust your carbs better than new. Numerous members have used his services or purchased the book he wrote on carb service. I have yet to hear a negative comment on his work, and some have used his name in conjunction with a carb deity. The cleaning isn't hard, just exacting. The average member would probably spend 6-8 hours on the cleaning process alone to do a correct job.



Keep at it, and let us know your progress. Don't be shy about asking questions.
 

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Discussion Starter · #11 ·
I spent the past week collecting all the things I needed to follow Larry's detailed carburetor cleaning procedure, and finally finished this morning. I did everything except for extracting the idle jets. I didn't have the courage to risk breaking off the extractor tip, as I don't have spare sets of carburetors.



Here's what I found:



* One idle jet seemed plugged but I was able to route the #77 drill bit thru after a few probings.

* The other idle jet had some crud but was pretty easy to route out.

* The other circuits had a teeny bit of crud. Not much, really.

* The needle seats were pretty bad. It took five or six rounds of Q-tip+Brasso brass polish to get them clean.

* The float levels were WAY off. Roughly 2.3-2.5cm apiece. They're now sitting happily at 1.55cm, or, 15.5mm.

* I changed out a non-adjustable float (orange) for the original (black) after Larry informed me that they are not hollow inside and don't leak internally. (I had replaced it because it had a pinhole.)

* After assembly, it was hard to start again (!!!) Pulled the choke, fired only on one cylinder at first, then weakly on both, and eventually started warming up.

* However, after warm-up, I took it for a road test. The machine was VERY responsive off idle, but didn't have much power at the top end.

* After that, I checked the carb sync, and the sync was WAY off. I put them to equal and road tested again.

* After correct synching, the top end seemed to have a little more power, BUT - the low end had a touch of hesitation creep back in. ARRGH!



I should mention that "a touch of hesitation" is still much better than it was.



For the moment I am going to chalk the hard start up to the bowls still filling, perhaps, or maybe because the sync was so far off at first. I'll know for sure later tonight when it's had a few hours to cool back down.



FWIW, I can't find 1/4" brass rods anywhere in Utah! I want to replace those plug cap resistors, but I'll just have to keep looking for the brass. Is there some other substitute that works?



Thanks everyone!
 

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Are you certain you have the higher number jet in the brass hex fitting? If not, getting over 55 mph will be difficult.
 

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Discussion Starter · #14 ·
Are you certain you have the higher number jet in the brass hex fitting? If not, getting over 55 mph will be difficult.


Yes, thank you for the reminder, I think I'm good there. This bike does 85 if I ask it to, though I rarely drive it over 60.



Well I went to take it for a spin this morning. Not only did it start right up on the first crank, I almost didn't need the choke at all. After about 15-20 seconds of warm-up I had the choke completely off.



Then I took it up in the hills around my house and climbed about 1000 feet (plenty of power) up to a beautiful morning view of the Uintah valley, then picked some curvy roads back down to the house. The only problem was a little backfiring in the exhaust when engine braking, but this is no surprise as both pipes need new gaskets anyway.



Bottom line - I think I'm in good shape now thanks to all the help and advice on here! I'm going to take my wife on the Trapper's Loop ride out here near Ogden (UT) - it's been years since this bike's seen a good long ride.



Hope you are all having a great weekend!



Cheers,

-Jim
 

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Yes, thank you for the reminder, I think I'm good there. This bike does 85 if I ask it to, though I rarely drive it over 60.



Well I went to take it for a spin this morning. Not only did it start right up on the first crank, I almost didn't need the choke at all. After about 15-20 seconds of warm-up I had the choke completely off.



Then I took it up in the hills around my house and climbed about 1000 feet (plenty of power) up to a beautiful morning view of the Uintah valley, then picked some curvy roads back down to the house. The only problem was a little backfiring in the exhaust when engine braking, but this is no surprise as both pipes need new gaskets anyway.



Bottom line - I think I'm in good shape now thanks to all the help and advice on here! I'm going to take my wife on the Trapper's Loop ride out here near Ogden (UT) - it's been years since this bike's seen a good long ride.



Hope you are all having a great weekend!



Cheers,

-Jim
sweet
 
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