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Discussion Starter #1
I bought this bike as another project from a so-called bike shop That was closing down. Owner said that he had been through the carbs, but when I fitted to the bike, they were leaking like a sieve. I have since cleaned and rebuilt them, but I am struggling with one thing: there seems to be a flexible fuel line connecting the carbs, going from one nipple to the other, but it is obviously not the primary supply line (brass tube) and I cant see the same tube in any online photos. It almost looks like overflow ports and I am wondering if the prior owner had them connected together because it was gummed up and leaking so badly. I have attached a few photos and am looking for some feed back from the group, since the manual has
198919
198920
very little information on the Carbs. Appreciate any and all assistance.
 

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The brass tubes sticking out the side of the carb are vents/breathers to allow air at atmospheric pressure to enter the float chambers.
Some owners seem to think these need connecting to each other - they don`t.
Remove the tube and let your carbs breathe!

..it`s not the first time we`ve seen this.
 

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Discussion Starter #3
The brass tubes sticking out the side of the carb are vents/breathers to allow air at atmospheric pressure to enter the float chambers.
Some owners seem to think these need connecting to each other - they don`t.
Remove the tube and let your carbs breathe!

..it`s not the first time we`ve seen this.
Awesome! Really appreciate the help. Back in the bike they go!
 

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Discussion Starter #4
So carbs are back in the bike, it started up first turn (great sign) and will rev to around 2500 rpm then starts coughing when I open the throttle more. Strange thing is that when I cut the fuel supply off at the petcock, just before it dies, it revs to around 4000. Still a carb issue? I did notice that the prior owner had replaced the bras screws at the back of the float bowls (outside the bowl) but again, cant find any reference to these screws in the manual. Any ideas?
 

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Discussion Starter #5
So carbs are back in the bike after cleaning, it started up first turn (great sign), idles just fine and will rev to around 2000 rpm, then starts coughing when I open the throttle more. Strange thing is that when I cut the fuel supply off at the petcock, just before it dies, it revs to around 4000. Still a carb issue? I did notice that the prior owner had replaced the bras screws at the back of the float bowls (outside the bowl) but again, cant find any reference to these screws in the manual. Both cylinders are getting spark, but left side header is far cooler than right side. I gave it a first spin round the block and it looks like the left side is only intermittently contributing. Any ideas?
 

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Get a length of 4 mm clear hose and put it on the drain nipple under the float bowl.

With the petcock turned on open the drain screw in the float bowl. Fuel level will show in the tube and should be a couple of mm below the carb to floatbowl joint.
 

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By brass screws, do you mean the mixture screws at the FRONT of the float bowls?

Try screwing them in until they lightly bottom and then turn them back out by 2.5 turns as a baseline.

Also, when initially screwing them in take note of how many turns out they are now.

Check your float bowl fuel level. And your air filter.
 

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Discussion Starter #8
Get a length of 4 mm clear hose and put it on the drain nipple under the float bowl.

With the petcock turned on open the drain screw in the float bowl. Fuel level will show in the tube and should be a couple of mm below the carb to floatbowl joint.
Checked the voltage in the battery when running, 15v. Checked the fuel level in both Bowles with clear plastic hose and is just below the bowl seal, which looks correct. Just did a compression test on both sides and both measure 130 with throttle completely open. Right side header is very hot, left side only warm. Removed left side spark plug, which looks quite new and see some carbonization, but plug was dry. Check coils and both sides are getting spark. Sounds like it has to be starved of gas on left side, so is a carb issue. Agree? Now, any idea what the carb issue could be? Jets are clear, pistons and needles move freely..... am not a carb expert, but I cleaned out every orifice I could see.
 

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Discussion Starter #9
By brass screws, do you mean the mixture screws at the FRONT of the float bowls?

Try screwing them in until they lightly bottom and then turn them back out by 2.5 turns as a baseline.

Also, when initially screwing them in take note of how many turns out they are now.

Check your float bowl fuel level. And your air filter.
Set the screws as suggested. Checked the voltage in the battery when running, 15v. Checked the fuel level in both Bowles with clear plastic hose and is just below the bowl seal, which looks correct. Just did a compression test on both sides and both measure 130 with throttle completely open. Right side header is very hot, left side only warm. Removed left side spark plug, which looks quite new and see some carbonization, but plug was pretty dry. Check coils and both sides are getting spark. Sounds like it has to be starved of gas on left side, so is a carb issue. Agree? Now, any idea what the carb issue could be? Jets are clear, pistons and needles move freely..... am not a carb expert, but I cleaned out every orifice I could see.
 

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Have you balanced/synched the carbs yet? It could be simply the left carb's butterfly isn't opening as far as it needs to relative to the right so the right side is doing most of the work.

BTW: I merged the 2 threads you started about the carbs. Asking the same thing in multiple places makes it hard to follow the ensuing discussions.
 

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Discussion Starter #12
Have you balanced/synched the carbs yet? It could be simply the left carb's butterfly isn't opening as far as it needs to relative to the right so the right side is doing most of the work.

BTW: I merged the 2 threads you started about the carbs. Asking the same thing in multiple places makes it hard to follow the ensuing discussions.
Thanks Bob.
Started the carb rebuild this morning using “Larry’s Guide” and 2 things I have noticed, hoping I could ask questions on:

One of the fuel mixture screwed is broken at the needle, which is stuck inside the carb body. Any suggestions on how to remove, besides an ultrasonic soak?

One of the emulsion jets has a damaged head. I am soaking the carb body in ultrasonic bath now, I still have a little purchase on the head with filed-down screw driver, but if the ultrasonic doesn’t work in freeing it up, any suggestions?
 

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See page 48 of Larrys guide for the broken mixture screw
Are you talking about the low jet emulsion tube? I don't believe the 79 has the screwing in jet, but is actually pressed in. See pages 13-14
 

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Discussion Starter #14
See page 48 of Larrys guide for the broken mixture screw
Are you talking about the low jet emulsion tube? I don't believe the 79 has the screwing in jet, but is actually pressed in. See pages 13-14
Followed Larry’s guide and unfortunately ended up having to drill out one of the emulsion tubes. good news is that the threads are undamaged. Bad news is that I can’t seem to find a replacement emulsion tube (part #16166-415-003] anywhere. Have tried eBay as well as all the usual bike part sites and they are all out of stock. Am kind of wishing I had just left the damned thing in there and hoped for the best. Any ideas where I can get a replacement emulsion tube?
 

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Paul, check your email. I sent you one.
 

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Discussion Starter #16
Paul, check your email. I sent you one.
Thanks Larry, got your email and appreciate the assistance. Any idea where I can get the replacement emulsion tube?
 

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Discussion Starter #17
Well, after 2 weeks of cleaning, discovering more carb issues and a massive amount of help from Larry Cargill (thanks again sir’) my carbs running like a champ, but the engine is still choking at 4000rpm (turns out tachometer is bad, so the issue is 4000rpm). Idles beautifully, but at exactly 4000rpm, it starts spluttering. Does this sound like an issue with the CDI? Does it change behavior, or use a different map at 4000rpm?
 

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Well, after 2 weeks of cleaning, discovering more carb issues and a massive amount of help from Larry Cargill (thanks again sir’) my carbs running like a champ, but the engine is still choking at 4000rpm (turns out tachometer is bad, so the issue is 4000rpm). Idles beautifully, but at exactly 4000rpm, it starts spluttering. Does this sound like an issue with the CDI? Does it change behavior, or use a different map at 4000rpm?
The copper wires insulation has broken down on the secondary power windings.
It will never run over 4000rpm unless cdi unit is converted over to digital box.
New CDI UNIT will do nothing to solve problem.
All 500's will suffer this issue.
 

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Discussion Starter #20
The copper wires insulation has broken down on the secondary power windings.
It will never run over 4000rpm unless cdi unit is converted over to digital box.
New CDI UNIT will do nothing to solve problem.
All 500's will suffer this issue.
You may have nailed it. I just did the stator test (thanks to post from reclinedrelic) and I got the following results, which I guess means I either need to drop the engine (again) and change out the stator, or convert to digital? Is the digital conversion an easy one? Any pros or cons to doing the conversion versus replacing the stator? I am assuming that the stator will keep on charging as it is based upon escorts below
199304
 
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