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1979 Honda CX500C
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Discussion Starter · #1 ·
When I got home yesterday evening the moment I hit the kill switch my bike backfired. Since it was dark out I decided to investigate in the morning. Upon investigation I noticed fuel hanging in a droplet from one of the carburetors (I was facing the front/handlebar side). Specifically the right side carburetor when you’re facing the front of the motorcycle.

I’m going to provide photos of both carbs. Other than the backfire and this newly discovered leak the bike runs perfectly as far as I can tell but I’m also going to shoot a video of it idling and post it to see if any of you hear stuff that I missed.

Is that drip most likely the reason for the backfire and if so is it better that I get a rebuild kit and go ahead and replace all the gaskets etc on the carbs? Do you have any recommendations on rebuild kits? I’ve seen some on Amazon and eBay but I’m a little apprehensive about shopping at either for something as important as the carburetors.
 

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Discussion Starter · #2 ·
When I got home yesterday evening the moment I hit the kill switch my bike backfired. Since it was dark out I decided to investigate in the morning. Upon investigation I noticed fuel hanging in a droplet from one of the carburetors (I was facing the front/handlebar side). Specifically the right side carburetor when you’re facing the front of the motorcycle.

I’m going to provide photos of both carbs. Other than the backfire and this newly discovered leak the bike runs perfectly as far as I can tell but I’m also going to shoot a video of it idling and post it to see if any of you hear stuff that I missed.

Is that drip most likely the reason for the backfire and if so is it better that I get a rebuild kit and go ahead and replace all the gaskets etc on the carbs? Do you have any recommendations on rebuild kits? I’ve seen some on Amazon and eBay but I’m a little apprehensive about shopping at either for something as important as the carburetors.
When I got home yesterday evening the moment I hit the kill switch my bike backfired. Since it was dark out I decided to investigate in the morning. Upon investigation I noticed fuel hanging in a droplet from one of the carburetors (I was facing the front/handlebar side). Specifically the right side carburetor when you’re facing the front of the motorcycle.

I’m going to provide photos of both carbs. Other than the backfire and this newly discovered leak the bike runs perfectly as far as I can tell but I’m also going to shoot a video of it idling and post it to see if any of you hear stuff that I missed.

Is that drip most likely the reason for the backfire and if so is it better that I get a rebuild kit and go ahead and replace all the gaskets etc on the carbs? Do you have any recommendations on rebuild kits? I’ve seen some on Amazon and eBay but I’m a little apprehensive about shopping at either for something as important as the carburetors.
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Did it backfire through the carbs or afterburn in the exhaust system? If it was an explosion in the exhaust system that could be due to an air leak mixing with un-burnt fuel.

Hard to tell where that fuel came from. Were you able to identify a specific leak? Do more diagnostics before spending money on kits.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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It looks, to me, like you need proper bowl gaskets, rather than the plumber's putty that's in there now.
 

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Discussion Starter · #5 ·
So I checked it out further and there’s no more leaking from that spot and no cracks or anything suspicious, I turned it on a let it run for around ten minutes seeing if getting it hot would cause it to leak again and nothing. I did just fill up the gas tank, maybe I just spilled a little gas and hadn’t noticed? Also, no backfire when I hit the kill switch this time.

Something I hadn’t thought about that is probably important information or at least a little useful. I was nearly out of gas a couple weeks ago and filled up with regular unleaded from a nearby shell. This time I filled it with the ethanol free stuff from a nearby racetrack gas station. Could that have caused the backfire?

Also, in regards to the gasket. Do I get replacements with the rebuild kit or should I order them separately?
 

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Discussion Starter · #6 ·
Did it backfire through the carbs or afterburn in the exhaust system? If it was an explosion in the exhaust system that could be due to an air leak mixing with un-burnt fuel.

Hard to tell where that fuel came from. Were you able to identify a specific leak? Do more diagnostics before spending money on kits.
Dumb question maybe but how do I know where the backfire came from? Would a specific sound point to a specific location?
 

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Discussion Starter · #7 ·
Dumb question maybe but how do I know where the backfire came from? Would a specific sound point to a specific location?
It essentially made a pop sound followed by what sounds to me like a sort of puff of air.
 

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Possibly you flicked the kill switch off-on-off quickly without realizing it. Under some random circumstances of that can cause a pop from the exhaust. The float bowl “gasket” is a formed o-ring and they are very long lasting, I have never replaced one unless I damaged it. As Randall noticed, it appears there may be some other sealant in that joint too. It would make me curious.
 
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Discussion Starter · #9 ·
Possibly you flicked the kill switch off-on-off quickly without realizing it. Under some random circumstances of that can cause a pop from the exhaust. The float bowl “gasket” is a formed o-ring and they are very long lasting, I have never replaced one unless I damaged it. As Randall noticed, it appears there may be some other sealant in that joint too. It would make me curious.
Interesting. I work tonight so I’ll definitely be listening for anything and will update tomorrow. I’ve opened both float bowls when cleaning and then syncing the carbs and nothing seemed broken (I imagine it would be obvious if the o rings were broken) but it probably wouldn’t hurt to check again right? I’m going to look again but I think what appears to be sealant is just dirt.
 

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Discussion Starter · #10 ·
Possibly you flicked the kill switch off-on-off quickly without realizing it. Under some random circumstances of that can cause a pop from the exhaust. The float bowl “gasket” is a formed o-ring and they are very long lasting, I have never replaced one unless I damaged it. As Randall noticed, it appears there may be some other sealant in that joint too. It would make me curious.
I just looked, not dirt. Definitely some weird sealant or something. Not sure how I missed this.
 

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The bowl o-ring will develop a flat side that sometimes leads to a failure. A PO might have been trying (poorly) to correct that.
The bowl gaskets are pretty cheap on eBay.
 

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'84 CX650E that is evolving into a GL500
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Silly question: Why did you use the kill switch to shut it off instead of the keyswitch?
The kill switch is there for the rare occasions you find yourself in a situation where you need to stop the engine but you can't take a hand off of the handlebar to reach the key. In over 36 years on bikes and year round for most of that I can only remember having to use it on 2 occasions. Once was when the throttle cable froze and I had to use the kill switch to pulse the engine to get the bike stopped under a light where I could try to deal with it and the other time when the palm of a mitt I was wearing was trapped between the clutch lever and the grip, preventing the clutch from disengaging enough to kick it into neutral while stopped at a red light on a hill so I couldn't let go of the brake either (I replaced those mitts ASAP).
 

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I always shut down with the kill switch. It's right there by my thumb.
Regular cycling also keeps it functional by wearing off any corrosion.
 
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Discussion Starter · #14 ·
Silly question: Why did you use the kill switch to shut it off instead of the keyswitch?
The kill switch is there for the rare occasions you find yourself in a situation where you need to stop the engine but you can't take a hand off of the handlebar to reach the key. In over 36 years on bikes and year round for most of that I can only remember having to use it on 2 occasions. Once was when the throttle cable froze and I had to use the kill switch to pulse the engine to get the bike stopped under a light where I could try to deal with it and the other time when the palm of a mitt I was wearing was trapped between the clutch lever and the grip, preventing the clutch from disengaging enough to kick it into neutral while stopped at a red light on a hill so I couldn't let go of the brake either (I replaced those mitts ASAP).
I use either. Usually the key then kill switch, sometimes the kill switch then the key. I’ve taken the MSF course a few times and the instructors use either so I just assumed it didn’t matter which you used. I’ll start using the key switch first though if that makes a difference.
 

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It doesn't matter. Some people just seem to think it makes them smart not to touch the kill switch.
 
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The kill switch just kills the ignition. The keyswitch turns everything off. You are going to have to turn the keyswitch off no matter what so why bother with the kill switch?
The most common reason I use the kill switch is if I'm working on something electrical and turn everything I can off so I don't drain the battery.
 

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It doesn't matter. Some people just seem to think it makes them smart not to touch the kill switch.
I don't use the kill. no particular reason.

Some instructors though do tell you to shut down via the kill switch to form the muscle memory habit of using it ready for the day you need it.

Meh.
 
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