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1980 Honda CX500C
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Discussion Starter · #1 ·
I recently purchased my first motorcycle, a 1980 Honda cx500c that had been sitting for two years. Now I've never really worked on anything mechanical until now but I changed the oil, cleaned air filter, took carb out and apart and replaced gaskets and float needles and cleaned jets and bike would start fine but was pouring gas from right carb still. Took it apart again and this time replace o rings on fuel transfer pipe and air cut off valves while I was at it as well as replace drain screw o rings and once I switched petcock from off to on it wasn't leaking anymore, then I started it up and it started leaking fairly heavily from around gasket (which I had just replaced), I think I may have not seated it properly and cinched if the first time. Uncle rides harley and is president of a club and suggested I dab rtv on gasket and try to get as clean as possible then reattached bowl. Now I'm waiting for 24 hours for it to cure before I turn the petcock back on. I used high temp red rtv. If this doesn't work, what are my options? Can I find a cheap RH carb replacement somewhere? Or should I just say screw it and take the carbs to a shop to be redone completely? Also, if some terminology is wrong, please keep in mind I literally just learned all of this by watching videos and looking up diagrams lol
 

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The fuel level in the float bowl should be a couple of millimeters below the joint with the body. A heavy leak there suggests that the float needle valve is not sealing properly. Did you keep the parts that you replaced? If so try putting the original float and needle valve back in. I'd suggest doing the same with the bowl gasket if you still have the original.
 

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Discussion Starter · #3 ·
I do have both float valves, but only one gasket, the other was torn and being held together by the other person who previously used rtv. But shouldn't a new gasket be better than the used one? Or did I ruin its integrity by cinching it the first time?
 

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'84 CX650E that is evolving into a GL500
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It is pretty common for any jets, needles &c that come in aftermarket carb kits to be so far out of spec that they cause more problems than they could ever fix (not to mention reports of peeling plating on aftermarket float needles). Add to that how rare it is for the original parts to wear out or otherwise need to be replaced and you can understand why we always recommend keeping the original ones and tossing the aftermarket crap.

The term "RTV" (= Room Temperature Vulcanizing) is commonly used by people who don't understand the term to refer to silicone sealant but it really means ANY rubberlike compound that cures without heat so it is best to say "silicone sealant" when that is what you mean.
All good intentions from your uncle aside, using silicone sealant on any part of the fuel system is not a good idea because gasoline will attack the silicone. You would be far better off to make sure the gaskets are seated properly and tighten the screws to the specified torque.

Welcome to the forum. Please add your location and your bike's model and model year to your profile so that you don't have to remember to tell us every time and we don't have to keep asking when you forget (see Forum Settings link in my signature).

And welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old and may or may not have had all of the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. Check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for modern stainless braided ones (they last practically forever and double the life of the fluid). And don't forget things like the rad hoses and the boot between the engine and swingarm (they can crack on the bottom where you don't see it).
 

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Discussion Starter · #6 ·
Update:
Good news is that the carb is no longer leaking. Bad news is she doesn't want to stay running so I'm fairly certain I clogged the jets with the rtv. If I remove this bowl and let the jets soak in carb cleaner and thoroughly clean the edges of any rtv residue will that solve the issue?
 

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Update:
Good news is that the carb is no longer leaking. Bad news is she doesn't want to stay running so I'm fairly certain I clogged the jets with the rtv. If I remove this bowl and let the jets soak in carb cleaner and thoroughly clean the edges of any rtv residue will that solve the issue?
You should buy Larry’s carb book and do the job right. I have and while I’ve done many carbs before I still learned a few more things specific to those carburetors. Good investment. CX500/Gl500 Carb book

Dan
 

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Discussion Starter · #8 ·
Is it possible it could be the fuel filter? Haven't been able to locate it. I'm sure I sound about as green as can be... lol. But thank you danroy, I've been looking for a service manual
 

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Is it possible it could be the fuel filter? Haven't been able to locate it. I'm sure I sound about as green as can be... lol. But thank you danroy, I've been looking for a service manual
The factory service manual may be downloaded from the wiki, link in my signature. The only fuel filter in a stock system is inside the fuel tank. To get at it you have to remove the petcock.
 

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Discussion Starter · #11 ·
I was pretty meticulous about only using small dabs on the gasket, just enough to get it to seat properly. The only reason I'm thinking that is because it ran fine before I put the rtv on, aside from the leaking carb of course, and now I can drain the carb and then start her up again and she'll run for a solid 2 minutes and then bog out
 

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I was pretty meticulous about only using small dabs on the gasket, just enough to get it to seat properly. The only reason I'm thinking that is because it ran fine before I put the rtv on, aside from the leaking carb of course, and now I can drain the carb and then start her up again and she'll run for a solid 2 minutes and then bog out
It runs better after you drain the carbs? Looks like your new float valves don’t seal properly and flood the carbs. OEM ones are long lasting and seldom require replacing. Aftermarket ones often aren’t good sealing I’ve heard.

Add an in-line fuel filter between the petcock and the carb inlet. It’s good prevention with our old and sometimes rusty fuel tanks.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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I was pretty meticulous about only using small dabs on the gasket, just enough to get it to seat properly. The only reason I'm thinking that is because it ran fine before I put the rtv on, aside from the leaking carb of course, and now I can drain the carb and then start her up again and she'll run for a solid 2 minutes and then bog out
Maybe it becomes too rich now that the excess fuel isn't escaping.
 

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Discussion Starter · #14 ·
So it could be an air intake issue? The boots are pretty old but I don't see or feel any cracks. Also had a local mechanic suggest bending the float rod to adjust the fuel in the carb and that should help the leak issue after I clean it out again
 

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'84 CX650E that is evolving into a GL500
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If he meant to bend the shaft that the float pivots on I would highly recommend avoiding him in the future.

Did you put the original float needles back? If not it is very likely that your incorrect float height is caused by out of spec aftermarket ones.

If you don't believe us READ THIS:
 

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Discussion Starter · #16 ·
Not as of yet, but I'm inclined to go with what you guys say before a random small engines guy, so I'm gonna take the carb back out tomorrow and replace the float valves and will get back to you. Thank you again guys
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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He may have meant bending the float frame to adjust the fuel level. If you attach a clear tube to the carb drain and bend it up next to the mounted bowl, you'll see where the fuel level is.
 
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Discussion Starter · #19 ·
Thank you guys for all the help, I've got her running and she sounds pretty good! Not quite as responsive on the throttle as I might like but from what I gather that's just a little tuning. Perfect week to have a bike!
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Hey, another Minnesotan, I see!
The 15th annual Spring Ride is Saturday, June 4th. It would be a long haul to the start in Pine Island, but you're welcome if you're up for it. Otherwise, consider riding down to the Barbecue, starting about 5:00.
 
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