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1981 honda GL500
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Discussion Starter · #1 ·
Hey all, I recently bought a 1981 honda gl500 and everything was running fine, til about 2 weeks ago I noticed the right cylinder wasn't firing properly. I'm not too familiar with carburetors outside of they mix fuel and air, so I didn't want to attempt youtube tutorial dismantling and cleaning. I instead bought some carb cleaner spray and fuel additives to get it firing perfectly again. About three days ago I noticed the same issue, bogging down in first and second then jumping when throttling up in higher gears. I did the same technique I used before but it still isn't working. Do I need to just dive into a carb tear down? It seems like the float might be stuck so I thought blowing some carb cleaner into the main feed and letting it set for a bit would do it like before but, no dice. I dont want to damage anything as she's my only means of conveyance. Any help would be appreciated!
 

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81 Gl500i 83 CX650E
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How's the gas tank? Rusty tanks have a habit of plugging the idle circuit and sticking the right float shut .
 

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1981 honda GL500
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Discussion Starter · #3 ·
How's the gas tank? Rusty tanks have a habit of plugging the idle circuit and sticking the right float shut .

I looked and can't see any rust, I bought it from a guy and he said it would need some carb work and I figured I could handle it. But yeah the tank looks good from what I can see. I dont have an endoscope to do a deep look
 

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If you have any dought clean the tank and put fresh gas in it. That includes the screen on the petcock. Also open the drain screws and flush out the float bowls with carb cleaner or brake cleaner by spraying into the fuel inlet pipe. If it still runs the pits buy Larry Cargills book on rebuilding these carbs. Do you have compressed air available?
 

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They are a rather simple carb to clean , except the emusion tubes can be a difficult too get out of the carb body.
 

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1981 honda GL500
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Discussion Starter · #6 ·
If you have any dought clean the tank and put fresh gas in it. That includes the screen on the petcock. Also open the drain screws and flush out the float bowls with carb cleaner or brake cleaner by spraying into the fuel inlet pipe. If it still runs the pits buy Larry Cargills book on rebuilding these carbs. Do you have compressed air available?
I've done the first part, I only put in ethanol free gas, I sprayed carb cleaner in the inlet of the carbs and that fixed it the first time. I tried it this time, draining the bowls and even letting the cleaner sit in the bowls for a bit before firing and reattaching the fuel line, it blew out a bit of black smoke from the right exhaust, but still quit when I let off the throttle.
 

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If it's not firing at idle, but does when you rev it up, a blocked idle jet is a likely reason.
 

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One thing to check, are the idle screws still in the carbs ,aftermarket screws have a nasty habit of falling out and or wondering out of a adjustment, my 500 ran nice at 2 and a half turns out..
 

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1981 honda GL500
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Discussion Starter · #9 ·
One thing to check, are the idle screws still in the carbs ,aftermarket screws have a nasty habit of falling out and or wondering out of a adjustment, my 500 ran nice at 2 and a half turns out..
I imagine those are inside the carb?
 

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D-fresh is right download those manuals. The idle screws are on the bottom of the carbs in the middle just before the tube that feed the cylinders
 

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1981 honda GL500
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Discussion Starter · #12 ·
D-fresh is right download those manuals. The idle screws are on the bottom of the carbs in the middle just before the tube that feed the cylinders
The center is the idle adjust, are you referring to the small screws on either side?
207722
 

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'84 CX650E that is evolving into a GL500
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On bikes made for the US market those screws came with limiting caps glued on (so that owners couldn't adjust them enough to affect emissions) and the originals have ribs on the heads (inside those caps) so those are definitely not the original idle mixture screws.

BTW: 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 the Previous Owners may or may not have done 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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Hi Rich , sorry went for ride, yeah those are the idle screws and they look about the same amount screwed out. So yeah I think a carb cleaning is in order.
 

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I've recently been through a similar situation, i.e. not firing at idle, but does at higher revs. Thread here ... Is it dangerous to run on one cylinder?

In my case, the cause was vacuum leak (too much air) rather than blocked idle passages (not enough gas). For me the likely causes for the vacuum leak were torn diaphragm in the air cut off valve, tarn gasket on the intake manifold, and exterior crack in the rubber of the intake manifold. The first two causes seem more likely than the third.

In reading your thread, I would double check the diaphragm of the air cutoff valve. They are rubber and can be sensitive to carb cleaners. It's possible your cleaning caused the vacuum leak. Personally I avoid carb cleaner until all the rubber bits are out.
 

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I tend to have this issue every other season. I run murrays carbs on my 81gl500. I’ve found a new set of spark plugs does the trick. Don’t know why. I have the brass rod mods. All new stator and you name it. New plugs seems to do it for me. Good luck.
 

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I also had one cylinder dropping out at low revs. Turned out to be a spark plug tube. One was sparking across to head.
 

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I tend to have this issue every other season. I run murrays carbs on my 81gl500. I’ve found a new set of spark plugs does the trick. Don’t know why. I have the brass rod mods. All new stator and you name it. New plugs seems to do it for me. Good luck.
This, Especially if you recently got the bike and don't know how fresh the plugs are. They are under $5 each (at Canadian Tire here) and IMO should be among the first things you do to when you have rough idle and cylinders cutting in and out.
 
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