Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Technical Help Forum
Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Flash
07-19-2008, 4:43 PM
I wanted to go out for a ride today and notice gas leaking from my carb (left side). I shut off the fuel valve, and checked my service manuals (Clymer and Honda Official Shop Manual). It looks from the diagrams that there is a rubber o-ring and a rubber diaphram beneath the cover of the accelerator pump accelerator. I don't know a lot about motorcycle maintenance, but I know that the leaking gas is real fire hazzard and I shouldn't drive the bike. I need your advice on what to do. I assume I need to order a new o-ring and diaphram because they are old and probably cracked (allowing the gas to leak out). Am I right? Is this a big job? I read the manual and it looks like I need to take out the entire carbs to get to the cover and diaphram. Has anyone done this? Can you please help me, and let me know if this is a job for a professional or can I do it myself. Thank you. -Craig (Massachusetts)
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Blue fox
07-19-2008, 6:16 PM
Not a big deal to pull the carbs. First time maybe takes 30 minutes, faster the following times. I assume the GL engine is similar to the 79 CX that I have. Are you sure that the leak is from the accelerator pump? Mine doesn't have one, but my 750 does and they use similar carbs. In order, this is what you do:
1. Remove seat and tank
2. Loosen the top engine mount bracket behind the coils and pivot the bracket up and out of your way.
3 Remove choke cable bracket screw.
4. Loosen the 8mm nuts on the intake manifold, and loosen all the clamps on the airbox and intake boots.
5 Pivot the intake manifolds and you should be able to remove them from the carbs. Maybe a little leverage between the carb body and end of the boot with a screwdriver will help. Be gentle.
6. Once the intakes are loose, the airbox boots slip right out. Work from the left side of the bike to wiggle the carbs out toward you. I think there may be a vent hose to remove too that runs
between the carb bodies.
7. After you get the carbs partialy out, loosen the lower lock nuts on the throttle cables. I would mark which cable goes where too.
8. Slip the throttle cables and choke cable out of their holders and make sure the drain hoses are off, wiggle the carbs the rest of the way out. They acutually come out with plenty of room compared
to some other bikes.
I wouldn't order any parts until I knew what was bad, they want wayyyyy to much for accellerator diaphrams and cutoff valves. O rings can usually be sourced locally.
Blue Fox
79-CX500C, 82-GL500I, 82-GL1100, 76-CB550, 81-CB750C, 73-CB350F, 71-CT90
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Anonymous
07-19-2008, 6:53 PM
It sounds like I have a similar problem. One of my carbs is dripping from the bottom of the bowl. Someone suggested the float was stuck and instructed me to tap with a mallet. Trick didn't work - if he's right about the float, how should I take care of it? Note - I'm no mechanic, but I do get lucky most of the time! Josh
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Blue fox
07-19-2008, 7:07 PM
Is it dripping from the overflow pipe, or from the gasket at the top of the bowl? Overflow leaking is either float valve not seating properly, or crack in overflow tube inside of bowl. Tapping sometimes jiggles the valve into the closed position if there was just a bit of grit in the valve. Another thing to try is to shut off the petcock and run or drain the float bowls dry. This lets the float down completely and new gas may wash the grit into the bowl. If neither one of these work, take the bowl off and check the float valve for imperfections. It has been said that Brasso on a Q tip will polish the float valve cylinder and remove what may be causing it not to seal. I have also used 0000 steel wool on the end of a Q tip to do the same thing. If you have left the carbs on the bike, you can gently raise the float to close the valve and see if gas is still dripping. If the valve works, you either have it set at too high of gas level in the carbs, or you overflow tube is cracked. Fixing a cracked tube is easy by cleaning the tube with 400 sandpaper and melting a little solder over the crack. You should be able to spot the split, but they can be very tiny.
Blue Fox
79-CX500C, 82-GL500I, 82-GL1100, 76-CB550, 81-CB750C, 73-CB350F, 71-CT90
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Flash
07-19-2008, 7:55 PM
Thanks for the info. Blue Fox. When I pull the carbs out will they be full of gas? If so, can I just dump it into a bucket or will it go all over the driveway? I assume if I shut the fuel valve it will stop any fuel from entering the carbs. Is that true?
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Blindstitch2002
07-19-2008, 8:15 PM
Shut the petcock off. Place a can under the carb drain hoses and open up the screw on the bottom left side of the carbs and the fuel will drain out. Turn the screws back in. Disconnect the drain hoses and remove the carbs.
1978 Honda Cx500 Maggot
1979 Honda Cx500 Custom
1980 Honda Cx500 Deluxe Couch Project Bike
CX500 Factory Service Manual
Courtesy of Randall-in-Mpls
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Flash
07-20-2008, 3:38 PM
Thanks Blindstitch2002! I hope to tackle this job next weekend because I have to order the parts. Have you replaced the rubber diaphram in your carbs yet? Is it easy to get the diaphram out once I disconnect the carbs from the motorcycle? Thank you!
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Blindstitch2002
07-20-2008, 3:55 PM
Flash
It's really easy.
1978 Honda Cx500 Maggot
1979 Honda Cx500 Custom
1980 Honda Cx500 Deluxe Couch Project Bike
CX500 Factory Service Manual
Courtesy of Randall-in-Mpls
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
jkhinch25
07-20-2008, 7:08 PM
I'm tagging along on this thread, I'm the anonymous with the similar problem. Thanks to both for the detail. Looks like a piece of cake; wish I could've gotten to it today. Josh
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Blue fox
07-20-2008, 7:43 PM
If you guys do need a new accelerator pump diaphram, do a bench test to make sure it does squirt gas into the venturi. I had one with a good diaphram, but the orfices were gummed up and it wouldn't punch the gas thru. I also bypassed the air cutoff diaphrams with a rubber plug. (They were shot) Most threads on this indicate that they are unecessary if you richen the mixture a little. Their purpose is to prevent backfiring on deacceleration by enriching the mixture when the throttle is closed at speed. Our EPA deemed that mixture should be lean to save the polar bears, so Honda came up with this fix. I wonder how many of our 30 year old bikes still have the unadjustable mixture screws now? Check those diaphrams, I have not found many that are actually bad. Hold them up to the light, and if you see pinholes, replace, if not they may still be very usable. A lot depends on if they have been soaked with carb cleaner too many times.
Blue Fox
79-CX500C, 82-GL500I, 82-GL1100, 76-CB550, 81-CB750C, 73-CB350F, 71-CT90
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Blindstitch2002
07-20-2008, 8:00 PM
I can tell you I had one that I could see through and I blocked off the passage with a rubber but it kept eating at me to replace it. So I did. Didn't notice much difference with or without it.
1978 Honda Cx500 Maggot
1979 Honda Cx500 Custom
1980 Honda Cx500 Deluxe Couch Project Bike
CX500 Factory Service Manual
Courtesy of Randall-in-Mpls
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Flash
07-21-2008, 7:17 PM
Thanks for all the support. I ordered the entire rubber set from ebay yesterday for $25. There's still another brand new set if anyone needs it. The leaking gas is the main reason I'm concerned (leaking around the cover of accelerator). The bike was running well as of last week when I did a 100 mile trip. I don't need to adjust the carbs after I replace the rubber do I?
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Blue fox
07-22-2008, 6:15 AM
You shouldn't have to re-sync if you are just changing the diaphrams and O rings. You probably do want to adjust the idle mixture screws after renewing their O rings. I believe initial setting is about 2-1/2 turns out from LIGHT seating. That inner air cutoff diaphram cover can be removed using a small Vise Grip on the edges of the screws to get them started, then you can use a regular screwdriver to take them out from there. Leave the carbs attached to each other, and don't mess with the sync adjustment screw and locknut. Are you renewing both carbs, or just the one that is leaking?
Blue Fox
79-CX500C, 82-GL500I, 82-GL1100, 76-CB550, 81-CB750C, 73-CB350F, 71-CT90
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Flash
07-22-2008, 2:49 PM
Thanks for the info. I'm only doing the carb that is leaking (left side). I hope to get it out in one piece and leave them together. I don't want to adjust the carbs (re-sync) either. I'll keep you posted with the results... or more problems. :P
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Flash
08-01-2008, 2:04 PM
More problems... I replaced the diaphram kit, cleaned the carbs with carb spray, and put everything back together. No leaks, I went for a 60 mile trip and it ran well (more power than ever). The next day, I wanted to go for a ride, and smelled gas. I looked down and saw gas dripping from the bottom of the carb, worse than before. I don't know what is going on- it's driving me nuts. Do I need to replace the gaskets on the float bowls? The carbs are really clean after I cleaned them. Could the needle be stuck? I hit it gently with a wrench as the old wive's tale goes- - no help. Please let me know what could be going on with my left carb. I tightened the vent shut off when I drained the bowls, could that be it? What is the screw with the twisted wire on it? Thanks.
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Blindstitch2002
08-01-2008, 2:39 PM
There could be a blockage behind the needle valve or it might not be seating correctly. You only need to replace the float bowl gaskets if they are leaking where the float bowl connects to the bottom of the carb. You could try draining the carb that is leaking all the way and when it is finally empty open up the petcock and tap on it several times while it is filling up.
If it still leaks take that carb bottom off and examine the drain tube inside the carb for a thin crack. If theirs a crack solder it back together.
1978 Honda Cx500 Maggot
1979 Honda Cx500 Custom
1980 Honda Cx500 Deluxe Couch Project Bike
CX500 Factory Service Manual
Courtesy of Randall-in-Mpls
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Flash
08-01-2008, 3:14 PM
Thanks for your sage advice. I will drain it tomorrow, gently tap it while it is filling up... and pray! I'll keep you posted.
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Shep
08-01-2008, 3:21 PM
If you do have to take the carbs off and clean the Float needle hole and it's small valves a tip for when you have them off.Replace the inner most hard to access float bowl screw with an Allen screw.This makes it's much easier to remove the float bowls with the carbs on if some crud/grit gets into them and causes this problem.This is why I've also fitted cheap in-line fuel filters to try and prevent these problems.
HTH :)
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Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Flash
08-01-2008, 3:28 PM
Thanks for the suggestion. The carbs are a pain to get out and that would help a great deal if I need to get to float bowls.
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Shep
08-01-2008, 3:52 PM
These 2 things are most likely why I've not had any real trouble with my carbs once I serviced them nearly four years ago.I can drop the floats bowls in no time and check how well the in-line filter has done it's job and if I have to spray up the needle valve with some Brake/Carb cleaner and clean the bowls out :)
Note:I've also used an Angle grinder(Vice/Safety glasses and gloves) to take of some metal on the Carb bracket to allow easier access,
http://www.geocities.com/sheppola/carb/carb.jpg
on both sides so it's easier for me to set idle mixture as well as access idle speed knob :)
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Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Flash
08-04-2008, 4:12 PM
I sold the bike today to a college student who was tickled pink to get a bike to commute to school and his job. I was excited for him, as I remembered the day I bought the bike as a new rider three years ago. Moving on up to a ST1100 in the future.
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
RichNCT
08-04-2008, 8:02 PM
The ST1100 is a beautiful piece of machinery. It's been said it is the fully evolved CX/GL
Born to be relatively wild
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Shep
08-05-2008, 7:41 AM
Just think how awesome the ST1100s and Goldwings would have looked if they had kept them as a V4 engine mounted like the CX/GLs
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Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
RichNCT
08-05-2008, 9:34 AM
I thought they were the same "so called" transverse engine mounting as the CX/GLs?
Born to be relatively wild
Re: Leaking Gas from Carburetor 1980 CX500 with GL500 engine
Shep
08-05-2008, 12:47 PM
RichNCT wrote:
I thought they were the same "so called" transverse engine mounting as the CX/GLs?
Sorry yes the STs are.I was thinking of the old Goldwings flat fours.Funny enough I was chatting to a guy on an 1800 Pan european the other week but of course with all the fairing on you can't see the engine :(
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