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Discussion Starter · #1 ·
The left carb on my 80' cx500 is leaking fuel out of the drain line. Does anyone know if there's a good website to order a set of drain screw o-rings without purchasing a whole rebuild kit?

I've seen a pack of four on "cyclewareables.com" but the website seems a bit shady, and has received a lot of bad reviews from people who've ordered through them.
 

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Have you checked to see if the drain tube for the overflow is cracked? It's a very common problem with these carbs. The O-ring is only there to keep dust and water out of the drain screw threads.

Also, check the tip of the drain screw for rust pits on the tapered tip of it.



This is an extreme crack. Not all of them are this bad. Most times you'll just barely be able to see it.

 

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Discussion Starter · #3 ·
Thanks, I didn't think of that... I did try to test the drain tubes when I cleaned the carbs by dripping fuel down the tube, but even as I was doing it I knew that there were probably air pockets keeping the tube from filling with fuel. It was a pretty half-hearted attempt at testing them.

Do you have a method that works well? or do you just use a magnifying glass?
 

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The easiest way to check if the bowl drain tubes are cracked is to remove them and fill them with fuel. Water may work, but it has a higher surface tension than fuel, and may not flow through a crack as easily. Before filling the bowl, use a small wad of 0000 steel wool to clean the outside of the tube. This makes it much easier to detect a split. Also use the steel wool to burnish the drain screw seat and end of the drain screw itself.



If the overflow drain leaks when the screw is snuggly seated and fuel is up to slightly below the top of the bowl, you probably have a split tube. As Larry says, sometimes the split is not obvious, so examine closely. A split can be repaired easily by soldering the outside of the tube. Just have it clean and bright and use a micro torch to heat the tube to soldering temperature. Make sure that you use flux or flux cored solder too. When the heat is right, the solder will flow smoothly over the split and you have a permanent fix.



If the split continues to the bottom of the tube, you may have to use a dab of JB Weld there as solder will not adhere to the aluminum bowl.



This is one of the easiest repairs to do on these bikes. If you don't have a micro torch, I would recommend picking one up from Harbor Freight for about $6.00. They come in handy for heating stuck bolts and screws before using penetrating oil too.
 

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The best way I have found to find a cracked tube is by filling the bowl with water, drain screw tightened up of coarse, block the top of the tube with your finger tip and blow compressed air in through the bottom of the bowls drain. Any leak will show up that way.

I started doing it this way when I discovered that some of the tubes that were leaking didn't have a split in them, but were actually cracked around the base from being bent side to side in it's past. I've been cleaning tubes up with steel wool before only to have them come right off with hardly any pressure at all. Those are fun to repair because that piece has to come out before I can put a new tube in.
 

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Discussion Starter · #6 ·
Thanks guys, I'll check it out today... hopefully that's what the problem is.

After thinking about it... is there any chance it could be the float needle not seating properly? I used a Q-tip and toothpaste to clean the seats before I put the carbs back together. The rubber on the needles looked fine. (would that cause the bowl to fill up above the overflow tube?)
 

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Thanks guys, I'll check it out today... hopefully that's what the problem is.

After thinking about it... is there any chance it could be the float needle not seating properly? I used a Q-tip and toothpaste to clean the seats before I put the carbs back together. The rubber on the needles looked fine. (would that cause the bowl to fill up above the overflow tube?)
yes,Todd,without stepping on the experts toes,it would.you needle valves are your automatic cut off valves.if it does not shut off,you will forever supply fuel to the carb thats not calling for it.

connect a clear pipe to your drain,run it up along the carb body.it should show a finished level just a fraction below the seam.
 

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Discussion Starter · #10 ·
Well guess what.... I connected the clear tube, opened the petcock... and no leak. It must have been the float needle not seating properly. I didn't do anything to the carb... not even tapping it. weird... Oh well, guess I'll just keep an eye on it.

Thanks for steering me in the right direction guys, I really appreciate it. I would have spent time and money on unneeded o-rings.



Bye the way... this is the first time I've had the bike running for more than a few seconds at a time, since I got it. I pulled the carbs and cleaned them right after I got the bike because it had old gas that had been sitting in there for who knows how long. (major varnish). I ran into a few problems while cleaning the carbs... the worst one was the ez-out that snapped off in the slow jet while trying to get it out (alot of cussing finally caused the jet to just fall out in my hand
... well ok, some heat and tapping probably helped too.)



I just now had the bike running long enough to get it up to running temperature. YAY!! It sounds good too... it seems to be burning a little rich though so I guess i'll figure out how to adjust the mixtures.

Should I synch the carbs first?
 

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Did you have the mixture screws out when you did the carb cleaning? There should have been a tiny washer and an O ring in the seat area. Most times these don't fall out on their own (well, the O ring doesn't, but the washer may). Both are important to the operation of the idle circuit. And the O ring can get bad and block a circuit. If you haven't notched the "stop" tab on the float bowl, or clipped the wing off the needle valve, you won't be able to remove these with the bowls on.



The normal starting point for these is 2-1/2 turns out from lightly seated. That also assumes the internal idle circuit is clean and clear. But it is a good starting point. Out for richer, in for leaner idle operation. You basically adjust for highest idle speed, but this requires a portable tach or a really good ear. And keep the initial idle speed around 1100 RPM's when you start to adjust.



Syncing the carbs can be done after you get the idle mixture worked out. If you haven't messed with the sync screw, it shouldn't be too far out of sync.
 

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Don't neglect to install an inline fuel filter between the petcock and the carbs if you didn't already. The tiniest bit of tank rust can keep the float needle from seating properly.
 

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Discussion Starter · #13 ·
thanks guys,

I learned about the idle washers the hard way... I lost one of them when I was cleaning the carbs because I didn't realize they were in there until it was too late... I either threw the washer out with the cleaner, or I blew it into a far corner of the shop with the compressor. Luckily "instructorpilot" was kind enough to send me two washer and o-rings all the way from Florida.

My second mistake after finally getting the washers was to put one on an idle screw and then put the screw down into the hole and tighten it down to lightly seated.... unfortunately the washer had twisted in the hole so it bent when I "lightly" seated the screw.
After calling myself several choice words, I checked out the seat and idle screw with a magnifying glass to see if I had damaged them. Luckily I didn't see anything wrong, so I put the extra washer on the screw and tipped the carb body upside down so it would stay on the screw in the right position as I carefully seated it. I have them both at 2 turns out right now because that's what the factory service manual calls for (that's probably the problem).



When I adjust the mixture do I set the main carb first and then do the other one?



Thanks for the advice StormRider, I've already pulled the old filter out of the tank and installed an inline filter... the last thing I wanted was to go through all that and then have tank sediment clog everything up again.




I was literally crawling around my shop trying to find that tiny washer... and then went outside to the burn barrel and pulled each individual leaf out looking for the washer.. in pouring down rain. (I had dumped the used carb cleaner in my burn barrel). I finally gave up after going down about two feet through wet leaves.



lots o' fun...
 

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Thats good, have had too much experience with that bit of preventive work myself.

I remember unintentionally impressing some friends with how quickly I could pull the carbs and clean out the float bowls, needle and seat on my cm400.( I was so broke that I couldn't the 5$(USD) for a filter and had to mess with them far too often.

A couple months ago I pulled the carbs to fully disassemble and clean them out - and see how similar they were to the CX carbs. They were amazingly clean inside, looked better than the last time I had them all torn down a few years ago. Hooray for Seafoam! The CM400 carbs are very similar, just a bit smaller. Anyway.... When I reinstalled them the old hardened fuel line would not go back on the fuel filter. A five minute test run without the filter couldn't possibly hurt........



WRONG! flooding again.... The bike got to sit and wait for new fuel line after that.

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(there is no "Main" akaik on the 1980 version at least)



Initial pilot screw adjustment in the FSM '80 addendum is 1 3/4 turns out



Basic procedure I use -



0. Make initial setting if carbs have been apart.

1. Set idle speed.

2. Adjust one carb for highest idle gain - make sure to try both directions from initial setting

3. Reset idle speed if needed

4. Adjust other carb

5. Start back at 1. until happy with results (at least once)



Make sure that before carb:



Engine is operating temperature

cam chain and valves are adjusted



Just noticed Blue Fox's post above - the addendum's leaner initial setting may have been to reduce emissions and not for best performance.



Good Luck!
 
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