Why is gas leaking from carbs?

OK, so I have had my XJ550 Maxim for a month now and I'd like to thank all the people on this site for being so descriptive and motivational. I have searched high and low for the answer to my question but have not been so lucky as to find an answer. Like I said, I got the bike a month ago from the original owner, the bike is in very good condition with only 3600 original miles. The PO obviously didn't ride very much and consequently had to have the carbs cleaned often by a mechanic friend of hers. She told me that she just had the carbs cleaned, float valve's and needles replaced, and float bowl gaskets replaced. After having the bike for a couple days, and it being very tempermental i.e. not wanting to start, I went out to my garage and was welcomes by a puddle of gas. Being that I am not a mechanic and at that time had no idea about how to work on the bike, I brought it in to a local shop. I originally thought I was leaking gas from the carbs. I also told the guy that there was also an intermittent idle at around 3000-4000 rpm's. After checking it out the guy said it was a leaking petcock, and that I probably had a vacuum leak, but he could not diagnose the vacuum leak until the petcock was fixed. Then he told me it would be $150 to replace the petcock. That $150 was my incentive to find this site. After looking through the various posts, and looking at my bike, i decided I would try to fix the problem. First I dismantled the Petcock and looked for the problem, which didn't help. After messing with it for a day replacing variopus parts the vacuum was still non-existent, so I ordered a new one. While waiting for that to arrive I pulled the carbs to clean them and inspect/compare the insides to my manual. All of the float bowl gaskets are in excellent condition, no tears rips creases or any such thing. The float valves and needles are definately new. The bowls were spotless as well. The one thing that I did notice is that one of the diaphragm's seems worn, I cannot locate any hole but it does have a crease and some fraying along the crease. The intake and manifold boots are all in really good condition, again no tears or cracks. After reassembling the carbs and recieving my new petcock, I put it all back on the bike. Set the petcock to prime, started the bike, and set it to on. At first she was running great, but then died. This is when I noticed fuel collecting on the plate under the carbs in between the #1 and #2, carbs. Since then I have checked the float levels, adjusted them who knows how many times, and no matter how high or low the float levels are it still leaks. She runs but idles either too fast or not at all. When I give it throttle it hangs around the 4k mark. I have replaced the plugs, and upon checking the new ones, they are grey in color. I also checked for a vacuum leak with WD-40, but that didn't seem to have any effect whatsoever. So today I'm gonna pull the carbs of again, and I am not putting them back on until I know I have fixed the problem. Ok, finally, my question.
#1 Is it possible that the gas is leaking from the to of the carbs due to a faulty diaphragm?
#2 What else should I be looking for?
#3 Where can I get some of the stainless steel allen head float bowl screws?(The links I have found in other posts have pictures but no way to buy)
Well I know this is long winded but I wanted to give you the best description I could. I hope I didn't forget anything.
8O

 

Your mechanic is right about the petcock however the price seems a little steep. You can get a replacement for about $50 online or if you choose to rebuild the little bugger it will cost a little over $20. I would go to http://www.partsnmore.com , they have a rebuild kit that comes with all the little rubber bits. Make sure if you go this route though, don't just pull it apart, throw the new pieces in and put it back together. Every surface in your petcock will need to be cleaned to ensure proper operation. I'm just guessing here but when you pull your petcock you will probably find a worn valve, it's a rubber circle with 5 holes in it. It is supposed to have have raised areas sealing one opening from the others but they tend to break down with time.

 

There should be no gas on top of the diaphram above the slide valves!!

To trouble shoot this you would start with the most logical thing that could be causing this problem.
1st you wouldnt have gas leaking with the engine off unless there was a problem with your petcock (left in prime or bad sealing parts like artistic_gore said)
The 1st thing you replace is the cheapest so I'd say that you should rebuild your petcock with a replacement parts kit, when done the petcock should let no fuel leak out in the on/run position or RES position but should let gas run when there is a vacuum on the vacuum line. Also gas should run in the prime position (only to fill your float bowls)

If this helps carbs to quit dripping gas, then ........ success!!

If not then the next thing to suspect is possibly bad float valves!?
but they shouldn't leak with the bike off, only when it's running and your engine should be flooding or running real rich.
(did you mention if the carbs were leaking when running or not?)

I wouldnt pull the carbs untill I was sure it wasn't the petcock, seems the most logical thing to me.
Good luck
Mike

 

Thanks for the info. I guess I should have been a little more specific about a few things. I have already replaced the petcock with a brand new one. This one is functioning properly. By that I mean it flows in the prime position and doesn't flow in the on or reserve position unless their is a vacuum. The leaking from the carbs doesn't occur when checking float levels off the bike, but as soon as I put the carbs back on and start the bike up it will start leaking gas from somewhere between carbs 1 and 2, at least I think this is where th leak originates. The gas will then continue to leak albeit slowly when the bike is not running and leaks more when running. I've got the carbs off now and I'm gonna go through them again. As far as that diaphragm goes, is there anyway to repair it to find out if that is the culprit prior to ordering a new one? Thank you guys for your help, without it I'd have given up.

 

Tommy I'd suspect one of the o-rings between the carbs.
You know the fuel line tubes man those o-rings cut real easy!
I was able to get some at carquest and then I put some grease on them to reassemble (a light coating)
This is a pain because you have to take the cold start linkage apart to split the carbs, I presume you have already done this before!?
Just in case you haven't, you will be better off to take a few pics with the old digital camera just for memory sake.

good luck
just my best guess
Mike

 

Hey Mike thanks for the input. To be totally honest with you, I didn't know there were o rings between the carbs. I've definately never seperated the carbs before. I'm a nurse not a mechanic. Though right now I wish I was a mechanic. As far as the orings you speak of go, could they also cause my idling problem? Or am I looking at two seperate problems, first being the leaking gas, and second the idling problem? I keep hoping that it's all one problem, but I'm starting to believe otherwise. Thanks again, Tommy.

 

Orings on the fuel passages are a good culprit. Even with a new petcock if there is crud in the tank then it may enter the petcock and keep the oring on the plunger to the petcock diaphraghm from seating. If it is the fuel passage oring then fuel will drop from the outside of the carb and there will be none in the airbox. If there is fuel present in the airbox then it can only get in there by getting past the float valves.
When you take the carbs off check the float seats very carefully for scoring or a deep scratch. If you find one then polish the seat with the tip of a wooden golf tee. Also check the float valves and make sure the mech used new ones. Then check the floats movement on their pins. These can rust and lock good new parts up. To fix this , remove the pin and it's float and insert the pin in a dremel tool. Spin it slowly using mothers metal polish or rubbing compound or even valve lapping paste. This will polish the pieces together and free them to work properly. Let us know what you find and any thing else we can help with.

 

Tommy remember that splitting those carbs is somewhat complicated and there are vent T's as well as a Fuel line T, there are also straight pipe connectors that link the fuel passages so the float bowls will fill and they need to go back exactly the same as they came apart.

PLEASE use the camera carefully BEFORE you start dissasembly.
You will need to look at those pics for sure.
Also did your mech replace those float valves?
Check the rubber seats on the needle valves if they are messed up by all means replace them. It could save you a lot of R&R of those carbs.

When you get the float bowl off and any other parts where jets are exposed make a schematic of where they came out and what size they were in the spot they came from.

There is also a link on this site that refers to polishing your slide valves that is highly recomended.

As for the idle, I really dont understand. Was it missing between 3-4K ?
When you break the carbs apart you'll need to sync those carbs when they go back on the bike.
Also drill out the cap on the fuel air mixture screw while those carbs are apart (much easier) but becareful not to drill thru and hit the screw or it can be damaged.

Good Luck'

Mike

 

I'll definately take heed to the picture advice!!! Before I tear the carbs apart I was wondering if I could test to see if the orings between them are the culprit. Here's how I thought it might be possible. With the float bowls off of all the carbs except #1 gently push up on the floats to seat the needle's of carbs 2,3 and 4 then find a way to keep the floats in place(maybe tape or something) then pour gas in the fuel line and wait to see if it leaks, and from where. I'm just really hesitant to pull the carbs apart if I don't have to. As far as the idle goes, when I start up the bike I have to use the choke, Once I get going and turn the choke down I have to use the throttle to keep from stalling, but If I give it too much throttle or rev above 3000 it will hang there for a bit then slowly come back down.

 

One method that I used to check the seats for leakage is to have the rack of carbs upsidedown with the float bowls off, a length of tubing connected to the fuel inlet line, a small amount of fluid in the seat, blow gentle on the tubing and see if there's any air comming past the valve seat. Gentle movement of the float up or down will aid in seeing how the float valve shuts off the fuel flow.

Not scientific, but can give an idea of problems.

 

find anything? Tommyhawk

 

Tommy, sounds like the main jets are clogged by the choke starting method you described.
under the main fuel jet is a tube with a bunch of holes sometimes these get plugged.
when working properly, the slide valve should open raising the needle valve alowing fuel to be sucked into the air stream going into the intake, but it sounds like those holes might be plugged or restricted.
sounds like you are using an alternate path to get the fuel to the air.
(layman terms)

Also when your carbs are off you should be able to lift on the slide valves and they should all take the same amount of time for the spring to seat them. If one closes faster, that diaphram has a problem, I bet it's the one with the cold cylinder.

Mike

 

Tommy, here is the fellow who makes the stainless steel carb bowl drain screws:
Here's a link to a guy who makes new ones with hex heads.
Steve C (stevec5000@yahoo.com or stevec5000 @ gmail.com) is your guy for
float-bowl drain screws. I think they were $10.00
His work is here: www.mesanet.netfirms.c...Screws.htm

I source all of my other stainless hardware at the local Ace hardware or other similarly stocked place. Just be sure to take along a sample of what you want for pitch and lenght comparisons. Best of luck to you!

 

SUCCESS!!!!! Thanks to all who helped!!! After reading all of your comments, I took a couple of days to let it all sink in and then headed for the garage. Nick, your idea to check the seats ws awesome. That was the first thing I did, and I found my problem. When I had the carbs upside down I attached some tubing to the inlet like you said and blew into it. To my surprise I heard whistling. My first thought was that air was sneaking past the float valve. It turns out that that Mike was right! The leak was coming from the orings between the carbs, man were they shot, when I first saw and felt them I thought they were plastic or soft metal. Pulling the carbs apart was actually not that difficult(turns out I had removed the cold start linkage, I just didn't know that's what it was called). I replaced all the orings, there were 8 in all, with 6mm inside diameter 8mm outside diameter orings from local auto store. Once I got it all put back together I started the beast up, and to my amazement, there was no longer leaking gas!!!! The other problem, the vacuum leak also seems to have disappeared. Now I think the carbs really need a good synch and colortune. If I only knew how...Oh yeah thats right I can find out here via search. Currently the bike is running better than it ever has(since I had it anyway). I just can't get it to idle, tried the idle adjustment screw, but while adjusting it the bike either dies, or idles at 4k. I assume this is because the carbs need adjusting. Am I right? Well Thanks for the help guys. You all just save my last part of summer for some good ride time!!! Tommy

 

Good stuff Tommy.

Yep, It sounds like you need a carb sync now especially if you have had them apart.

You could have bench synced them to give you a good starting point to go from.

Do a search on bench sync and manometer and YICS. There is plenty of good info on this for you to study up on.


Cheers
HG

 

Good work Tommy!!
Yep, you need to sync those carbs and set the mixture screws now.
You will probably find that yu wil need to sync and adjust the mixture screws several times, each time you change one setting it sems to have an influence on the other. (if your out fairly far)

If you can get your hands on a 4 cylinder manometer, you can do the sync yourself but if not I recomend taking it to a shop.

If you go to a "rip-off shop" you'll know because they will give you a bunch of crap about how they can't sync these carbs because YOU had them apart.
They are making excuses before they even start!!

Check out this link to Daves XJ page on carb repair:
http://members.tripod.com/dave_jack/id38.htm

Good luck
Mike

 

Glad my suggestion helped Tommyhawk!

If those o-rings were shot, I'm concerned that the seals on the butterfly or throttle shafts may be shot also. They can contribute to the 4k idle, at least they did on mine. I have some pictures of my worn out seals in my gallery.

A quick inspection of the outer two carbs can be done by removing the e-clip and washer to expose the seals in question.