Problems with carbs

[trains]

Hi,
I am new to this site but so far find it really great. I recently bought a 1980 XS1100SG, it was leaking gas past the seats in the carbs, ( it has the o-ring type seats). Anyway this was letting the bike flood and making it run like, well you know. So I replaced the o-rings on the seats and set the float level to what was listed in Clymers repair manual, and when the bike is cold it starts and runs great, until it gets warmed up good. The when you shut it off it does not want to start again, the spark plugs are dry but the air box is full of gas, if you remove the bottom of the airbox it will let gas get to the plugs and start right up again. I removed the fuel diaphragm and am using regular petcoks. If I turn the gas off a little before I shut the engine off, it will not flood the airbox but it still will not start, plugs are still dry. When I redid carbs I checked to make sure they were not leaking before I put them back on, Like I said the bike runs great when it is running, it does not flood backfire or anything else, it pulls really strong, is smooth, ( I have also synched the carbs ) and a joy to ride. If I let the bike cool off after riding, before trying to start it back up, lets say like 30 minutes or so this does not happen. It acts like it is vapor locking or something but I don't see how this can be. Also when I wash the bike it will not run on all four cylinders until I let it set for about 2 hours, I know something is getting wet but I can't find out what? I have been raised around bikes all my life my Dad has collected bikes for years, so I have grown up working on everything from whizzer bikes to Triumphs to you name it, but have never experienced a carb problem like this one. I read Blaine's Xs11 carb FAQS on this site and it was helpful, but I am at a loss to understand how or why this is happening, if it will flood the airbox how can it not flood the cylinders? Also this does not happen all the time, some days it runs and starts perfect all day? Any help at all on this would be GREATLY APPRECIATED. you can e-mail me directly at trains@itlnet.net if you have any advice at all on this problem. Thanks from Monte

[TheDjost]

Try running the bike without the airbox for a while and then let it sit. You will see wich carb is leaking.

-Justin

[TopCatGr58]

Hey there Trains,

This seems to be the topic de jour this weekend!! The gastank has a small vent inside the cap, a pinhole sized hole. You can take the cap mechanism apart and inspect that little washer type disc and make sure it has that hole open.

You say you've replaced the Octy system with direct petcocks to carbs. You could still be getting particles of crud from the tank into the carbs getting wedged in between the needle valves and seats, causing an intermittent leak! Do you have inline filters from the tank to the carbs? Did you thoroughly inspect the tank when you replaced the petcocks, find a bunch of rust and crud inside. If you just rinsed the tank, then you are probably still getting crud, you may need to recoat/reseal the tank!?

Does the leak occur when the bike is parked on sidestand vs. center stand? Could be slightly sticky float hinge pin not allowing it to swing thru full travel range to seal? You checked the carbs for leaks, did you check the floats for leaks?

Not starting when wet, could be spark wires/plug caps, could be rubbed wire exposed and shorting to frame thru water?
Not starting when warm, you say plugs are dry, sounds like you're just a bit lean, did you try pulling the choke out to the first notch when warm? Are the plugs pristine bleachy white? If so, then you may be running too lean, and as the bike warms up it gets leaner! You may need to adjust the idle circuit, float levels, and even main jets if you've modified exhaust and intake!

The OEM petcocks have a prime function to provide fuel directly to the carbs bypassing the OCTY for starting, but with replaced petcocks and no Octy, that shouldn't be a factor since you should be getting flow to the carbs as soon as you turn on the petcocks!? Once mine is warmed up I don't ever have to touch the choke, but I have richened up my pilot/idle circuit screws and gone with larger jets due to my modifications!

Finally, welcome, this is a public forum so that ALL members can discuss and learn from each other. Some folks do send private messages/email replies but usually about personal matters or private sales negotiations. We usually post replies to tech problems publicly so that we can see what others have suggested and add other ideas. If every one sent you private emails, then you could receive 20 similar suggestions and we wouldn't know what was told to you. If it's important to you to ask, then you'll need to check back for your answers. Not trying to be mean, just factual about how this system works. Lots of info available here just for the asking, good luck!!!

[rover]

When you replaced the o-rings on the float valves, you might have distorted one of the brass tubes that the float valve goes into. Next time you have the carbs off, pull all the floats and valves out, find a drill bit that fits fairly snug in the valve tubes, and check all four to see if you distorted any of them. I did on one of mine, and spent most of last summer looking for the intermittent leak, until I found one of the tubes just a bit distorted. I carefully reamed the bad one with the drill bit, and had no problem since. Also double check the o-rings. It is very easy to tear one of them. I put a light coat of grease on mine before I put them in. Also, check the pick-up coil wiring harness for a break in the outer housing of it. The harness comes out of the timing housing, runs along the bottom of the trans cover, and around the back of the engine to a plug benind the fuse box. Any water on the road will get in any breaks in this harness, and could cause wet running probs.

[trains]

Hi,
Thanks for the suggestions guy's I will check into the possible fixes you all suggested. The tank is perfectly clean and yes I am running filters so that is probably not the problem, yes the bike is running a bit lean, but other than adjusting the screws ( I have them set at about 1 1/4 turns out now ) how else do you adjust idle mixture other than changing jets, which by the way are all stock and I have made no modifications to the bike. All jets are stock, and I have set the floats to what Clymer's says they are supposed to be, and they are not leaking, I have not checked to see if one is sticking though. I still do not understand how even when the carbs do leak, ( which like I said this does not happen all the time), how does it fill up the airbox without letting gas get to the plugs? It seems to me that the vapors alone from a full airbox would let the thing start, but instead the plugs stay perfectly dry!! But I can take off the bottom of the airbox and it will let gas get to plugs and then it will start. I am going to buy all new needle and seats and start over from there, I will let you know how it works out. Once again thanks for your help.
P.S. It ran and started fine this weekend so I was able to get in some good riding.
Thanks again Monte