Disappearing Fuel

[IOMC Hardtail]

Bike: 78 xs650SE, BS38 Carbs

History: Bike is in mid build (running and riding). I have one of those fancy dancy glass fuel filters with the replaceable filter element inside. I recently rebuilt the carbs with the kits from MikesXS and cleaned them thoroughly during the rebuild. Bike runs great.

Issue: When I park the bike, turn off the fuel pet cock, the glass filter is full of fuel. Over a period of about 3-4 days, all the fuel in the glass filter disappears. The three possibilities I've come to are (I'm sure there's more):

1. The fuel is somehow evaporating from the bowls and allowing the fuel in the filter do drain down the lines and into the bowls

2. The BRAND NEW float valves aren't seating properly and are allowing the fuel to fill the bowl (I'll touch on this here in a second)

3. There is a small leak somewhere in the fuel lines and it's slowly dripping out (my garage smells like fuel)

About #2: Before I rebuilt the carbs (when the bike was running like crap), one day I took it out for a ride, filled it with gas on the way home, forgot to turn off the pet cock when I got home. Came out the next day and half of the gas in the peanut tank was gone. Guess where I found it? Mixed in with the oil in the crank case. The level was at least twice as high on the dipstick.

So, what say you 650 Masters??? Thanks.

 

[Paulrxs650]

Hi, it sounds like somehting not shutting off the fuel as it should. Pop the carbs off and check:

1. The floats are not porous - Try and sink them in a bowl of fuel for an hour - watch for bubbles and give them a shake
2. Your floats are in the correct way round and adjusted correctly
3. Your tank and carbs are scrupulously clean
4. Check the petcock by disconnecting the carbs and see if fuel free flows
5. Ive never used the kits from mikes but check the quality of the valve seat

Also drop your oil and replace - fuel will thin the oil and is an obvious dange in itself.

 

[gggGary]

Some gas will evaporate through float bowls but if you can smell it in the garage, yup there's an issue. Have you done the float hot water dip test? Quick dip in steaming hot water, bubbles = fail.

 

[IOMC Hardtail]

I've done the test with the floats, they're good. Just went out there and fired it up. Last time it ran was Friday. The filter was empty. Didn't turn the fuel valve on. It ran for about 30 seconds and then died. Wouldn't fire back up till I opened the fuel valve. So, it seems like the fuel is evaporating. Thinking the plan now is to let it sit for 4 days, wait till the filter is empty again and drain the bowls and see how much fuel is in there.

 

[TwoManyXS1Bs]

Yep, fuel evaporating from carburetors, especially right after parking a hot machine, is normal. EPA mandated evaporative control systems for cars in the '70s to handle this.

My BS38 bowls hold about 40cc of fuel. Drain after a few days, down to 20cc-30cc. After a month, almost dry. Faster evaporation than I remember with gasoline.

Dang gasohol.

A little story:

http://www.xs650.com/forum/showthread.php?p=398967#post398967