Topic: gas leak?

[slowjo]

So I had to go out to my shed to get the registration for my 1972 CB750 K1 so I can get a new sticker the license plate and I got the strong smell of gas coming from inside. From what I can see the gas is leaking from the #1 carb and leaking from the airbox. The bike has been sitting for the last two months since I live in Ohio. The petcock was turned off when I stored the bike. Any ideas in where to start? Should I jump right in and remove the carbs to clean them? Or could it just be something simple? Thanks.

[ekpent]

Sounds like the petcock is not shutting off and gas is leaking by. There were a couple threads on that awhile ago,maybe a fix.

[slowjo]

This bike is relatively new to me. I purchased 3 years ago. Its my first street motorcycle. I did notice that at the beginning of last year that the oil really smelled of gas after sitting for winter. Also when it would set for a day or two it was hard to start, but if it was ridden earlyer that day it would start right up.

[ekpent]

Here is one thread to get you going.  Eric    http://forums.sohc4.net/index.php?topic=77408.0

[slowjo]

After reading that thread I'm still confused on what to do. Try to fix it or purchase a new one? Decisions decisions.

[flybox1]

even if the PC allowing gas to leak thru, the floats are not doing their job in closing the float valves.
and they should....

if its been sitting, there may be varnish buildup.
clean your tank of old gas and fill with new. add fuel stabilizer of your choice.
check PC, make sure it shuts off fuel while its NOT connected to carbs.
pull carbs.
clean
clean again, and check how your float valves seat.
are the orings good? do they seal? is the valve spring...springy?
reset float heights, check 2-3 times for accuracy.
reinstall and SLOWLY turn on fuel while banging on carbs with a wood block or rubber mallet.
this will free up the floats and let them shut off float valves.
if you still get a leak, its time to get into the whys your float valves not shutting off.
bad fit, sediment or varnish in the way...etc.

get on it and report back  

[slowjo]

The bike barely ran when I first got it. So I'm sure that the carbs could use a good cleaning, at least I would know whats going on in there. The bike would leak gas out #1 fuel bowl when it sat for long periods of time while on the kickstand. Right now its sitting in the center stand and it looks like gas is still leaking from it.

[flybox1]

just cleaning the carbs wont be enough if your tank is dirty and continues to contaminate your fuel system.
a clean tank =  clean fuel and less crap in your carbs/engine.

[slowjo]

The tank looks clean. No rust inside. When I replaced the fuel lines two years ago I flushed it out. Last year I stored the tank inside and used marvels mystery oil. This year I left it on the bike and filled it up with gas. I also used sea foam.

[flybox1]

nice...id move right into tearing those carbs apart and getting everything super clean and dialed in.
probably the combo of float heights and varnish causing the continued leak.

[slowjo]

I do have one of those kits inside my motorcycle tool box. I have learned over the years by working on cars that its best to have the replacement part before you take the old one off. I also have a spare petcock.

[Silverback]

Same issue here! I fixed it by replacing the petcock AND replacing the float valve. I tried to lap the float valve needle into the seat for a better seal (Has worked many times), but it was too far gone.

[slowjo]

I took a closer look at the petcock and it looks like one of the fuel lines came loose. One line is the correct 5.5mm tygon line, and the other line is 3/16th line. I replaced both lines with the 5.5mm two years ago but one of them had a real bad kink so I replaced it with 3/16th line from the parts store. Now the 5.5mm line is hard as a rock and its the one came loose.