help with new tank

[quikvrsixx]

just finished a ground up build on a 1981 gs750L. installed a new tank and petcock. the new petcock has only 1 outgoing line which i hooked up to the fuel intake on the carbs. bike runs but my problem is if i leave the petcock in the open position overnight the fuel drains out of the tank. seems like it is coming right out of the air filters i put on (individual cones). my other question is the line coming out of the carbs right in the middle of the slider for the choke seems to be a vacuum and i have nothing to hook up to it now. if i cover it up the bike runs, if i leave it open is seems to stall out? what was it for and how to resolve the problem.

[Macguyver]

Sounds like you have a manually activated petcock. No vacuum line to the carbs required. The only thing that is required is that you turn it off every time when done riding the bike.

I would also check to make sure there is no gasoline overflowed into the engine oil, this can be very bad.
If the oil smells like gas, drain all of the oil, let the bike sit for an hour or so to let any gasoline residue evaporate, and refill with fresh oil.

The open line coming from your carbs is the vacuum line for the O.E.M. vacuum operated petcock. This line MUST be capped in order for the bike to run properly with the petcock you have, otherwise you will have a tragically unbalanced lean condition with the carbs. Go to your local auto parts store and buy a rubber vacuum cap in the appropriate size, it'll be a buck or two at most. Remove the vacuum line from the carbs and cap the barb on the carbs.

-or-

Plug the rubber line with a tight fitting bolt.(not recommended)

The only line left should be your fuel line going to the carbs.

Enjoy the bike as usual, and make sure to remember to turn off the petcock when you get to where you are going.

Best of luck, and post some pics for us when you get the chance!

[Larry D]

^^^^^^^^^^

What he said. Especially the part about fuel in the crankcase...not good.

[BassCliff]

Greetings and Salutations!!

Hi Mr. quikvrsixx,

So I take it you did not install a stock petcock? Don't forget to plug the vacuum line that normally comes from the #2 carb to the vacuum input on a stock petcock. See THIS ARTICLE for more info on the stock petcock arrangement. Yes, you'll have to turn the fuel supply off every time you park the bike. Normally, the lack of engine vacuum to the petcock will do this for you.

Anyway, I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[texaninseattle]

I may be WAY out in left field on this one BUT, if his floats are adjusted properly, shouldnt they stop the fuel level from rising in the bowl to the lever where they leak from the vents?

[BassCliff]

I may be WAY out in left field on this one BUT, if his floats are adjusted properly, shouldnt they stop the fuel level from rising in the bowl to the lever where they leak from the vents?

In a perfect world float valve seats would not leak. But we do not live in a perfect world.


Thank you for your indulgence,

BassCliff

[quikvrsixx]

thanks for the help. i was thinking that the float probably had debris stuck in it and if the seats were good it would only fill so high. the carbs were off the bike for almost a year so i am sure there is some dirt in them. i am planning on having a friend rebuild them soon, but realize i will have to shut the petcock off every ride. thanks again and i will post some pics of the bike up soon.

[SqDancerLynn1]

The design of the metal/metal float assemblies does not make a perfect seal. Under running conditions they work great. When stored they can seep fuel if not shut off

[Calvin Blackmore]

The design of the metal/metal float assemblies does not make a perfect seal. Under running conditions they work great. When stored they can seep fuel if not shut off

they get grooves worn in em too.
I assume leakage starts after the mated parts get out of spec.

I have a few set of carbs and one that i got had very worn valves
my originals have the slighest of marks on them.