Leaky carb

[frosty5011]

I am currently in the process of rebuilding a '78 GS750 that I recently acquired. Originally, the bike would only run on 3 cylinders, and fuel was dripping from everywhere. I rebuilt the carbs, did my petcock modification, put in new induction tube o-rings, changed the oil, freed up the locked rear brake by rebuilding caliper, sandblasted and repainted the rusted up airbox, and a few other minor things ....... and yesterday, decided to fire her up after putting it all together again.

Purrs like a kitten. Drove her around the block a few times, and not a hiccup. Being that I only rode around in the neighborhood, I could only take it up to about 5k rpm's max.....and the bike runs beautifully.

I had only one problem. The #1 carb kept on leaking fuel (about 1 drop every 8-10 seconds) out of the nipple from the overflow tube on the carb bowl. Racked my brains trying to figure out what might cause that. I knew it wasn't the float valves......I bench-tested those and each one closes airtight. I know my petcock isn't leaking a drop. This leaking continued, even though immediately after riding, I put the bike back up on the centerstand as opposed to the kickstand.

I took the float bowl off twice, made sure there was no binding whatsoever of the float against either my selfmade bowl gaskets, or the bowl itself. None. Operated the float by hand with petcock set on prime....No problem, closed off fuel flow completely when pushing up on float.

Finally, I decided to check just the bowl itself. Put the bowl in my little workbench vise......filled it with gasoline.....Lit up another cigarette ..... attached a small hose to the bottom nipple, closed off the top of the brass overflow tube with my finger and blew on the hose. Guess what! Gurgle...gurgle....gurgle....a bunch of airbubbles start coming from the base of the brass overflow tube, where it meets the bowl. No visible damage there whatsover.....no corrosion, nothing. Guess I just have a faulty carb bowl. Tried carefully hammering the tube further/tighter into the body, but that only slightly decreased the leak.

So, in conclusion........anyone out there happen to have an extra float bowl for pre '80 VM carbs? Or does anyone know of any kind of liquid gasket that can be used that will not be affected, i.e. dissolve because of sitting in gasoline that I could smear around the base of the overflow tube?

Any help would be appreciated.

P.S. Many a thanks to Earl, with whom I've been in contact with on this project I've been throwing ideas at him, and picking his brains so much......it's a wonder he can still think straight

[frosty5011]

Here's the bike so far.........1978 GS750. Paid $350 for it in non-running condition. Put $45 into it so far, along with some items which I already had laying around as spares in my garage. Spent about 40-50 hrs on it so far (most of that polishing). Runs like a dream now. Has 12500 miles on it. Still has a ways to go as far as cosmetics.

Mechanically right now: needs new rear tire, drips 1 drop of fuel out of carb bowl #1 every 20 seconds (until carb bowl is empty), and probably needs the grease/oil distribution mechanism replaced....it is kind of rusty.

[Jethro]

Are you sure you don't just need a new float jet? Should be the only thing that can cause the carbs to overflow.

[frosty5011]

Are you sure you don't just need a new float jet? Should be the only thing that can cause the carbs to overflow.

Yep, I'm sure about that, Jethro. The carb is not really overflowing, the overflow tube, where it is pressfit inside the float bowl is not airtight. That's where the gas is leaking through. It gives the impression that the carb bowl is overflowing, but it's not.

[Jethro]

Ahh, gotcha. Sorry, I don't have a carb body for ya.

[frosty5011]

OK,

Due to the wealth of responses received , I decided to try and see if Permatex gasket sealant will work. Will try to put a little "ring" of this around the bottom of the post where it is pressed into the bowl body.

Well let y'all know how it works.

[MichaelHoward]

Looking Good Snowman!!

Hope you get it fixed 8)

Good Luck!