Looking for confirmation on likely source of fuel leak

[sacruickshank]

When doing a leak test on my carb bank, I'm getting a fuel leak from carb3 in the red area below. If I read the diagrams correctly, this port bring air to the main jet/emulsifier tube area that is closed off by the main needle. I assume this leak means the valve for that carb is not sealing correctly. Does that sound right? Could it be something else?

The carbs are still in the rack, but I used an old one that was already separated for the pic below.

Thanks

PXL_20250209_165619484-EDIT.jpg

[zed1015]

Yes! It's the main air jet passage to the needle jet tube and likely overflowing due to excess fuel height in the bowl caused by either a sticking/leaking float valve or similar.

[Big T]

O ring failure under the float needle seat

[chuck hahn]

both of the above answers are possible causes First id revisit all the float hts and be sure side in each carb is the same. Remember hts are checked without the gasket in place, work the flots up and down with the gasket in place and watch the floats arent dragging on the gasket causing them to hang up.. it does happen.Run a line from a gravity bottle with water and hold the float up on that carb and watch what leaks or IF anything leaks. If alls good drain the bowls and blow compressed air through the rack to blow residual water out.

[sacruickshank]

O ring failure under the float needle seat

Sounds like a simple solution. Getting them out without damaging the valve holder ... not so simple.

[Nessism]

You might want to bite the bullet and do a full and complete carb rebuild. Never a waste of time on an original set with old and hard O-rings.

The float valve sometimes is hard to remove, and that's because the old O-ring has turned hard and petrified. Some heat on the carb body, around the seat, will help soften the O-ring. Be careful when removing the seat, so you don't damage it.

Check my signature for a copy of a rebuild tutorial that many people find useful.

[sacruickshank]

You might want to bite the bullet and do a full and complete carb rebuild. Never a waste of time on an original set with old and hard O-rings.

The float valve sometimes is hard to remove, and that's because the old O-ring has turned hard and petrified. Some heat on the carb body, around the seat, will help soften the O-ring. Be careful when removing the seat, so you don't damage it.

Check my signature for a copy of a rebuild tutorial that many people find useful.

You're right that I've been doing the quick & dirty carb update so far. The bike was previously only firing on 3 cylinders, then I corrected the valves clearances and would like to try a restart again before doing a full proper carb job. The carbs have some other issues, like frozen mixture screws on three of the four carbs, that will eventually need attention. Haven't yet tried heat on them, but that might be needed.

If memory serves, you helped out with a past GS project, that one was a650L with outer carb bodies corroded so badly two needed replacement.

[Rich82GS750TZ]

What's your hurry? You already admit multiple carbs have problems. You already know it won't run correctly as is. Yes, Ed is the carb man, has helped many. Do him proud and do it right. Just my opinion, of course.

[rphillips]

You probably already know, but breaking a post while removing floats happens a lot. Be careful.

[dgates1]

This was my experience on the stuck fuel mixture screws. Don't do what I did and break off a screw extractor in there!

https://www.thegsresources.com/_forum/forum/technical-forums/carb-fuel-exhaust/1747809-fuel-mixture-screw-stuck

[Nessism]

You probably already know, but breaking a post while removing floats happens a lot. Be careful.

The post won't break if the person follows the instructions provided in the rebuild tutorial linked in my signature.

[sacruickshank]

The post won't break if the person follows the instructions provided in the rebuild tutorial linked in my signature.

I've taken apart dozens of carbs and haven't broken a post yet, so I'm not worried about that.

At this point, I'll start a full tear down since putting each carb in my ultrasonic cleaner may unstick both the leaky valve seats and the stuck mixture screws.

The engine is not yet ready for a test start anyway since the gasket surfaces are not yet clean.