Welcome back !

Any leak of this type speaks to the inability of the carb's float system to seal. It could be one of several issues, but if you're going to open up the carb, owing to the age of the bike, you might want to simply do them all to BOTH carbs.

(If you are unfamiliar with the carb float system, it works exactly like your home flush toilet. A float rides on the surface of the liquid which controls a valve. When the liquid is at the correct height the valves stops new liquid from entering. When the liquid level goes low, replacement liquid is allowed to enter.)

• The most common of all float issues is simply trash stuck between the float needle and the seat. This holds the float valve open, thus allowing fuel to enter when it shouldn't. Typically, this is a tiny spec of rust from an older tank. The particle is so small you'll need to spray out the carb body over a white paper kitchen towel to find it. The offending fleck will literally be about the size of a period at the end of this sentence. It could also be a small piece of fuel hose. Aging fuel lines get hard, and tiny pieces can break off and cause this type issue.

• Unlike the all-metal R75 float needles, the R100's have a float needle that is tipped in some sort of elastomer (neoprene and viton are commonly used). For the sake of clarity, we'll simply call it "rubber". After long service this "rubber" will harden and take a set. 1) Hardening defeats the design intent and makes it more difficult to seal. 2) The dimple caused by sitting in the same position for decades also raises the float level and can promote leaking.

• During long storage, if fuel is left in the float bowls the floats themselves become coated with a thick varnish. This coating changes the weight of the float, thus making the float ride in the pool of liquid at a different height. For this reason older float bodies simply need to be replaced.

♥ Without going into my fully orchestrated rant on ethanol fuels (found elsewhere on this forum), I do have to point out that ethanol has a hand in tank rust, hardening of fuel lines, and the varnish coating left inside the carbs. So if you see these issues inside your carb, then you really should consider changing your motorcycle storage procedures.

In your shoes, I would first attempt this repair myself. Work on 1 carb at a time to avoid mixing parts. I'll break it down into 2 steps....

► Level 1 Easy initial work. The carbs can stay on the bike.
Obtain modern ethanol-proof fuel lines, new float bowl gaskets, new floats, new float needles, new float seat o-rings, and a can of spray carb cleaner. Remove all the old fuel lines. Remove the float bowls, old gasket, old float, and old float needle. Before the new fuel hose is fitted, spray carb cleaner down through the brass fuel entry tube. This will wash any trash out of the float seat. Install all the new parts. Motor oil applied inside the new fuel lines will prevent a struggle and insure that pieces of the new fuel hose don't break off and enter the fuel system.

If you find a thick brown or green varnish inside the float bowls or on the float, then you may have added issues which you'll want to address while you have the carbs open.

► Level 2 The whole enchilada. The carbs come off the bike.
Brown or green ethanol varnish speaks to long term storage (longer than 3 months) with ethanol fuel present in the system. This promotes rust in the fuel tank, faster aging of the "rubber" parts, and a lean running condition that will eventually damage your engine. You don't have to go to BMW school to know these aren't good for your motorcycle. Replace all these additional parts: slide needles, needle jets, pilot jets, CV diaphragms, head-to-carb hoses, and all the o-rings inside the float bowl. Because the carb cables had to be disconnected for this step, the carbs will need re-balancing after a 5 mile warm up ride.

Click Here for the DIY Carb Balancer

Hope this helps.

There is not much to add to Wobbly's excellent response. That hole in the body under the Bing placard is there in order to equalize the air space above the fuel level in the float to atmospheric pressure. The idea being to ensure that the float chamber is the same as outside conditions regardless of elevation or weather conditions. This "vent" is placed high enough on the carb body that if fuel is gushing out there, fuel might also be dribbling into the motor which could compromise the motor oil.

my new RS

Thanks, I got the float to seat properly and got it started for the first time in three years. Sounds great!

Congratulations ! That's really good news.

Now here's the bad news. 👿 Do you know what held the float open ? Did you hold a paper towel under the carb and catch the offending culprit ? The stuck float is only a symptom. If the root cause is tank rust or rotting fuel lines, then it will happen again. So while you may have repaired the symptom, the root cause could show its ugly head again next week.

This is why I suggested the long list of parts in the previous post. And you didn't tell us if you saw any varnish. So while I'm happy you're happy, I can't offer any assurance you've seen the end of this.

All the best.

cleaned inside of fuel tank and screens, new fuel lines, used compressed air on carb fuel intake passages, no varnish, float worked properly at that point. thanks for the help.

That sounds very promising. Congrats.