1984 Suzuki FA50 - Carburetor Vent Port -and- Leaking Gas

In reviewing the stock carburetor on my 1984 Suzuki FA50, I have a general question regarding the port as shown with the red arrow in the sample pics attached (not my actual scooter). This port appears to be just a vent port as the stock carburetor had a black hose connected here which went directly up in to the area under the seat and was connected to nothing else. What is the purpose of this port and does this even need a hose connected to it?

In addition, I also have been fighting with gas leakage through the small hose on the bottom of the carb which appears to serve the dual purpose of draining the bowl for storage when loosening the drain screw -and/or- automatically draining the bowl through the overflow pipe located inside the carb if the bowl gets too full - correct? It leaks small amounts while driving and after stopping while the petcock is either in the ON or REServe setting and with the drain screw closed. Is this only possible if the needle valve is not fully seated or the floats need adjusting? Anybody else have this issue and how can I get it to stop?


Suzuki FA50 Carb Pic for 2nd markup Question.jpg
Suzuki FA50 Carb Pic - Marked Up.jpg

Re: 1984 Suzuki FA50 - Carburetor Vent Port -and- Leaking Gas

Steven Bolduc /

Put hose on for atmospheric pressure

Re: 1984 Suzuki FA50 - Carburetor Vent Port -and- Leaking Gas

Adjust the float height and that should stop the leaking.

Does the FA a vacuum/diaphragm petcock? Also is it oil injection?

Re: 1984 Suzuki FA50 - Carburetor Vent Port -and- Leaking Gas

The petcock is vacuum operated as you can see in the overall pic. The oil is separately injected into the reed area directly after the carb which can also be seen in the pic.

Re: 1984 Suzuki FA50 - Carburetor Vent Port -and- Leaking Gas

Then it’s just an overflow if the bike tips over

Re: 1984 Suzuki FA50 - Carburetor Vent Port -and- Leaking Gas

If this is an overflow for drainage during "tipping over" as Ugp suggests, I am wondering why the original black hose would have gone "up" into the area under the seat instead of down to the ground for proper drainage to avoid gas getting where it shouldn't and becoming a fire hazard. Also, why the need for (2) overflows then since the tube at the bottom serves this purpose as well?

Re: 1984 Suzuki FA50 - Carburetor Vent Port -and- Leaking Gas

I have an FZ50, so it’s similar but not the same. That fitting is an overflow and mine does the leaking thing too unless the float level is just right. Just hang a hose down past the engine so the excess fuel goes on the ground or how it happened to me, in your shoe! Kind of hard to check the fuel level if the carb is on the bike, so I tested it with the carb off and bowl screws out. Personally, I think the tiny needle in these carbs does a poor job against the pressure coming from the petcock. Had a similar issue with some Mikunis on a BMW—brand new carbs

Re: 1984 Suzuki FA50 - Carburetor Vent Port -and- Leaking Gas

The port is a vent to maintain equal pressure ( atmospheric pressure ) inside the carb .

It should have a hose attached and directed downward past the transmission casing , in front of the rear wheel , but , to the side .

If you have strange happenings after a while , check the end of that hose and other hoses . Mud daubers love to use them as 'nests' for their embryos .

You can check the bowl fuel level by attaching a see through hose to the drain nipple and holding the hose up along side the bowl while the drain screw is fully open . The fuel level will equalize and show the exact level of fuel inside the bowl .

When you have the bowl off , polish the float valve seat with q tips and Brasso or the like until it is bright shiny clean . Check that the float needle tip is smooth conical with no deformities .

Re: 1984 Suzuki FA50 - Carburetor Vent Port -and- Leaking Gas

I also had this issue on my 84 FA50. That vacuum petcock is problematic. If the diaphragm starts to crap out, it won't allow fuel to flow and causes starting problems. Also, the fuel leak thing.

My solution was to plug the vacuum hose and fit a generic on/off/res petcock. Start and leak issues solved. All you have to do is remember to shut it off (like most every other bike of that era).

Off topic:

What's your best tips for performance mods. I know. It's an FA50 and it won't go fast. All I want is a strong 30+. Some say it's easy.

Already did reeds, a pipe, K&N air cleaner, and upjet. Runs great and sounds good, but gained very little, still at about 27mph max. Gonna try heavier primary clutch springs and head decking for improved take off. Any other magic from you guru's for better top end?

Re: 1984 Suzuki FA50 - Carburetor Vent Port -and- Leaking Gas

The FA OEM automatic fuel valve is a very nice convenience .

When kept clean with good rubber bits , it functions perfectly .

I had to replace the 20 cent o ring on the plunger , once .

My FA50 does 30+ . It's completely stock , but for a seat foam open cell air filter and the piston crown has been relieved at the ports by about half the distance from crown edge to top edge of the top ring landing .

I run regular gasoline ; 15w40 diesel oil in the transmission and Lucas through the OEM injector .

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