Carbs Leaking

If it was problem with the petcock, why would I only be having problems on 2 carbs ?

Lean angle because you don't have a center stand - I have the same issue thanks to a previous owner. But if you shut off the petcock and the leak goes away it likely isn't the petcock.

mine only leaked out of the two downhill carbs. As long as it was running it was fine but if it sat both of the downhill carbs would be leaking out of the overflows and the pods would be soaked with gas. I think that maybe gravity pulled the gas down to the lowest point which was when it was on the side stand. I could ride it a hundred miles and it would be fine and as soon as you let it sit for a few minutes you could watch gas vent out of the overflow.

The thing you might want to check is -- do you have gasoline in your oil. If your pods filled up with gas then it could have flowed in the other direction too, into the intake manifold. If the intake valves in #1 and #2 were closed, probably not a big deal but still worth checking for gas in the oil in the crankcase.


It sounds like a sidestand issue. I don't have your model bike but I have a Kaw triple from around that same time period and the petcock is *not* vacuum-activated, so I always have to turn the gas to the 'off' position or I get the same symptom as you when the bike sits on its side stand.

The thing that bugs me about this is -- even if I leave my petcock 'On' or 'Reserve,' I thought the float and needle valve, which work FINE on my triple as the bike runs excellent -- why aren't the float and needle valve able to keep gas from flowing into the carb when the engine's not running. After all, with the motor running the float+needle are able to stop gas flowing into the carb just fine.

Bit of a mystery. In your case, if your petcock has On and Res and Off (as opposed to On, Res, and 'Pri' for 'Prime' found on vacuum-operated petcocks) -- you have the same style of petcock as on my Kaw triple.

If you leave the gas 'On' or 'Res' then gas is still in the tank able to flow to the carbs. Turn it to 'Off' and extra gas flow will stop.

The reason you don't worry about turning the petcock to 'Off' on a more modern bike is -- most of them don't have an 'Off', the petcock automatically closes when the engine shuts down owing to a vacuum hose from the carbs to the petcock. This vacuum hose, when the engine turns over, pulls on a rubber diaphragm inside the petcock, and that allows gas to flow to the carbs.

Check for gas in your crankcase, I believe there is some danger related to having gas overflow into your crankcase, not sure of the details, but in any event the gas will affect your oil viscosity.

And if your petcock has 'On' and 'Res' and 'Off' then switch to 'Off' as a habit whenever you park the bike. (You don't have to do that for a newer bike if it has a vacuum-operated petcock.)

check your needles and seats that are controled by the floats. any wear, scratches, grooves, or dirt is bad and can cause problems. in the past on some cb750's I've had I would lower the floats just a bit especially on #1 carb to help. if it was your petcock it would leak all the time. check things while its apart to make sure, but I don't think you really have a problem other than you need to make sure you turn the gas off when its parked. lets say you replace everything in the carbs and have floats set properly etc... If you would then park the bike on the side stand with the fuel valve ON and leave it overnight, you would have gas leaking onto your floor. As would be the case with most bikes that have a "manual" petcock. My bike will do it but I don't have a problem with it because I turn the gas off, however when my brother rides my bike he brings it back with gas stains on my polished covers because he just parks it and walks away! But check everything while its apart, make sure your floats "float".

think about all the weight of the fuel in your tank, 1 gallon of water weighs 8 pounds. so imagine 3 gallons of fuel in your tank pushing its way down the fuel line and into the carbs. the only thing stopping it is 4 little needles that are only being held in their seats by the force of your floats trying to float in gas. it doesn't take much for the weight of the fuel to push past. when the engine is running the fuel is flowing pretty much all the time and needles aren't really fully seated much. the fuel is being used and replaced, flow increases and decreases but is never really stopped. but when you turn the engine off the fuel stops flowing and tries back up and will find a way out.

Gravity always wins and it never stops pushing. You have to polish the needle tips and brass seats so the floats in the carbs are able to stop the gas. The two valves (the petcock and float valves) are in "series" and both working together can keep the gas from flooding.