What is leaking from my carb, should I be concerned?

[gggGary]

I think this is a misconception. The carbs will only overflow if the floats are not set properly or if the float needle is worn out. A leaky pet cock will cause a strong odor of gasoline in an enclosed space, such as a garage, because the leak replenishes the aromatics (as in aroma) as they evaporate as the aromatics are the first component of gasoline to evaporate. If everything is tight, then once the aromatics evaporate, there is no more so the evaporation of the rest of the components is slower and not as aromatic.

I also turn on the petcock (to prime position) if the bike has been sitting for awhile in order to replenish the aromatics because without the aromatic component, the gasoline in the bowl is really not gasoline. I also move the bike back and forth and side to side in order to mix the aromatics in with whatever is in the bowls. Starts are much better this way.

OK make that a float issue won't overflow the bowl (much) unless the petcock is also leaking.... If there is a leak most of the time it's the low side (LH) carb that leaks.

 

[pamcopete]

gggGary,

That is true. Perhaps my take on the subject is with the bike on the center stand.

 

[estcstm3]

You all obviously have alot more experience than me.

So what are my next steps? Anything I can do (photograph, try) to hep this along? I am still not sure I should be worried.

 

[XSLeo]

On a 75 it has two manual petcocks as it came from the factory.
The vacuum operated came later, 78 I believe.
Anyway on either set up the float valves are not fuel shut offs, if they were Yamaha wouldn't spend all that money putting petcocks on.
The float valves are fuel metering devices. The petcocks shut off the fuel flow. Even with good floats, float valves , and adjustments there are times they will over flow if the petcocks are left on.
My 75 would over flow the carbs if it sat in the sun with about a 1/2 to 3/4 full tank.
The sun warmed the tank, this expanded the air inside, pressurizing the tank. This pressure would push fuel past the float valves if I had the petcocks on. This was because of a Plugged cap vent. But this is just one example.
The vacuum petcocks would prevent this because they shut off the fuel when the engine isn't running.
Now if your petcocks are off no fuel can flow so the carbs can't over flow. With them left on your carbs can over flow.
As mentioned the aromatics evaporate from the fuel, this evaporated fuel leaves out the float bowl vents. This lets the fuel level in the carb drop, Opening the valve. If your bike is setting on the side stand the float can rub and bind, It doesn't take much. But this can lead to fuel overflow if your petcock leaks fuel when off.
There may be other reasons your float valve gets opened, dirt stock on the needle or seat. Varnish on the float pivot, whatever.
So by saying leaky petcocks cause over flow is correct. It your petcock doesn't leak there can't be any fuel flowing to the carbs to leak.
Leo

 

[weekendrider]

I wouldn't be worried. Now 5twins, Pete and
Retiredgentleman it would bother. I'd ride it and shut the petcocks off 100 yards before I stopped.

 

[estcstm3]

Thanks all. I try to always put it on the centerstand and turn the petcocks off, but it has been sitting with them on so that makes sense!

So to be really anal I should look at rebuilding or replacing my left hand side petcock?