carb fuel level window???

[LOOMER]

Just recently i noticed the fuel in the window will disappear after about an hour. I don't see any noticeable leaks anywhere. What could this be air leak, bad fuel pump or??? I did notice when the choke is pulled it will bubble. I don't know if this is normal or an air leak somewhere. Carb is a stock asain. I don't think the fuel is boiling. It does have the heat riser.

thanks,

 

[Pighead]

Wow. You have a lot of patience to watch your porthole for an hour. I could assume a dropping fuel level could be due to a weak fuel pump, or a clogged fuel filter...
I have never noticed bubbling...where do you see bubbles?

 

[k91]

This is interesting, mine does the same thing and I am having issues with the way it runs...Mine will studder and backfire when I try to accelerate, does yours?? I also noticed the smell of gasoline in my oil...I am aware that fuel smell in your oil is typically a leaking fuel pump, you may want to check your oil, Matt

 

[fj404life]

I dunno if this can happen on a 40 but it did on my Suzuki 4 stroke dirtbike.
Carb float seal was leaking and the petcock (valve on tank) decided to start leaking too.
Went to start bike (e start) motor seized up. Cylinder full of gas, oil full of gas.
This is a gravity fed system though.

 

[FJ40Jim]

If there is bubbling in the window, the fuel is boiling. Gasoline is a hetereogeneous mixture w/ the components having different boiling points, from STP up to hundreds of deg. F. The lighter components are cooking off, lowering the fuel level below the sight glass.

This is not a problem, unless it boils the carb dry, making it difficult to restart. In that case, something will have to be done to reduce the boiling. Possible fixes include: unstick the heat riser flapper, cold ram air to aircleaner, lower temp T-stat, higher BP fuel, add a carb cooling fan...

 

[LOOMER]

It seems to run fine. I do notice a little studder when accelerating but nothing major. However, when running the fuel level is correct. The bubbling fuel is when the engine is cold and choke out. I can see it in the site glass. When i push the choke in the bubbling stops. How would a faulty fuel pump or clogged filter affect the fuel level as far as going away. I could see those being an issue if the fuel level never got up the correct level. But mine does it just leaks back down somehow somewhere.

 

[k91]

Did you check your engine oil to see if smells like fuel??

 

[LOOMER]

yep, no fuel in oil.

 

[Pighead]

However, when running the fuel level is correct. The bubbling fuel is when the engine is cold and choke out. I can see it in the site glass. When i push the choke in the bubbling stops. But mine does it just leaks back down somehow somewhere.

Hmmmm....interesting. Just a WAG, but maybe when the choke is pulled, perhaps vacuum levels change at different levels in the barrel? Maybe there's a missing or stuck check ball somewhere allowing air in backwards? If the fuel level is halfway up the porthole and the needle valve is closed and no gas is coming in air is somehow getting sucked into the bowl? Are your two bowl drain plugs tight with gaskets? (could also explain the fuel draining out).
I haven't had my carb apart in years since the Professional Rebuild (Thanks Jim C.) so I'm a little rusty on the inner workings...Not that I was ever an expert.